We have, then,
| Milk. | - | Cream. | - | Butter. | - | Water. | ||||||
| Butter-milk. | ||||||||||||
| Skimmed milk. | - | Curd. | - | Buttery and cheesy residuum. | - | Pure water. | ||||||
| Sugar of milk. | ||||||||||||
| Whey. | Salts. | |||||||||||
It may be stated, in other words, that milk is composed chiefly of caseine, or curd, which gives it its strength, and from which cheese is made; a butyraceous or oily substance, which gives it its richness; a sugar of milk, to which it owes its sweetness, and a watery substance, which makes it refreshing as a beverage; together with traces of alkaline salts, from whence are derived its flavor and medicinal properties; and that these constituents appear in proportions which vary in different specimens, according to the breed of the animal, the food, the length of time after parturition, etc.
Milk becomes sour, on standing exposed to a warm atmosphere, by the change of its sugar of milk into an acid known as lactic acid; and it is owing to this sugar, and the chemical changes to which it gives rise, that milk is susceptible of undergoing all degrees of fermentation, and of being made into a fermented and palatable but intoxicating liquor, which, by distillation, produces pure alcohol. This liquor is extensively used in some countries. The arrack of the Arabs is sometimes made from camel’s milk.
The Tartars make most of their spirituous liquors from milk; and for this purpose they prefer mare’s milk, on account of its larger percentage of sugar, which causes a greater and more active fermentation. The liquor made from it is termed milk-wine, or khoumese. It resembles beer, and has intoxicating qualities. The process of manufacture is very simple. The milk, being allowed first to turn sour, is then heated to the proper temperature, when it begins to ferment; and in a day in summer, or two or three days in winter, the process is completed, and the liquor may be kept several weeks without losing its good qualities.
The admirable though complicated organization of the udder and teats of the cow has already been explained, in speaking of the manner of milking. But it may be said, in general, that the number of stomachs or powerful digestive organs of the ruminants is wonderfully adapted to promote the largest secretions of every kind.
The udder of the cow, the more immediate and important receptacle of milk, and in which other milk-vessels terminate, is divided into two sections, and each of these sections is subdivided into two others, making four divisions, each constituting in itself, to some extent, an organ of secretion. But it is well known that, as a general thing, the lateral section, comprising the two hind teats, usually secretes larger quantities of milk than the front section, and that its development, both external and internal, is usually the greatest.
Milk is exceedingly sensitive to numerous influences, many of which are not well understood. It is probably true that the milk of each of the divisions of the udder differs to some extent from that of the others in the same animal; and it is well known that the milk of different cows, fed on the same food, has marked differences in quality and composition. But food, no doubt, has a more powerful and immediate effect than anything else, as we should naturally suppose from the fact that it goes directly to supply all the secretions of the body. Feeding exclusively on dry food, for instance, produces a thicker, more buttery and cheesy milk, though less abundant in quantity, than feeding on moist and succulent food. The former will be more nutritive than the latter.
Cows in winter will usually give a milk much richer in butter and less cheesy than in summer, for the same reason; while in summer their milk is richer in cheese and less buttery than in winter. As already intimated, the frequency of milking has its effect on the quality. Milking but once a day would give a more condensed and buttery milk than milking twice or three times. The separation of the different constituents of milk begins, undoubtedly, before it leaves the udder; and hence we find that the milk first drawn from the cow at a milking is far more watery than that drawn later, the last drawn, commonly called the strippings, being the richest of all, and containing from six to twelve times as much butter as the first.
Many other influences affect the milk of cows, both in quantity and quality, as the length of time after calving, the age and health of the cow, the season of the year, etc. Milk is whiter in color in winter than in summer, even when the feeding is precisely the same. At certain seasons the milk of the same cow is bluer than at others. This is often observable in dog-days.