[Putnam's
Science Series]

The Oldest Woman in the World and her Son

Baba Vasilka is 126 years old, and her son Tudor is 101. They are peasants, and have lived all their lives in a little village in Bulgaria. They are typical examples of people who live to a great age by the use of soured milk, as it has been their principal food all their lives.

The
Bacillus of Long Life

A Manual of the Preparation and Souring of Milk for
Dietary Purposes, Together with an Historical
Account of the Use of Fermented Milks, from
the Earliest Times to the Present Day,
and Their Wonderful Effect in the
Prolonging of Human Existence

By

Loudon M. Douglas, F.R.S.E.

With 62 Illustrations

G. P. Putnam's Sons
New York and London
The Knickerbocker Press
1911

Revised Edition

Copyright, 1911
BY
G. P. PUTNAM'S SONS

The Knickerbocker Press, New York

PREFACE

This book has been designed with a view to meet an extensive demand for definite data on the subject of Soured Milks. The author has had this matter brought before him, times without number, by those inquiring for authentic information on the subject, and he has therefore considered it desirable to gather together such information as is available in connection with ancient and modern practice. He has endeavoured to present this to the reader in concise form.

The author is indebted to many friends for their assistance in getting the book together, and would specially mention Dr. H. B. Hutchinson, Bacteriologist, Rothamsted Experimental Station, for assistance in connection with the bacteriology of fermented milks; Mr. Thomas Douglas, of Wimbledon, who has assisted with the chemistry of the subject; Mr. S. Javrilovitch, of Belgrade, Servia, for local information and illustrations; Dr. Otokar Laxa, Bacteriologist, of Prague, Bohemia, for general assistance; the editor of Bacteriotherapy, New York, U.S.A., for the use of the group of illustrations 30-44; the publishers of the Centralblatt für Bakteriologie, Jena, for the group of illustrations 14-29; and many others, some of whom are referred to in the text.

CONTENTS

ILLUSTRATIONS

THE BACILLUS OF LONG LIFE

CHAPTER I

INTRODUCTORY—HISTORICAL

The milk industry is one of the oldest known to mankind, and it is difficult to imagine a time when milk in one way or another did not form a part of the diet of the human race. There is a good deal of evidence to show that in Paleolithic and Neolithic times, cattle were part of the possessions of the nomadic races; and, according to the Vedas, the manufacture of butter was known in India 1500 years B.C.

In the eastern part of Europe, milk has always been looked upon as one of the principal kinds of food, but not necessarily the milk of cows, as, from ancient times to the present day, the milk from camels, buffaloes, sheep, and goats has been used indiscriminately throughout the East.

According to Layard,[1] "the Bedouins do not make cheese. The milk of their sheep and goats is shaken into butter or turned into curds; it is rarely or never drunk fresh, new milk being thought very unwholesome, as soon by experience I found it to be, in the desert. I have frequently had occasion to describe the process of making butter by shaking the milk in skins. This is also an employment confined to women, and one of a very laborious nature. The curds are formed by boiling the milk, and then putting some curds made on the previous day into it and allowing it to stand. When the sheep no longer give milk, some curds are dried, to be used as a leaven on a future occasion. This preparation, called leben, is thick and acid, but very agreeable and grateful to the taste in a hot climate. The sour milk, or sheneena, a universal beverage amongst the Arabs, is either buttermilk pure and diluted, or curds mixed with water.

The Pass of Bukova.—During the revolution of 1904, a number of Turkish soldiers, just before traversing this pass, were given coffee containing "café" by a Bulgarian coffee-seller, or keeper of a small khan. Whilst in the pass the poison began to take effect, and they realized that they had been poisoned. Fortunately for them, a peasant with three horses loaded with Yoghourt (soured milk) had taken advantage of their escort. The soldiers ate freely of the Yoghourt, which counteracted the effects of the poison.

"The camel's milk is drunk fresh. It is pleasant to the taste, rich, and exceedingly nourishing. It is given in large quantities to the horses. The Shammar and Aneyza Bedouins have no cows or oxen, those animals being looked upon as the peculiar property of tribes who have forgotten their independence, and degraded themselves by the cultivation of land. The sheep are milked at dawn, or even before daybreak, and again in the evening on their return from the pastures. The milk is immediately turned into leben, or boiled to be shaken into butter. Amongst the Bedouins and Jebours it is considered derogatory to the character of a man to milk a cow or sheep, but not to milk the camel. The Sheikhs occasionally obtain dates from the cities. They are eaten dry with bread and leben, or fried in butter, a very favourite dish of the Bedouin...."

The practice is now the same as it was in scriptural times, when milk was looked upon as the principal article of diet, and throughout the Scriptures there are copious references to milk in different forms, some of which are of peculiar interest at the present day.

It may be noticed, for example, that milk is absent from the sacred offerings amongst the Hebrews, and this was ascribed by the late Professor Robertson Smith to the fact that all ferments were excluded from presentation at the altar,[2] it being recognised that, owing to the hot climate, milk of all kinds became rapidly sour, and in this way came to be looked upon as only fit for consumption when in that condition. It has been suggested that the prohibition referred to is on the same level as the prohibition of the use of blood, "as milk has sometimes been regarded as a kind of equivalent for blood, and containing the sacred life."[3] To this day the wandering tribes of Arabia consider the milk of their camels and flocks more refreshing when it has been slightly fermented or soured by being poured into a milk-skin on the inside of which are still sticking sour clots from the previous milking, and there shaken for a brief period; but this slightly soured milk (the Oxygala of Pliny) is known widely in the East simply as leben (milk). The name is also applied to what we term buttermilk.[4]

Kabyles Souring Milk

In the north of Africa the use of soured milk is common, and the illustration shows Kabyles shaking a skin full of milk so as to sour it. The skin has previously been used for the same operation, and, as a consequence, clots of milk are left from the previous day's use, and thus fermentation is set up.

The use of milk-skins for the carrying of milk is not confined to one country, as, while it is common all over the north of Africa, it is also known in the Pyrenees and in some parts of the Balkan Peninsula, the object being identical in each case; and when it is intended to make butter from the milk, the skin is simply rocked between the knees until the butter separates, a process of butter-making which was also used after the introduction of earthenware churns.[5] Dried soured milk is also used by the Arabs, and it is reconstituted when required by rubbing it up with a little water, and it is known as Meeresy.[6] The ordinary soured milk is the common article of diet, and is looked upon as being necessary at every meal, and travellers frequently refer to the use of this product, as a few references will show.

Amongst the peasants at the present day, soured milk is known as _yoghourt_, a word which is spelt differently according to the locality in which it is used. The method of preparation is practically the same everywhere, and a short description of the process as now carried out in one place would, with slight modifications, apply to the general method adopted all over the East.

Charles G. Addison states: "A supper was brought in on a round tray. In the centre was a huge pilaff of rice, and around it several small dishes of stewed meats, grilled bones, sour clotted milk called yaoort,[7] bits of meat roasted, etc....

"We retired into a tent to breakfast, where we found an immense bowl of delicious fresh camels' milk, with thin hot cakes of unleavened bread, baked upon the ashes, ready prepared for us. The principal food of the Bedouins consists of flour and some camels' milk made into a paste, boiled, and eaten swimming in melted grease and butter; boiled wheat and beans dried in the sun and prepared with butter are a favourite dish. They are all remarkably fond of butter and grease; the butter is made in a goat-skin, suspended to the tent pole, and constantly shaken about by the women."[8]

Burckhardt[9] says: "The provisions of my companion consisted only of flour; besides flour, I carried some butter and dried leben (sour milk), which would dissolve in water. It forms not only a refreshing beverage, but is much to be recommended as a preservative of health when travelling in summer. These are our only provisions." With regard to the inhabitants of the Houran, Burckhardt relates that the most common dishes of these people are bourgoul and keshk. "In summer they supply the place of the latter by milk, leben, and fresh butter. Of the bourgoul I have spoken on other occasions; there are two kinds of keshk—keshk-hammer and keshk-leben. The first is prepared by putting leaven into the bourgoul and pouring water over it. It is then left until almost putrid, and afterwards spread out in the sun and dried, after which it is pounded, and, when called for, served up mixed with oil or butter. The keshk-leben is prepared by putting leben into the bourgoul instead of leaven; in other respects the process is the same. Keshk and bread are the common breakfasts. Towards sunset a plate of bourgoul, or some Arab dish, forms the dinner."

Again, Taylor[10] says: "I received a small jug of thick buttermilk, not remarkably clean, but very refreshing."

These references particularly refer to the East, from which it would appear that soured milk was universally known in ancient times as it is at the present day, and this remark applies not only to Egypt, Palestine, and Arabia, but throughout Turkey and the Balkan States, where the consumption of soured milk is equally common. It seems curious that the use of this commodity should have been confined for centuries to the East, as we shall see later on that its dietetic value is so great that it is really a wonderful thing that no one has taken the trouble to introduce its use to the Western nations until quite recently.

The Handling OF Milk in the Pyrenees

The handling of milk in the Pyrenees is, more especially in the villages, conducted in goat or sheep skins, in a similar way to the methods which prevail in Eastern Europe, and the picture shows a skin of milk on a small farm in the Pyrenees. The churning is very often performed by simply rocking the skin between the knees, acidity being induced by remnants of the previous day's milk; souring of milk is induced by the same method.

A curious example of how the virtues of such an article may be independently discovered by another nation is to be found in Lapland, where reindeer's milk is the article used. "The reindeer's milk," says Acerbi,[11] "constitutes a principal part of the Laplander's food, and he has two methods of preparing it, according to the season. In summer he boils the milk with sorrel till it arrives to a consistence; in this manner he preserves it for use during that short season. In winter the following is his method of preparation: The milk, which he collects in autumn till the beginning of November, from the reindeer, is put into casks, or whatever vessels he has, in which it soon turns sour, and, as the cold weather comes on, freezes, and in this state it is kept. The milk collected after this time is mixed with cranberries and put into the paunch of the reindeer, well cleaned from filth; thus the milk soon congeals, and it is cut out in slices, together with the paunch, to effect which a hatchet is used, for no smaller instrument would perform the office of dividing that lump of ice. It is then separated into small pieces and eaten throughout the winter every day at noon, which is the Laplander's dinner-hour. It must be presumed, as it is served up without being brought to the fire, that this is ice-cream in the greatest perfection: here are flesh and fruit blended with the richest butyraceous milk that can be drawn from any animal; but, notwithstanding the extraordinary fatness, which may be supposed to resist in a great degree the effect of cold, this preparation, as our good missionary remarks with a degree of feeling, as if his teeth still chattered whilst he delivered the account, chills and freezes the mouth in a violent manner whenever it is taken. The milk which is drawn late in the winter freezes immediately after being drawn. This is put into small vessels made of birchwood, and is considered by the Laplander as such an extraordinary delicacy, that he reserves it as the most acceptable present he can offer even a missionary. It is placed before the fire and eaten with a spoon as it is thawed. When put by, it is carefully covered up, because if the cold air gets to it afterwards, it turns of a yellow colour and becomes rancid."

Amongst the peasants at the present day, soured milk is known as yoghourt, a word which is spelt differently according to the locality in which it is used. The method of preparation is practically the same everywhere, and a short description of the process as now carried out in one place would, with slight modifications, apply to the general method adopted all over the East.

"The culture," says a correspondent at Varna, "which is used for the preparation of yogourt, is known as 'Maya' or as 'Bulgarian Maya.' The milk which is to be converted into yogourt must first be freed from all bacteria by boiling and allowed to cool to the temperature of 45° C.; it is then inoculated with maya and maintained at an even temperature of 45° C. during several hours. There are two kinds of maya, or ferment, one known as sour, and the other as sweet maya.

"In Europe small stoves, made expressly for the purpose, are used to maintain the milk at the proper temperature. In this country, however, after the milk has been boiled, it is merely poured into a bowl and allowed to cool to approximately 45° C., then a tablespoonful of this tepid milk is well mixed (in a small bowl apart) with a similar quantity of maya, and the mixture, when it has become quite homogeneous, is added to the bowl of tepid milk and stirred slightly. (One tablespoonful of maya is sufficient to ferment one litre of milk.) A cover is then placed on the bowl and the whole is enveloped in flannel and left in a warm place for three hours in summer, and somewhat longer in winter.

"The process of preparation is complete when the mixture assumes the appearance of a soft mass somewhat resembling cream cheese, but less solid. The flannel is then removed, the bowl uncovered and placed in a cool spot until needed for consumption. Of the yogourt thus prepared, a tablespoonful is kept to serve as maya for the following day.

"The best yogourt is prepared from sheep's milk, the second quality from buffaloes' milk, and the third quality from cows' milk. Yogourt forms an almost daily article of diet with the natives in this country."[12]

With regard to the time stated for the fermenting process, it must be noted that since the subject has been investigated so thoroughly, the time required for fermentation has been found to be nearer ten than three hours, but this will be dealt with in a subsequent chapter.

Historically it may be gleaned from the fragmentary references which we have given, that soured milk has, from time immemorial, formed the principal article of diet of a great many peoples, and the notable feature in connection with it is, that in some countries where it is in daily use, the age limit for human beings seems to be very much extended, and it would appear that there is a direct connection between the use of soured milk and longevity. In Bulgaria, for example, it is stated that the majority of the natives live to an age considerably in excess of what is recognised as the term of life amongst Western nations, and inquiry has shown that in the eastern part of Southern Europe, amongst a population of about three millions, there were more than three thousand centenarians found performing duties which would not be assigned to a man of sixty-five years of age elsewhere. It is quite common to find amongst the peasants who live to such a large extent upon soured milk, individuals of 110 and 120 years of age.[13]

In the ancient dairy practice, as we have seen, soured milk was the principal product, and the extraordinary ages which are recorded of the patriarchs, if translated into the modern denomination, would not appear to be so imaginary after all, when it is considered that we have thousands of examples at the present day of men and women enjoying quite as long a term of existence. It has been noticed also, that while these very old people are able to perform a certain amount of manual labour, there is not the same tendency to the mental decay which is so prominent and sad a feature amongst Western nations, at a period of about seventy or eighty years of age. It would seem, indeed, as if the habit of living long was well known in ancient times, and that, like many other of the valuable arts and sciences, it fell under a cloud during the Middle Ages, or, perhaps, the significance of the use of soured milk fell into neglect, and, even after the revival of letters in the sixteenth century, still remained obscure.

The discovery of micro-organisms in perishable products, which is attributable to Anthony Van Leeuwenhoek, a Dutchman, whose vocation was the polishing of lenses, and who lived between 1632 and 1723, altered our point of view, not only of disease, but of all the functions carried on by the lower organisms. Since Van Leeuwenhoek's time, the germ theory has grown to vast proportions and has more especially been applied with splendid results to the study of milk. As we shall see later, the researches of modern investigators have led them to the conclusion that micro-organisms play such an important part in the milk supply, that it is impossible to carry it on safely without a knowledge of the bacteriology of the subject. This view began to prevail about 1890, some twenty years after Pasteur had shown what fermentation really meant. Since that time, the progress in dairying has been continuous, and, during recent years, attention has been directed to soured milk to such an extent that it has become necessary for all who are interested in the handling of milk and milk products to have a knowledge of the subject, as it seems clearly demonstrated that, under proper direction, there is every possibility of its forming an important element in the prolongation of life.

CHAPTER II

FERMENTED MILKS

There is considerable variety in the number of soured or fermented milks, and they are known by various names, such as Koumiss or Koomiss, which is prepared from mares' milk; Keffir, which was originally discovered in the mountains of the Caucasus, and which is prepared with Keffir grains; Leben, an Egyptian product prepared from the milk of the buffalo, cow, or goat; Matzoon, a soured milk which is prepared in Armenia from ordinary cows' milk; Dadhi, an Indian preparation from cows' milk. All of these owe their special characteristics to the fact of their having undergone lactic and alcoholic fermentation.

"Milk left to itself," says Blyth,[14] "at all temperatures above 90° F. begins to evolve carbon dioxide, and this is simply a sign and result of fermentation. If this fermentation is arrested or prevented, the fluid remains perfectly sweet and good for an indefinite time. Besides the production of carbon dioxide during decomposition, a certain portion of milk sugar is converted into lactic acid, some of the casein and albumen are broken up into simpler constituents, and a small proportion of alcohol produced, which by oxidation appears as acetic acid, while the fat is in part separated into free fatty acids, which ultimately unite with the ammonia produced by the breaking up of the albuminoids. The main fermentation of milk is a special kind which of late years has been much studied, and is known as lactic fermentation. Accompanying lactic fermentation there is nearly always a weak butyric and a weak alcoholic fermentation."

One of the organisms causing Butyric Acid Fermentation is a bacillus 3 to 10µ in length, and about 1µ in breadth. It has power of movement, and when cultivated in gelatine, liquefies the gelatine, forming a scum on the surface. When the bacillus is sown into sterile milk, the following, according to Hueppe, are the changes:

"If the milk thus infected is incubated, on the second day a clear, slightly yellow fluid is seen under the layer of cream; this fluid increases from day to day, so that gradually a column of fluid is formed which is quite clear above, but below is turbid; the casein, at first thrown down in a firm coagulum, in the course of eight days begins to be attacked, and by the end of two or three weeks most of it is dissolved. The filtered fluid gives the biuret reaction; it contains leucin, tyrosin, and ammonia; hence it is clear that the ferment acts to some extent as a digestive of albumen. In advanced butyric acid fermentation, the fluid is most offensive, and may have an alkaline reaction."

Lactic acid was first isolated by Scheele in 1780 from soured milk, but its exact constitution was not determined until later by Liebig, Mitscherlich, Gay-Lussac, and Pelouze: "It is widely distributed in nature, occurring in the sap of the vine and in most fermented liquids, especially in soured milk; it is not, however, present in fresh milk."[15]

In all the Eastern preparations referred to, the lactic fermentation is produced, followed by alcoholic fermentation, which is due to the slow decomposition of the milk sugar, the vinous fermentation being most readily set up in milks which contain a larger relative proportion of milk sugar and water, such as the milk derived from the mare, the sheep, and the camel. As these fermented milks have different characteristics, it is necessary to the thorough understanding of the process of manufacture at the present day, to examine them in some detail.

Koumiss.—The greatest of all the fermented milks is koumiss, and it has been celebrated from the most ancient times until the present day, as being the principal food of the wandering tribes of Khirgiz, Bashkirs, Kalmucks, and Tartars, who inhabit the steppes of European Russia and the plains of South, Western, and Central Asia. According to Carrick, who has written an interesting volume on the subject,[16] the nomads who inhabit these vast territories are shut up under the most miserable circumstances during the winter time and at the advent of spring they roam over the steppes from morning to night, usually in the saddle. The milk yielded at such time by the mares is carefully collected, and these nomads consume enormous quantities of it in the fermented state, this habit having been in existence amongst them from time immemorial. It is said that the Scythians, long before the Christian era, used fermented mares' milk; and there are ornaments in existence in Russia, of Scythian origin, which exhibit in detail the preparation of koumiss from mares' milk. In historical times, the first mention of koumiss was in the twelfth century, when it is referred to in the Ipatof Chronicles. During the thirteenth century William de Rubruquis, a French missionary, wrote about his travels in Tartary, and he described how he had first become acquainted with koumiss, and how he found it savoury to the palate. Subsequent to this, however, there is very little mention of koumiss in Russian history, or, for that matter, in any other, and the first really scientific contribution on the subject was by Dr. John Grieve, who was a surgeon in the Russian army, and who in the year 1784 sent a description of koumiss to the Royal Society of Edinburgh,[17] of which he was a member, and the title of it was, "An Account of the Method of Making Wine called by the Tartars Koumiss, with Observations on its Use as a Medicine." Dr. Grieve strongly advocated the use of koumiss as beneficial in cases of wasting diseases, and subsequently it was adopted by the medical profession, with the result that sanatoria for the treatment of pulmonary consumption were established at Samara and other places in Russia, and met with very great success; and at the present day such sanatoria are carried on, but the bacteriology of the subject now being thoroughly understood, the methods of preparation have been somewhat modified.

An interesting account of koumiss is given by Clarke,[18] who says:

"Everybody has heard of koumiss, and the brandy which the Kalmucks are said to distil from the milk of mares. The manner of preparing these liquids has been differently related, and perhaps is not always the same. They assured us that the brandy was merely distilled from buttermilk. The milk which they collect overnight is churned in the morning into butter; and the buttermilk is distilled over a fire made with the dung of their cattle, particularly the dromedary, which makes a steady and clear fire like peat. But other accounts have been given both of the koumiss and the brandy. It has been usual to confound them, and to consider the koumiss as their appellation for the brandy so obtained. By other information I could gain, not only here, but in many other camps which we afterwards visited, they are different modifications of the same thing although different liquors; the koumiss being a kind of sour milk, like that so much used by the Laplanders called pina, and which has undergone, in a certain degree, the vinous fermentation; and the brandy an ardent spirit obtained from koumiss by distillation. In making koumiss they sometimes employ the milk of cows, but never if mares' milk can be had, as the koumiss from the latter yields three times as much brandy as that made from cows' milk.

"The manner of preparing the koumiss is, by combining one sixth part of warm water with any given quantity of warm mares' milk. To these they add, as a leaven, a little old koumiss, and agitate the mass till fermentation ensues. To produce the vinous fermentation, artificial heat and more agitation is sometimes necessary. This affords what is called koumiss. The subsequent process of distillation afterwards obtains an ardent spirit from the koumiss. They call it vina. In their own language it bears the very remarkable appellation of rack and racky, doubtless nearly allied to the names of our East India spirit rack and arrack. We brought away a quart bottle of it, and considered it very weak bad brandy, not unlike the common spirit distilled by the Swedes and other northern nations. Some of their women were busy making it in an adjoining tent. The simplicity of the operation and their machinery was very characteristic of the antiquity of this chemical process. Their still was constructed of mud, or very coarse clay; and for the neck of the retort they employed a cane. The receiver of the still was entirely covered by a coating of wet clay. The brandy had already passed over. The woman who had the management of the distillery, wishing to give us a taste of the spirit, thrust a stick, with a small tuft of camel's hair at its end, through the external covering of clay, and thus collecting a small quantity of the brandy, she drew out the stick, dropped a portion on the retort, and, waving the instrument above her head, scattered the remaining liquor in the air. I asked the meaning of this ceremony, and was answered that it is a religious custom to give always the first drop of the brandy which they draw from the receiver to their God. The stick having been plunged into the receiver again, she squeezed it into the palm of her dirty and greasy hand, and after tasting the liquor, presented it to our lips."

Another interesting account of the preparation of koumiss is given by John M. Wilson in the Rural Encyclopædia,[19] and it shows that the methods in use about the middle of last century did not differ materially from those which existed centuries before.

Wilson says: "Khoumese is vinously fermented mares' milk. Any quantity of fresh mares' milk is put into wooden vessels; a sixth part of water just off the boil is mixed with it; an eighth part of old khoumese or of the sourest possible cows' milk is added; the mixture is kept from fifteen to twenty-four hours, covered up with several folds of coarse linen cloth and with a very thick board, and without being stirred or in any degree disturbed, in a moderately warm place till it becomes thoroughly sour, and sends up a thick mass to its surface; it is then beaten and pounded and stirred till the curd is not only broken, but so thoroughly mixed with the serum as to form a thick liquid; it next remains covered and at rest during twenty-four hours more, and it is finally put into a common butter churn and beaten and blended into a state of perfect homogeneity. It is now fit for use; yet it acquires an increase of given properties if it be allowed to stand for a few days, and either then or now it would, if distilled, yield nearly one third of its own bulk of a weak spirit which will bear to be rectified. Whenever it is used it must be previously so agitated that its component parts may be well mixed together, and it may be kept either in pans for immediate use or in casks for more remote use; and if placed in a cool cellar it will remain good during three or four months."

Mares' milk owes its peculiar fitness for making koumiss to its containing a large proportion of sugar of milk, and readily undergoing the vinous fermentation, and it possesses a general medicinal reputation among the Tartars similar to that which asses' milk has partially acquired in Britain. "That mares' milk will undergo vinous fermentation and yield a certain quantity of spirit," says a writer in the Magazine of Domestic Economy, "is not generally known, and it was reserved for a nation of demi-savages to render this circumstance available as an agent of health, as well as an agreeable and nourishing beverage. Every educated person, however, has heard that the Tartars drink mares' milk, though few know that this milk is taken on account of its specific virtues alone, and not as a substitute for cows' milk, of which they have abundance, and with which they adulterate mares' milk when scarce." But the koumiss is reputed to be much more medicinal than the mares' milk itself; and on account of its being free from all tendency to curdle in the stomach, and of its possessing most of the nutritive power of the milk in combination with native fermented spirit, it has been strongly recommended by some persons as a remedy for most or all cases of general debility, of nervous languor, and even pulmonary disease.

"Khoumese is called sometimes koumiss and sometimes milk wine."

From these references it will be seen that koumiss is an alcoholic drink made by the fermentation of mares' milk, but it is also frequently prepared from the milk of the camel and cows' milk. It is stated that a similar preparation to Russian koumiss is made in Switzerland from cows' milk simply by the addition of a little sugar and yeast to skim milk; "it contains more sugar and less lactic acid than Russian koumiss, and on account of the much greater proportion of casein contained in cows' milk, differs considerably from that prepared from mares' milk." Suter-Naef gives the composition of a Swiss koumiss[20] manufactured at Davos as follows:

The ferments used in the preparation of koumiss are stated by Carrick to be of two different kinds, artificial and natural.

"Of the natural ferments two have been resorted to. One is mentioned by Grieve, which he borrowed from the Bashkirs of Orenbourg, and which simply consists in the addition of one sixth part of water and one eighth of the sourest cows' milk to fresh mares' milk; the other has been employed, and was, if I mistake not, first recommended by Bogoyavlensky. It is a very simple if rather a tedious method. New mares' milk, diluted with one third its bulk of water, is placed in the saba,[21] and while allowed to sour spontaneously, is continually beaten up. This milk gradually undergoes the vinous fermentation, and in twenty-four hours is converted into weak koumiss. The disadvantage of this mode of commencing fermentation is obvious—viz., the great waste of time in agitation. Hence it is only employed when no artificial ferment is obtainable.

"In starting the process of fermentation in mares' or any other kind of milk, therefore, an artificial ferment is more frequently employed than a natural one. The former is used only for converting the first portion of milk into koumiss; the latter is always resorted to afterwards.

"Of artificial ferments the variety is great, for besides all putrefying animal matters which contain nitrogen—such as blood, white of egg, glue, and flesh—certain mineral substances which act by souring the milk are also capable of exciting fermentation.

"Now, many of the nomads, whose mares either give no milk or are not milked in winter, commence the preparation of their koumiss in spring by borrowing a ferment from the animal, mineral, or vegetable kingdom. Thus a mixture of honey and flour is the favourite ferment with some races of nomads; a piece of fresh horse-skin or tendon is preferred by others, while a few resort to old copper coins, covered with verdigris, for starting fermentation. In the choice of a ferment they are guided solely by habit and tradition. As it would be useless, almost impossible, to give a list of all the foreign substances that have been employed with the view of converting mares' milk into koumiss, it will be best to consider the simplest artificial ferments, and those most generally in use.

"The simplest way is that recommended by Bogoyavlensky, and adopted and modified by Tchembulatof.[22] It is prepared thus: 'Take a quarter of a pound of millet-flour, add water to it, and boil it down to the consistence of thick oatmeal porridge. Then heat separately, in another vessel, eleven pints of milk to boiling-point, and allow it to cool down. When its temperature has fallen to 95° F., pour it into a wooden bowl or tub, and add the boiled flour to it. The upper and open part of the vessel is then covered with a piece of coarse linen, and left at rest—at a temperature of about 99° F.—from twenty-four to forty-eight hours. The appearance of small bubbles, which keep bursting on the surface of this liquid, combined with a vinous or acid odour, prove that the ferment is ready. To this fermenting fluid twenty-two quarts of new milk are gradually (i.e., every ten minutes) added, and the whole mass is continuously beaten up for twelve hours. The temperature during stirring should never be higher than 94° F. The whole fluid soon begins to ferment, and after twelve hours a not unpleasant koumiss is ready. This should be filtered through a horse-hair or muslin sieve, after which it is fit for drinking. This liquid is called weak koumiss; but a limited portion of the lactine has undergone the lactuous and vinous fermentations, and thus the percentage of alcohol is small. Koumiss at an ordinary temperature remains weak for twelve hours after it has been beaten up, and then gradually passes into medium.'"

Curiously enough, the richness of cows' milk in fat militates against its being a good raw material for the making of koumiss, owing to the production of small quantities of butyric acid, which follows upon the fermentation, so that it is desirable, if koumiss is to be prepared from cows' milk, that the fat should be first of all eliminated, so that the separated milk will then approximate to the composition of mares' milk.

"The chemical changes," says Hutchison,[23] "which take place in the milk under the double fermentation are not difficult to follow; the lactic ferment simply changes part of the sugar into lactic acid, the vinous ferment eats up a very small part of the proteid of the milk, and, at the same time, produces from the sugar a little alcohol and a good deal of carbon dioxide; the milk thus becomes sour, it effervesces and is weakly alcoholic, but the lactic acid causes the casein to be precipitated just as it does in the ordinary souring of milk, and the casein falls down in flocculi."

As will have been noticed, it is an essential part of the process of koumiss-making to keep the milk in a state of agitation during the period of fermentation, a process which is intended to permit of oxygen being taken up by the fermenting fluid, while, at the same time, the casein is broken up into a state of fine division. The casein also, or at least a portion of it, becomes very soluble, and after twelve hours of fermentation the taste of the product is only slightly sour, and the milk taste still remains. This taste, however, disappears in twenty-four hours, owing to the rapid development of the lactic acid organisms. After this lapse of time the sugar is entirely destroyed, and the strong koumiss which results is a thin sour fluid which effervesces briskly, and in this condition will keep for an indefinite period. "The net change which has taken place in the original milk may be summed up by saying that the sugar of the milk has been replaced by lactic acid, alcohol, and carbon dioxide, the casein has been partly precipitated in a state of very fine division, and partly pre-digested and dissolved, while the fat and salts have been left much as they were."[24]

Violent stirring or agitation of the cultures does not seem to work so much by supplying oxygen to the fermenting liquid, as by ensuring a thorough distribution of the micro-organisms throughout the liquid, and thus dividing the casein.

The greater number of the organisms are facultative anærobes and oxygen is not necessary. Again, koumiss put up in bottles on the first day is regularly shaken although air is excluded.

Keffir.—Keffir is a kind of fermented milk which has been in use in the Caucasus for quite a long time, as koumiss has been in the steppes. It differs from koumiss, however, in this respect, that it is prepared from either sheep's, goats', or cows' milk. The process is started by the addition of keffir grains to the milk, which is contained in leathern bottles. These keffir grains are small solid kernels which are kept in families and handed on from one generation to another.[25] The grains are the origin of the ferment, as they disseminate in the milk micro-organisms of a lactic yeast (Saccharomyces kefir Beyerinck and Freudenreich) and also the bacillus Bacterium caucasicum, which develop rapidly and split up the milk sugar into carbon dioxide, alcohol, and lactic acid. Small quantities of glycerine, acetic, succinic, and butyric acids are also formed, the casein and albumen being partly peptonised.[26] Keffir becomes slightly effervescent in twenty-four hours, and in that time develops a small quantity of alcohol, but after three days the amount of alcohol and lactic acid is much increased.[27] It has been determined that the fermentation of the milk is due to Saccharomyces kefir, and that the Lactobacillus Caucasicus does not take any part in the fermentation, a fact which seems to be supported by the capacity of ordinary keffir for starting the fermentation in fresh milk in the same manner as the keffir grains. The use of this beverage seems to be universal throughout the Caucasus, and travellers in these regions have frequently referred to it. Thus Freshfield[28] states in one part of his book of travels as follows:

"The pig-faced peasant against whom we had at first sight conceived such an unjust prejudice turned out a capital fellow. He brought us not only fresh milk, but a peculiar species of liquor, something between public-house beer and sour cider, for which we expressed the greatest admiration, taking care at the same time privately to empty out the vessel containing it, on the first opportunity." And again:

"The hospitable shepherds regaled us, not only with the inevitable and universal airam or sour milk—if a man cannot reconcile himself to sour milk, he is not fit for the Caucasus—but with a local delicacy that has lately been brought to the knowledge of Europe—kefir. This may best be described as 'effervescing milk.' It is obtained by putting into the liquid some yellow grains, parts of a mushroom which contains a bacillus known to science as Dispora caucasia. The action of the grains is to decompose the sugar in the milk, and to produce carbonic acid and alcohol. The grains multiply indefinitely in the milk; when dried they can be preserved and kept for future use; its results on the digestion are frequently unsatisfactory, as one of my companions learnt to his cost."

"It has been supposed," says Metchnikoff, "that the chief merit of kephir was that it was more easy to digest than milk, as some of its casein is dissolved in the process of fermentation. Kephir, in fact, was supposed to be partly digested milk. This view has not been confirmed. Professor Hayem thinks that the good effects of kephir are due to the presence of alcoholic acid, which replaces the acid of the stomach and has an antiseptic effect. The experiments of M. Rovigh, which I speak of in The Nature of Man, have confirmed the latter fact, which now may be taken as certain. The action of kephir in preventing intestinal putrefaction depends on the lactic acid bacillus which it contains. Kephir, although in some cases certainly beneficial, cannot be recommended for the prolonged use necessary, if intestinal putrefaction is to be overcome.... Professor Hayem prohibits its use in the case of persons in whom food is retained for long in the stomach. When it is retained in the stomach, kephir goes on fermenting, and there are developed in the contents butyric and acetic acids, which aggravate the digestive disturbances. Kephir is produced by combined lactic and alcoholic fermentations ... and it is the lactic and not the alcoholic fermentation on which the valuable properties of kephir depend; it is correct to replace it by sour milk, that contains either no alcohol or merely the smallest traces of it. The fact that so many races make sour milk and use it copiously is an excellent testimony of its usefulness."

There are two methods given by Flügge[29] for the preparation of keffir:

"In the first, the dry brown kefir grains of commerce are allowed to lie in water for five or six hours until they swell; they are then carefully washed and placed in fresh milk, which should be changed once or twice a day until the grains become pure white in colour and when placed in fresh milk, quickly mount to the surface—twenty to thirty minutes. One litre of milk is then poured into a flask, and a full tablespoonful of the prepared körner added to it. This is allowed to stand open for five to eight hours; the flask is then closed and kept at 18° C. It should be shaken every two hours. At the end of twenty-four hours the milk is poured through a fine sieve into another flask, which must not be more than four fifths full. This is corked and allowed to stand, being shaken from time to time. At the end of twenty-four hours a drink is obtained which contains but little carbon-dioxide or alcohol. Usually it is not drunk until the second day, when, upon standing, two layers are formed, the lower milky, translucent; and the upper containing fine flakes of casein. When shaken it has a cream-like consistence. On the third day it again becomes thin and very acid. The second method is used when one has a good kefir and two or three days to start with. Three or four parts of fresh cows' milk are added to one part of this and poured into flasks which are allowed to stand for forty-eight hours with occasional shaking. When the drink is ready for use, a portion (one fifth to one third) is left in the flask as ferment for a fresh quantity of milk. The temperature should be maintained at about 18° C., but at the commencement a higher temperature is desirable. The grains should be carefully cleaned from time to time and broken up to the size of peas. The clean grains may be dried upon blotting-paper, in the sun, or in the vicinity of a stove; when dried in the air they retain their power to germinate for a long time."

Leben.—In our earlier references to fermented milks in scriptural times, we observed that alcoholic fermented milks were not permitted to be presented at the altar. Such offerings, however, were quite allowable amongst the ancient Egyptians, the Arabs and Carthaginians,[30] and from remote antiquity these nations placed great value on this product. Leben, which is peculiarly associated with Egypt, is a soured milk prepared from the milk of buffaloes, cows, or goats. It is usually prepared by the boiling of the fresh milk over a slow fire, after which some fermented milk from a previous preparation is added to the warm article, and the fermentation takes place rapidly and is considered to be complete in about six hours.[31] The Egyptian leben is valued so highly that it is offered in hospitality to the passing stranger, and it is regarded as so much of a duty to present this milk, that in some parts of Arabia it would be looked upon as scandalous if any payment were received in return.[32]

Matzoon.—Matzoon is prepared in Armenia in somewhat the same manner as keffir is prepared in the Caucasus, and indeed it differs very slightly from keffir in composition. Its use is universal in Armenia.

Dadhi.—In India large quantities of fermented milk are used, under the name of Dadhi, and its characteristics are not unlike the similar products in Europe. The specific bacillus has been investigated by Chatterjee,[33] who concludes that it is somewhat akin to the Bacillus bulgaricus and the bacillus of leben (B. lebenis). Dr. Chatterjee gives a résumé of his investigations which sums up the whole matter thus:

"1. The fermented milk of India called Dadhi resembles in all essential points the Bulgarian fermented milk as well as the leben and other forms of fermented milk in use in the East.

"2. The causative element of the curdling process of Dadhi is a streptothrix having characters similar to the Bacillus bulgaricus and Streptobacilli lebeni, and Bacillus caucasina and the Long Bacilli of Mazun, in (1) not growing in ordinary media; (2) producing a large amount of lactic acid in milk; (3) producing, besides coagulation of casein and splitting up the sugar of milk into lactic acid, no other change in milk; (4) not producing any indol, nor peptone, nor saponification of fat, nor formation of any gas.

"3. It differs from the above by showing peculiar pink-stained granules, when stained with methylene blue and showing peculiarly convoluted chains in glucose agar.

"4. The importance of the organism lies in the fact that, as in the case of Bacillus bulgaricus, it kills all pathogenic non-sporing germs and also destroys all proteolytic gas-forming bacilli in milk."

In the account of these investigations the following table is given, showing the amount of lactic acid produced by different lactic acid bacilli in one litre of milk, in terms of lactic acid—the culture being kept at 37° C.

In different parts of the world sour milk is consumed in great quantities, and it is stated by Metchnikoff[35] that the chief food of the natives of tropical Africa consists of soured milk, and in Western Africa in the region south of Angola, the natives live almost entirely on this product, there being a difference in the curdled milks produced according to the nature of the microbial flora which is introduced.

It is stated[36] that in Servia, Bulgaria,[37] and Roumania there were 5000 centenarians living in 1896, and while many reasons are advanced for such an abnormal condition of affairs, it seems fairly certain that the sole reason why people in these districts live to such great ages is because of their mode of living and the fact that they live very largely on soured milk. The hygienic conditions throughout these countries are not such as would give the population in the towns and villages any special advantages in the prolongation of life, and while it may be stated that a pastoral and agricultural life are likely to contribute to longevity, these conditions would not account for a general tendency to live long in the countries referred to, more than in any other agricultural area. There are many countries throughout the world in which the pastoral and agricultural existence is general, but it has not been shown that in these countries life is prolonged. Hence the conclusion has been forced upon investigators that the reason is to be found not in the pastoral conditions, but in the habit which has existed from time immemorial of consuming sour milk as a principal article of diet.

There is no curtailment of the use of fermented milks in Eastern Europe, and the methods of preparation at the present day are those which have been carried out from time immemorial. A local observer states that in Bulgaria yoghourt is made in nearly every household, especially in the spring and summer. The method of preparation is very simple: The milk is boiled until a quarter of its volume has evaporated, it is then cooled to 45° C. and the ferment added. This ferment is a portion of the yoghourt of good flavour and is called "Maya" or "Zakvaska." The vases, a kind of earthenware pot, are enveloped in woollen stuff or sheepskin and placed in a warm place near the chimney. In ten hours the yoghourt is made, and it is preserved in a cold place. The great reputation that the yoghourt has acquired in Western Europe has caused this "Maya" to become an article of commerce. It is sent out by rail hermetically sealed in tinplate boxes. According to a Sophia chemist, the "Maya" is employed in the following manner: For a litre of milk it is necessary to take about 10 gr. of the ferment. This ferment is diluted with three times the amount of water and put into a bowl previously heated with hot water and dried. Into this bowl the milk, previously boiled and cooled to a temperature of 75° to 50° C., is poured; it is then covered over and put in a temperature of about 30° C., and, in default of a stove of constant temperature, the bowl is wrapped round with flannel or a plaid, and left to curdle for eight to ten hours. It is then ready for consumption. During winter, curdled milk keeps for several days, and in summer it becomes sour in from twelve to twenty-four hours.

A similar food to the yoghourt is prepared in the Balkan mountains from sheep's milk under the name of "Urgoutnik."[38] The milk is poured into a goatskin or sheepskin bag, and a little of the fermented milk added, and is then left for some hours in a warm place. The milk consumed is replaced by a fresh supply. In some of the Balkan countries, they are not content with the fermentation of the milk, they add a little alum, which, under the name of "typsa," is well known for this purpose. The milk attains such a solid consistency that it can be put into a cloth and carried to market.[39]

The various forms of sour milk which have been described in the foregoing pages may be said to be of the traditional kind, and with the light of modern knowledge, it has been possible to determine exactly what constitutes the active principle in use in the milk consumed in these countries, and, as we shall see, this principle has been applied so that, at the present day, a pure fermented milk may be obtained in any country, and there is every reason to believe that should such be adopted as a general article of food, it would contribute to the prolongation of human existence.

It is due to Metchnikoff, of the Pasteur Institute, that so much prominence has been given to the use of fermented milks. He gave it as his opinion[40] that senility was caused partly by auto-intoxication or by the poison derived from putrefactive micro-organisms which inhabit the digestive track. These organisms increase with age, and under certain unhealthy conditions multiply enormously, particularly in the large intestine. Having arrived at this knowledge, Metchnikoff set to work to devise some means of combating the influence of these harmful microbes, and set up the hypothesis that the tendency to longevity which is exhibited in Eastern countries is due to the consumption of lactic acid organisms in the shape of soured milk. These organisms are more powerful than those of a putrefactive character and inhibit their growth.

"In the presence of such facts," says Metchnikoff, "it becomes exceedingly important to find some means of combating the intestinal putrefaction which constitutes so incontestable a source of danger. Such putrefaction is not only capable of producing diseases of the digestive tube—enteritis and colitis—but even of becoming a source of intoxication of the organism in its most varied manifestations.

"It is some years since I proposed to combat intestinal putrefaction and its injurious consequences by means of lactic ferments. I thought the acidity produced by such microbes would be much more effective in preventing the germination of putrefying microbes than the small quantity of acids produced by Bacillus coli. On the other hand, I had no illusion as to the difficulty sure to be encountered in any effort to introduce lactic microbes into the intestinal flora which has been preoccupied by a multitude of other microbes. To make surer of the result, I chose the lactic microbe, which is the strongest as an acid producer. It is found in the yahourt (yoghourt), which originates in Bulgaria. The same bacillus has also been isolated from the leben of Egypt; and it is now proved that it is found in the curdled milk of the whole Balkan peninsula, and even in the Don region of Russia."[41]

It is a short step from considerations like these to the adoption of the Bacillus bulgaricus as the most potent of the various lactic organisms which have been examined, and which is likely to play such an important rôle in the destiny of the human race. The Bacillus bulgaricus may claim to be the Bacillus of Long Life.

CHAPTER III

THE CHEMISTRY OF MILK

The Composition of Milk.—Like all other organic substances, or those built up in connection with the life processes of plants and animals, milk is of complex composition. It is also very liable to change—every one is acquainted with its tendency to "go bad." This instability is more or less inherent in all highly organised chemical compounds, and, indeed, it seems to be necessary that the materials used in growth and nutrition should be very plastic in a chemical sense, in order, e.g., that the constituents, say of a plant, may easily be transformed into the substances of the body of the animal which feeds on it.

The perishable nature of milk—the food of young and growing animals—is therefore essential, so that it may be changed easily into the blood, bone, muscle, etc., so abundantly required in the early stages of existence.

Milk is a complete food, and, therefore, naturally it is not a simple chemical compound, but a mechanical mixture of a number of substances. The present state of chemical knowledge on the subject does not permit of its composition being given in detail, but for practical purposes, such as those of measuring its purity and food value, this is not necessary.

A proximate analysis, in which, at least, some of the ingredients are lumped together, is sufficient, and has been adopted everywhere by analysts. On this basis the average composition of cows' milk may be stated as follows:

The constituents other than water added together form the "total solids," and they amount to 12.5 per cent.

The Constituents of Milk

In the illustration, a pint of milk is shown in a glass jar, and the various percentages of water, casein, sugar, ash, albumen, and fat, which make up its constituent parts, are shown in separate bottles, the percentage of each being stated beneath.

Milk varies a good deal in composition; the different breeds of cows give varying qualities. The Short-horn gives large quantities of milk of rather poor analysis, while the Jersey yields smaller proportions of very rich milk. During the period of lactation (the time which has elapsed since the cow gave birth to a calf), care in milking, food, health, etc., all have an effect on the quality of the milk.

The limits of variation may be stated as follows:

These figures are extreme, and it is very seldom indeed that either the minimum or maximum is reached. Indeed, by the regulation laid down under Clause 4 of the British Sale of Food and Drugs Act of 1899, when the percentage of solids not fat falls below 8.5 per cent., and fat under 3 per cent., it is assumed that the milk has been adulterated. This regulation is a perfectly just one. While genuine milk may, in rare instances, show figures as low as 7.1 per cent. of solids not fat, or 2.5 per cent. of fat, the right can hardly be claimed of supplying such an abnormal article to the public as milk of proper quality, and the dairyman who understands his business, and wishes to deal fairly with his customers, can, by attention to the conditions enumerated above which influence the composition of milk, entirely avoid the production of such a low-grade article.

In the nutrition of both plants and animals large quantities of water are needed. The solids must be supplied in solution or dissolved in the assimilative processes, and this cannot take place without water, which also conveys the dissolved solids to the various parts of the economy, and in the case of animals removes waste materials. For the most part, water passes through the body unchanged, but a certain proportion unites chemically with the food materials and assists in their digestion. It is therefore not surprising that seven eighths of milk is composed of water. Blood contains a similar proportion, and this agreement emphasises the fact that milk is a perfectly balanced food.

The fat of milk, which yields cream and butter, differs in some important respects from other fats. Like these, it is made up chiefly of stearin, palmitin, and olein, but, in addition, it contains an abnormally large proportion of compounds of certain of the volatile fatty acids. It is these which give to butter its agreeable flavour. By the methods of Duclaux, the following is the approximate composition of butter fat:

Myristin occurs in nutmegs; butyrin in another combination flavours pineapples and rum; caprinin is found in cocoanut fat, mutton fat, and in the offensive odour given off by the goat (from which the name is derived); caprylin is a by-product of alcoholic fermentation, and also occurs in cocoa fat; laurin is found in sweet bay; from which it is evident that there are some curious relationships in flavouring materials.

Fats are very concentrated foods, furnishing a large amount of energy to the body. At one time they were classed together with starch, sugar, and other carbohydrates as heat-producers, but the distinction which was drawn between the kinds of food which were thought solely to keep up the temperature of the organism, and those which produced force in work and other forms of bodily energy, has broken down, and by direct experiment has been found not to exist. It is usually calculated that one part of fat is equal in food value to about two and a quarter parts of any of the other carbohydrates. Milk fat or butter is more digestible than almost any other fat, and its importance therefore can readily be realised. All the above constituents of milk fat are composed of different proportions of carbon, hydrogen, and oxygen, but milk also contains minute quantities of lecithin, a fat containing phosphorus in addition. Lecithin is also found in the brain and nerve material of animals, in the yolk of egg, and in several plants.

The nitrogenous constituents of milk—casein and albumen—are usually estimated together, and they are reckoned as of equivalent food value. The name protein is very commonly applied to the total of these bodies in milk, or other animal and vegetable foods. They are composed of different proportions of carbon, hydrogen, oxygen, and nitrogen, with small quantities of sulphur, while casein contains phosphorus in addition. Albumen exists to the extent of about 0.6 per cent. in milk. It is very similar in properties to egg albumen. The coagulum which forms on the surface of milk when boiled is largely composed of albumen. Casein is combined with, and kept in solution by, lime, soda, and calcium phosphate, and its amount averages a little over 3 per cent.

The remarkable property possessed by rennet, of curdling or coagulating casein, is well known; rennet is an extract from the stomach of the calf, and similar principles are present in the stomachs of man and other animals, so that the coagulation of milk is the first process in its digestion. If milk is gulped down in large quantities it is apt to coagulate in lumps, and digestion is much interfered with, but if it is taken hot and slowly, it coagulates in small pieces which are readily attacked by the gastric juice, and milk is then one of the most assimilable of foods.

Nature provides that the milk for young animals is supplied in finely divided streams, so that coagulation takes place in the best possible way.

The proteids are the most important constituents of food; they are abundant in the blood, and build up the muscles, brain, nerves, and other bodily structures.

Besides these mentioned, milk contains traces of another proteid of similar composition called globulin.

The sugar of milk is not found anywhere else. It is a carbohydrate like cane and grape sugar—that is to say, the hydrogen and oxygen they contain are in the same relative proportions as in water. Milk sugar is not so soluble or so sweet as the other sugars. It does not ferment with ordinary yeast, but certain special yeasts which are made use of in the preparation of keffir, koumiss, etc., have the power of transforming it into alcohol. Its most remarkable property, however, is the facility with which, under the influence of certain bacteria, it is changed into lactic acid.

Every one is familiar with the souring of milk, but perhaps it is not so generally known that there are great differences in the results obtained in accordance with the conditions under which the souring takes place. The skilled butter-maker, by keeping the milk in a cool and cleanly dairy, obtains a sour milk of a characteristic and agreeable aroma and taste, which beneficially affect the flavour of the butter produced. On the other hand, if milk is kept in hot and dirty surroundings, the development of acidity is accompanied by different bad tastes and odours, and it becomes unfit for use as a food. In the first case, the conditions are favourable to the maximum production of the lactic acid bacteria, and these occupy the field, and largely prevent the development of the other bacteria which are present—the survival of the fittest in the struggle for existence. In the second case, the impure surroundings swarm with the germs of many kinds of putrefactive bacteria, and the high temperature assists these to gain the upper hand. Again, the survival of the fittest, in the particular conditions. Even in cool and cleanly surroundings injurious taints may develop, especially if the milk has previously been subjected to a journey by road or rail, as is the case in the modern creamery system, where the farmers deliver their milk to a central creamery, where it is made into butter. In such establishments it is the regular practice to kill the germs, lactic and others, existing in the milk, by heating it to a high temperature. This process is called pasteurising, after the great French chemist and bacteriologist who invented it. Pure lactic cultures are added to the pasteurised milk, and the souring process is under exact control, with the result that butter of uniform flavour and quality is produced. The same method is made use of in making the special sour milk described in this book, with, of course, modifications in the apparatus employed, to suit the smaller scale in which the manufacture is conducted.

The ash is the mineral matter which is left when milk, previously dried, is burnt in a crucible. It is a complex mixture, and, as we have seen, it amounts to about 0.7 per cent. of the milk. The process of burning destroys all the organic matter, and, at the same time, alters somewhat the state of combination of the inorganic or mineral elements. Attempts have been made from the analysis of the ash to reconstitute the composition of the mineral matter as it exists in the milk. The best known is that of Soldner, and the following is his calculation:

The presence of citrates will be noted in this analysis. Citric acid, which gives to lemons their acidity, and is also found in other fruits, has been proved to exist in milk to the extent of about 0.2 per cent. When alkaline or earthy citrates are burnt or oxidised in the blood, the citric acid is destroyed, and corresponding carbonates remain. No doubt the function of citrates in milk is to furnish to the body the earthy and alkaline carbonates which are required in certain of its parts.

The mineral constituents of milk have many important functions to perform in the building up and nutrition of the bodily organism. Phosphate of lime is the principal constituent of the skeleton, and the blood must be richly supplied with the alkalies, earths, and acids which are comprehended in the ash.

Milk contains traces of many other substances, the most important of which are several enzymes which assist in its digestion.

General Properties of Milk.—The appearance of milk is known to every one; it ought to be a pure white opaque liquid, but very generally it is tinted a cream colour with anatto to give it an added appearance of richness. The average specific gravity is about 1.031; or, to put it another way, while a gallon of pure water weighs exactly 10 lbs., a gallon of milk weighs 10 lbs. 5 oz. It freezes at 31° F. and boils at about one third of a degree higher than water.

When milk is examined under the microscope, the fat is found to be distributed through it in a multitude of minute globules varying in size from 1/16,000th to 1/25,000th part of an inch, and occasionally they are much smaller and also much larger.

Fig. 1 is a micro-photograph showing the fat globules in whole milk. Fig. 2 is a micro-photograph of separated milk, and Fig. 3 a micro-photograph of cream, all under high magnification (450 diams.); from these figures the comparative number of fat globules present may be seen.

Fig. 3.—Micro-photograph of Cream, showing agglomeration of fat globules. (Magnified 450 diams.)

Fats distributed through a watery liquid in this finely divided condition form together what is called an emulsion, in which the particles of fat are kept apart by surface tension. The specific gravity of milk fat averages 0.93, and compared with water weighing 10 lbs., a gallon of fat would weigh 9 lbs. 5 oz. It is thus considerably lighter than the other constituents, and when milk is left at rest, the fat globules gradually rise to the top and float there, forming cream. The difference in specific gravity between cream and milk is taken advantage of in the mechanical separator, now so much used, and which makes such a thorough separation between the two. Cream is an article of the most varied composition, according to the ideas of the person who produces it, but it ought to contain at least 20 per cent. of butter fat, and may be made with a much larger percentage if necessary. When cream is agitated in a particular way, as by churning, the surface tension of the particles is overcome, and they run together into a mass which forms butter.

The casein of milk is not held in solution in the ordinary sense, but in a peculiar state of suspension called the colloidal condition, practically the whole of it remaining behind when milk is filtered through clay filters.

It is this state of suspension of the casein which makes milk opaque, but the opacity is considerably increased by the emulsified fat.

The coagulation of the casein in milk by the addition of rennet has already been referred to. Acids, either mineral or organic, also precipitate it in the form of flakes. Skimmed milk is now largely used for the preparation of casein by this method, and the washed and dried precipitate is used very extensively in the arts for such varied purposes as the manufacture of billiard balls, paints, cements, etc.

The clear liquid which separates when milk is curdled with rennet is called whey, and contains the milk sugar and mineral salts. The sugar is manufactured from it on a limited scale, and is used as an ingredient in infant foods, and as a convenient medium in certain medical preparations. In Sweden a kind of cheese is made from whey, but the great bulk of it everywhere is used for feeding pigs.

The comparative composition of different varieties of milk is given in the following table:

Fig. 4 is a photograph of two Petri dishes, which have been inoculated with ordinary milk (A), and milk that has been subjected to sterilisation (B). The whitish bacterial colonies on A are due to enormous numbers of organisms, while B is quite free from such growth.
For the production of a reliable lactic food, it is essential that certain precautions as to the treatment of the milk, and the maintenance of a suitable temperature during the growth of the lactic bacteria, should be observed.
In the first place, milk immediately after extraction from the cow contains only a few organisms, but these multiply so rapidly that in a few hours the bacterial content may amount to many millions per ounce. In preparing a pure culture of any specific organism, then, care must be taken to destroy all the bacteria that have accidentally found their way into the milk, inoculating with the organisms it is desired to cultivate. This is best accomplished by heating the milk to the boiling-point of water for about thirty minutes, by which time almost all the undesirable bacteria have been killed.

The milk of the cow differs a good deal from human milk, and where the former is used for the feeding of children it is usual to add milk sugar to it, and otherwise alter it to bring its composition more in harmony with the human article. The high concentration of the milk of the reindeer and the whale is noteworthy. Perhaps this may be due to the low temperature conditions in which these animals live, necessitating strong nutriment to enable their young to make proper progress in growth and development. On the other hand, the milk of the ass is poor in quality, and probably on this account it is more readily assimilated by those of weak digestion, to whom it is sometimes recommended. Goats' milk is richer than either cow or human milk, and its nourishing properties are well known. The goat is usually free from tuberculosis and other diseases which affect the cow, and its milk is therefore a very safe article to use.

The Analysis of Milk.—While the analysis of milk can only be made by a competent chemist, there are a number of simple tests and observations by which any intelligent person can obtain

Fig. 5. The Creamometer a fair idea of its quality. The taste and smell afford some guide, as also the general appearance. To judge of the latter, place some of the milk in a tumbler or other clear glass vessel. If the milk is of good quality it will be quite homogeneous and opaque. Any flocculent matter indicates either disease in the cow or that the milk is old and bacteria have multiplied in it and altered its composition. When the milk has stood long enough for the cream to rise freely, the latter should form a perfectly homogeneous and strongly defined layer on the top. The quantity of cream may be measured in a creamometer, which consists of a small glass cylinder graduated at the top (Fig. 5). It is filled with milk to the top graduation line, and when the cream has risen, the percentage quantity of the latter which has separated can be taken off.

The colour should be like that of porcelain, but, as already stated, it is a common thing for the dairyman to add a small quantity of anatto or an aniline dye of a similar shade, to give the milk a rich creamy tint. If the milk is of a reddish colour this may be caused by blood from the udder, although certain foods, such as beets, mangels, and carrots sometimes give a similar tint. The milk given by cows immediately after calving is called "colostrum" or "biestings," and is of a yellow or yellow-brown colour. It is much thicker than ordinary milk, and coagulates in boiling.

In dirty byres in which care is not taken in milking, quite considerable quantities of hairs, pieces of manure, and other filth may get into the milk. Usually the milk is strained by the dairyman, but sometimes this is omitted or carelessly done. To test for dirt, a ribbed glass funnel is useful. Get a piece of the finest muslin about twice the diameter of the funnel, fold over twice, so that it becomes one quarter of its original size; open one of the sections and place in the funnel; pass the milk into this. It will run through quickly and some water may be run into the funnel to clear away the last traces of milk. The filter cloth can then be opened out and any dirt retained will become visible. The apparatus is shown in Fig. 6.

Testing-Glass for Extraneous Matter in Milk.

Fig. 6.—A piece of muslin is folded as shown and a measured quantity of milk is passed through the funnel; from the sediment left in the muslin, the percentage of extraneous matter may be arrived at.

If a glass funnel is not available, a very small jelly bag can be made of fine gauze and used in the same way. The washing water should be used in small quantities and directed to concentrating the dirt in the apex of the bag. After washing, the latter can be turned outside in, to permit of readier examination of the dirt. The bag should be well washed in cold water, then boiled and dried, and is then ready for future use.

The acidity of milk is a very useful guide to its age. Milk has the curious property of being "amphoteric," i.e., it is both slightly acid and slightly alkaline when fresh. As its age increases, however, so does its acidity, and at a rate varying with the temperature and moisture contents of the atmosphere in which it is placed. Old and acid milk is heavily contaminated with bacteria, a proportion of which are likely to be injurious to health.

The simplest method of testing the acidity is to procure a few little books of blue and red litmus

Fig. 7. Lactometer and Test Tube test papers, and these can be had from any philosophical instrument maker or laboratory furnisher. The strips of test paper are torn out and dipped in the milk. When the milk is quite fresh it will, owing to its amphoteric condition, change the red litmus paper slightly blue, and the blue litmus paper slightly red. Old milk changes blue litmus paper to a bright red because of its decided acidity.

The above tests do not indicate if the milk is poor or rich, but this can be determined by the lactometer, an instrument for ascertaining in a simple way the specific gravity. The lactometer is shown in Fig. 7.

It is graduated usually from 25° to 36°, corresponding to specific gravities 1.029 to 1.038. It is graduated to degrees and half degrees. Sometimes a thermometer is combined with the instrument. The specific gravity rises as the temperature is lowered and decreases with increase of temperature, so that it is important to make the test at the figure at which the lactometer was graduated, which is usually 60° F. Failing this, an allowance has to be made for higher or lower temperatures. The milk to be tested is well mixed, and placed in a deep vessel, and the lactometer placed in it, holding it at first at an angle. It stands upright and remains deeper or higher according to the specific gravity. The reading is taken on the stem at the level of the milk. As the latter is drawn up a little round the stem, about a half degree should be added on to get the true figure. Thus, if the apparent reading is 31, the true reading may be taken as 31.5. This is the average figure for good milk, corresponding to a specific gravity of 1.0315; anything above this is all to the good. Lower readings mean inferior quality, the latter being proportionate to the lowness of the readings. The tests are most conveniently made in a glass cylinder (Fig. 7), which may be purchased with the lactometer. As there are many inaccurate instruments in the market, it is necessary to go to a reputable maker, because an unreliable lactometer is worse than useless.

The following table gives, in a condensed form, the allowances to be made when the temperature is above or below the standard (60° F.):

Thus if the thermometer indicates 40° F., and the lactometer 29.1°, the true reading at the standard temperature of 60° F. is 31°, corresponding to a specific gravity of 1.031. Intermediate figures can readily be averaged. Care should be taken to wash the lactometer with cold water under the tap, as otherwise the milk will dry on it and render it inaccurate.

CHAPTER IV

HANDLING OF MILK

MODERN DAIRY PRACTICE

As we have seen, the dairy industry is a very ancient one, and has been intimately associated with the development of civilisation.

Within historical times dairying has always formed a prominent feature in connection with agriculture, and the use of milk in one form or another has been common to every civilised nation.[42]

The greatest progress, however, in the study of milk has taken place since about the year 1890, at which time the dairy industry seems to have attracted the general attention of food specialists and scientific investigators throughout the world. Since then it has been considered worth while to enact laws in different countries with regard to the regulation and control of the milk supply.

Since 1903 there has been an International Dairy Federation formed, and it has held conferences at Brussels, Paris, The Hague, and Buda-Pest, and in 1911 it will hold a conference in Stockholm. The Federation was started in a very humble way in Brussels, and owes its origin, to a large extent, to a distinguished Belgian agriculturist, Baron Peers of Oostcamp, Bruges; but at the present day a general committee composed of representatives of nearly every civilised nation has been formed, and delegates from such countries attend the Congresses, which are held every two years. The literature which has arisen out of these International Congresses has been disseminated in different countries, and has been instrumental in placing the dairy industry on a thoroughly scientific basis.

Milk Supply of the United Kingdom.—The milk supply of the United Kingdom has steadily grown from year to year, and in relation to the population works out at fifteen gallons per head. The manner in which these figures are arrived at is shown in the following estimate:

The population of the United Kingdom is now about 45,500,000. The number of cows or heifers in calf or in milk in June, 1909, was 3,360,600; the number in 1910 was probably about 4,400,000.
Of these about 300,000 were heifers that had not yet produced any milk. The actual milking class, therefore, comprised about 4,100,000 cows and heifers; of these, about 600,000 were heifers that calved in the winter and spring of 1909-10, and 300,000 were heifers that calved in the summer and autumn of 1910. The number of cows that produced two or more calves may be taken to be about 3,200,000; of these about 600,000 should have produced their second calf in the winter and spring 1909-10, and would be milked as heifers in the summer and autumn of 1910; the number of mature cows from which a full season's supply of milk was obtained during the twelve months from June 5, 1909, to June 4, 1910, was apparently about 2,600,000. A large quantity of milk is yielded during the year by cows sold or lost during the twelve months before the census. Possibly ten per cent. of the milk produced in the twelve months from June, 1909, to June, 1910, was yielded by cows that were sold or lost before the census of June, 1910.
It is estimated that the 3,200,000 cows (including the 600,000 that up to the winter of 1909-10 were heifers) produced, on the average, 44 cwts. (480 gallons) of milk per head in the twelve months from June 5, 1909, to June 4, 1910; the 300,000 heifers that calved in the summer and autumn, 30 cwts. (330 gallons) per head; the 600,000 heifers that calved in the winter and spring of 1909-10, 15 cwts. (165 gallons), making the total quantity of milk produced in the twelve months by cows and heifers on the farms, and that produced calves during the twelve months (June, 1909-1910), 158,800,000 cwts. (1,746,800,000 gallons), or about 426 gallons per head, and about 400 gallons per head for all the cows and heifers in milk or in calf in 1910. There remains to add the milk yielded by the cows that were sold during the twelve months, and of cows and heifers in feeding pastures that were milked during the twelve months, June to June, 1909-10, and which probably formed one tenth of the whole supply, making the total supply for the twelve months 176,444,000 cwts., or 1,940,884,000 gallons. This equals 2 tons, or 440 gallons per head, crediting the whole supply to the 4,400,000 cows and heifers in milk or in calf in June, 1910. At 7-1/4d. per gallon the value of milk produced in the United Kingdom in the twelve months was £58,600,000. Including the value at birth of the calves, the total value of the produce of the milk-giving class would be about £62,000,000. The value of the milk, butter, cheese, and cream sold or consumed in farmhouses would be about £48,000,000, or equal to about 24 per cent. of the gross annual income of farmers.
The average consumption of new milk is about 15 gallons per head of the population. During the twelve months of 1911, the quantity required for this purpose will be about 682,500,000 gallons, or about 35 per cent. of the total supply; calves will require about 10 per cent. of the supply; the quantity available for butter and cheese will equal about 55 per cent. of the supply. [43]

The Milk Industry in the United States.—In the United States of America, where the habits of the people are somewhat analogous to those in the United Kingdom, it is estimated that the milk from five million cows is annually consumed, which averages twenty-five and one half gallons per year for each person, or equal to an ordinary sized tumblerful each day.[44]

Such a vast industry, so intimately associated with the food of the bulk of the people, naturally invites the closest study, and, as a consequence, the literature on the subject, which has arisen during the last twenty years, has been of a voluminous character, not only from the point of view of practice, but from that of bacteriology, chemistry, and hygiene.

A pure milk supply is essential to health, and it seems unfortunate that the ordinary milk producer should, in a great many cases, take up an antagonistic attitude to the scientific methods of handling milk. There is a body of opinion being created, however, which is likely to alter this attitude in the next generation, and this is attributable to the fact that so much excellent work has been done at numerous dairy colleges and institutes in all civilised countries that the dairy industry is emerging from a period of rule-of-thumb procedure to its proper place as one of the technical arts.

Transmission of Disease in Milk.—It is not to be wondered at that the handling of milk should now be regarded as a technical business, seeing that milk-borne disease is one of the commonest with which we have to deal.

The commoner diseases which have been transmitted by milk are scarlet fever, typhoid, diphtheria, tuberculosis, sore throat epidemics. Others of a more complex character have been traced to the same source of infection, and the clearest possible evidence has been furnished of the transmission of diseases by means of micro-organisms, which have contaminated the milk supply.

It is therefore necessary to watch over the milk from the source of supply to its consumption. It is primarily on the farm and in the cow-house that methods of handling in a hygienic way should be insisted on, as microbial contamination increases at a prodigious rate, and it is the early microbe therefore which does the most damage.

The milk in the udder, for all practical purposes, may be assumed to be sterile, and the contamination which takes place originates, therefore, from external sources.

One of the principal means of infection is from hairs which fall from the cow into the milk, and many of which are carriers of dangerous micro-organisms.

There is also a certain amount of offensive dirty matter which may fall into the milk-pail, and carry with it undesirable germs.

These impurities may, to a certain extent, be eliminated by good straining, but a surer prevention is to have the cow-house perfectly clean and free from dust, as dust specks are in many cases the vehicles of disease germs. Cleanliness is, in fact, the essential feature in modern dairying, not only in the cow-house, but in the milking utensils, the drainage, etc., and, above all, the milker should be of cleanly habits.

The flavours of milk sometimes arise from the absorption of evil-smelling gases in the cow-house, or from a peculiar taint from certain roots and feeding stuffs, and in such a case it is desirable that aëration should take place in a fresh clear atmosphere, so that oxygenation may have the effect of eliminating and destroying the foreign odours and flavours which may be present. If this process of aëration is carried out at blood heat, the result is generally highly satisfactory.

Milk Management.—There have been many excellent tables of rules published for the management of dairies in different countries, but they are necessarily framed within certain limitations which apply to all. The following is an excellent set, which put concisely the conditions necessary to be observed in the modern cow-house:

1. The cow should be sound—no disease should exist in the animal.

2. The feed should be good and free from aromatic substances. If these aromatic foods are used, they should be employed according to those methods which will not cause odours or flavours to appear in the milk.

3. The cow should be groomed, and hair about the udder preferably clipped.

4. The udder should be moistened during milking.

5. The milker should be a neat, tidy person.

6. The milker should be free from disease, and should not come in contact with any communicable disease.

7. The milker's clothes and hands should be clean while milking.

8. The pail should be sterilised.

9. The stall should be such as to reduce the amount of disturbance of dust and dirt.

10. There should be good light, good ventilation, and good drainage in the cow-house.

11. The cow-house should always be kept clean.

12. Feeding and bedding, unless moist, should be done after milking.

13. A dustless milking-room is desirable.

14. Milk should not stand in the cow-house.

15. If milk is aërated, it should be done before cooling and in pure air.

16. The sooner the milk is cooled after milking the better.

17. Keep the milk as cold as possible when once cooled.[45]

The supply of milk is conducted, to a large extent, by towns' dairies, which depend for their supplies upon the dairy farm in the country, and it is obvious that a certain period of time must elapse, in the generality of cases, before a town's dairy receives its supply in the ordinary course, and this constitutes the greatest difficulty in modern dairy practice, owing to the liability of the milk to absorb bacteria, which during transit may multiply enormously.

The multiplying of bacteria in milk at different temperatures is easily demonstrated, and the result of this has been stated in various forms many times over. As a graphic means, however, of showing the increase that takes place in the numbers of germs present, and the consequent product of acidity, the table below by Conn may be given.

The consequent result of the increase in bacteria is the production of lactic acid, which produces the souring so familiar in milk which has been kept in the household at a high temperature.

Numbers of Bacteria per c.cm. in Milk kept at Different Temperatures.

What actually happens is that the lactic acid is produced by the breaking up of the milk sugar, and the appearance of this sourness is an indication that a period has been reached in the age of the milk which may be described as being—unwholesome.[46]

It is necessary, therefore, for the town's milk dairy to be equipped in such a way as to deal promptly with the milk supply.

We have seen that the milk should first of all be aërated at blood heat, so as to liberate objectionable odours, after which it should be cooled to as low a temperature as possible, by means of well water. When these operations have been performed on the farm, milk should be sent as rapidly as possible to the distributing towns' dairies, and should be transported in refrigerated waggons, cooled preferably with ice, during the journey. On arrival at the town dairy, it will be necessary to pasteurise the milk—that is to say, the milk should be heated to such a temperature as will destroy any pathogenic organisms which may be present, and the pasteurising temperature should therefore be in excess of the thermal death-point of all such organisms.

Pasteurisation owes its origin to Pasteur, and has become an adopted method throughout the dairy industry, and there are many mechanical devices termed "pasteurisers" (see Fig. 8) which are used for the carrying out of this particular operation. The form of one of these is that of a vertical jacketed cylinder with paraboloidal surface, around which steam is made to pass, so as to maintain the temperature at about 176° F. Milk is allowed to flow in at the bottom of the paraboloidal surface, and is caught by mechanical agitating arms, which revolve at a given speed, and by this action milk is distributed centrifugally over the paraboloidal surface, and is forced out by the same action, at the top of the apparatus, after being heated.

Pasteuriser

Fig. 8.—The milk enters from the bottom and circulates to the top of the inside cylinder, which is paraboloidal in construction. It is heated as it passes through the apparatus, and is discharged at the top at a temperature of 176° F.

The centrifugal action is sufficient to raise the milk some three to four feet, through a tube, and this is taken advantage of so as to cause the milk to flow over a conical cooler, described as a primary cooler, and in which water is made to circulate. As the hot milk descends over the conical cooler it gives up most of its acquired heat to the water, and, in practice, is reduced in temperature to within 4° of the temperature of the water.

Below this primary cooler is fixed a cooler of the same size and shape, which is termed a secondary cooler. In it, brine at a temperature of about 35° F. is circulated from a refrigerating machine, and, as the milk falls over the secondary cooler, it is cooled to a temperature of about 40° F., when it may be looked upon as being pasteurised and free from all pathogenic organisms, in which state it will keep for a considerable length of time.

It is desirable that the milk should, as soon as possible after the cooling takes place, be delivered to the consumers, and be kept under cool conditions, either in bottles or in a closed vessel covered over with muslin, so as to keep out specks of germ-laden dust.

Briefly speaking, the foregoing is an outline of what is carried on in the ordinary dairy practice.

There are many modifications of this practice, such as the introduction of regenerative heaters, so as to utilise a portion of the heat of pasteurisation, which would otherwise be wasted.

In some cases, again, it is considered necessary to conduct the primary and secondary cooling over coolers furnished with mantles, so that the atmospheric bacteria which are everywhere present should be shut off from the falling milk.

Ordinarily, however, the equipment for a town's dairy consists of:

1. Steam-boiler to generate steam for pasteurising, scalding, etc.

2. Motive power, which may be either a steam-engine, gas-engine, or electric motor.

3. Refrigerating machine, which is used for supplying cold brine to the secondary cooler. In many cases it is also used for cooling a room in which the milk and cream are stored.

4. Milk-receiving tank.

5. Milk-strainer.

6. Pasteurising apparatus, and primary and secondary coolers.

Such a plant is necessary in order to conduct an ordinary town dairy business in anything like a hygienic way, and is designed only for the handling of milk intended for domestic consumption.

There are times when another plant might be necessary, such as a plant for the separation of milk, or for utilising it for the production of butter or cheese, such operations being subject to the fluctuations in the milk supply.

It is sometimes desirable also to use up an excess of milk for cheese or butter-making; hence it is necessary to provide such apparatus as has been indicated.

Preparation of Soured Milk.—The foregoing description has been given in some detail, as showing the ordinary practice, and we now come to consider how it can be modified so as to provide for the production of soured milk. It may first of all be premised that within the next few years the preparation of soured milk as an ordinary production of the dairy will be universal, and will form a part of the ordinary dairy practice. The apparatus, therefore, which is necessary is one of considerable interest to all who are engaged in the dairy industry.

As will be seen from the chapter describing the preparation of soured milk in the dairy, this process can be conveniently carried on, so as to utilise the plant which is at present in general use. The milk can be received in the same way, pasteurised and cooled to about blood-heat, after which its preparation as soured milk is a very simple matter, and only requires a certain amount of careful attention.

For the keeping of soured milk, a cold room cooled by a refrigerating machine would be desirable, so as to maintain the fermented milk at a low temperature and prevent over-fermentation.

Apparatus has been designed so as to handle soured milk on a large scale, and one of the machines is shown on the illustration (see Fig. 9). It is simply a jacketed cylinder with a cover and an agitating gear. The inside of the machine is nickel-plated, and there is an arrangement whereby the cooling may be done rapidly, through a coil inside the jacket, this coil being connected to the brine circulation of the refrigerating machine.

Continuous Apparatus for the Production of Large Quantities of Soured Milk

Fig. 9—This apparatus is made by the Dairy Machinery and Construction Company of Shelton, Conn., U S A. The milk is agitated inside a jacketed cylinder, where it is allowed to incubate at about blood heat. The milk can be rapidly heated and also rapidly cooled by means of this apparatus.

The machine is filled with milk containing three per cent. of fat, which has been previously pasteurised to about 190° F., and cooled down to about 90° F.; at this point the pure culture of Bacillus bulgaricus is introduced, and the agitator is kept working, so as to mingle it thoroughly with the milk. The agitator is then stopped until the acidity shows a test of 0.9 to 1.0 per cent., when the agitator is again started, and cold brine from the refrigerating machine is turned on to the cooling pipes, so that the product is thoroughly broken up, and cooled down to 40° F.

The milk is then transferred to a bottle-filling machine (Fig. 10), poured into bottles and hermetically sealed, after which it is ready for consumption. When it has to be kept for any time it should be placed in a cold room where there is a temperature not higher than 40° F.

The process, therefore, is a simple one, and lends itself to the ordinary dairy business, without involving any great expenditure on account of a new plant.

CHAPTER V

THE BACTERIOLOGY OF FERMENTED OR SOURED MILK

A CHAPTER FOR STUDENTS

During the last few years much work has been done in investigating the action of various classes of organisms—bacteria, yeasts, and moulds—upon milk and its products. While, however, the attention of the dairyman has been chiefly directed to the propagation of acid-producing organisms and the use of pure cultures of lactic acid bacteria in their relation to butter and cheese making, a new sphere in micro-biology has been disclosed by the study of the effects caused by the combined growth of two or more different classes of organisms in milk and the consequent production of lactic, alcoholic, and gaseous fermentations. The simultaneous occurrence of these fermentative changes is responsible for the formation of such beverages as keffir, koumiss, milk-wine, etc. It has therefore become essential, in connection with the study of new developments in the milk industry, that we should make a more intimate acquaintance with the bacteriology of the ferments involved.

Keffir (kephir, kifyr, kiafyr, kephor, kyppe) is the name given to an acid, slightly alcoholic drink, which for many centuries has been prepared by the nomadic tribes in the Caucasus. The characteristic fermentation is induced by the addition of so-called keffir grains. These are yellow or golden-yellow, warty, and furrowed flakes or nodules, the former varying in size from that of a rice grain to that of a bean, while the latter are often about an inch across and one eighth of an inch thick. Bearing in mind the fact that the preparation of keffir has been carried on for many centuries, it is not surprising that the origin of these grains should be surrounded by myths.

The belief is prevalent among the Mohammedan tribes of the Caucasus that keffir grains were, in the first instance, presented by Allah, as a sign of immortality, to one preferred tribe. Others hold that, in past ages, they were found by shepherds growing on a shrub in the Caucasian highlands; while, according to Skolotowski,[47] they were originally found adhering to the walls of an oaken vessel used for the preparation of airam. This is a soured milk beverage similar to keffir, but possessing a weaker alcoholic fermentation, and prepared from goats' milk by the addition of pieces of calf's stomach. This would undoubtedly serve to introduce various species of lactic acid bacteria, and will be referred to in the portion dealing with soured milks. Keffir is prepared by the Caucasians from cows', sheep's, or goats' milk, and the operation is carried on in large leathern tubes or bottles. After the addition of the grains or seeds to the milk the vessel is placed in a cool chamber, and the fermentation is allowed to proceed for one or two days, by the end of which time the normal fermentation is at an end. During this period the keffir grains have increased enormously in size, assume a bright yellow colour, and lose their sour buttery smell.

Previous to the removal of the fermented liquid, a portion of the bottle is firmly bound from the rest by a stout cord, and the greater portion of the remaining keffir is quickly removed for use, thus avoiding, as far as practicable, any outside infection. After the addition of fresh warm milk the cord round the end of the bottle is removed, and the old and new milk thoroughly mixed for a time in order to ensure uniform inoculation of the new milk for the next fermentation. During the winter months the leathern vessels are often placed in the sunshine, so that the temperature remains at 61° to 65° F.

The necessary agitation of the vessel is said to be supplied in the form of kicks by passers-by or by the children during their play.

The beverage prepared in this way is so gaseous in character that it is often blown forcibly from the vessel during removal, and possesses, according to Podowyssozki,[48] a very acid taste.

During any interruption in the preparation of keffir in the above manner, the grains are taken out, and after having been well washed in clean water, are spread out on a clean cloth to dry in the sunshine. They thereby assume a characteristic cheesy or buttery odour and become rather darker in colour. Thorough desiccation is essential in order to prevent subsequent mouldiness or disease of the grain.

In European countries the grains are subjected to a preliminary soaking in water for five to six hours and then placed in four to five changes of milk, each change having a duration of two to three hours. As soon as the grains commence to rise to the surface of the milk, they may be used for the actual preparation. To this end, a small quantity of the grain is added to freshly boiled milk and allowed to stand for eight to twelve hours at a temperature of 55°-62° F. with agitation of the flask every two hours. By this time the milk, now known as Sakwaska, has become abundantly inoculated with the organisms essential to the fermentation, and after the removal of the grains, may be poured into well-corked flasks for the secondary brew. The flasks should be kept at a lower temperature for twenty-four to forty-eight hours, by which time the product is ready for consumption.

According to the temperature and length of period to which this subsequent fermentation is allowed to proceed, the resultant keffir is more or less acid and gaseous. The grains may again be used for starting a fresh portion of milk, and a regular supply obtained in this manner. Well-fermented forty-eight-hours-old keffir should be an effervescent beverage with prickling and acid taste and a consistency and smell similar to sour cream. Large, persistent bubbles should form on the surface of the liquid and the casein be present as an extremely fine flocculent precipitate which remains suspended for a considerable time.

From the third day there ensues a gradual peptonisation of the casein. If the temperature at which the secondary fermentation has occurred should be higher than 72° F., or if the milk has not been sufficiently agitated, then the casein will be present in the form of porous small flakes, which on shaking form a fine emulsion.

The chemical changes undergone by the milk during the preparation of keffir are confined almost exclusively to the milk sugar. As already stated, a slight peptonisation occurs in old samples, but this depends very largely upon the method of preparation and purity of the culture. Hammersten[49] and Essaulow[50] show, however, that this is not a concomitant of normal fermentation. According to Hammersten, normal keffir contains—

In no case should the acid be higher than 1.0 per cent., and the alcohol more than 0.75 per cent.

Biology of the Keffir Grain.—The first communication on the biology of the keffir grain seems to have been made by Kern.[51] He regarded the grain as a zoöglœa composed of bacilli and yeasts, the latter being regarded as the ordinary beer yeast (Saccharomyces cerevisseæ), while to the former he gave the name of Dispora caucasica. As the name indicates, this bacillus possesses two polar spores, and germination of these proceeded in the same manner as with Bac. subtilis. As, however, pure cultures of the organisms were not made, and the descriptions and illustrations made by Kern fail to show any distinctive characteristics, it seems probable that accidental confusion with other organisms must have occurred.