Butter is made from the cream of milk by churning. It consists of about 80 per cent, of fat, 15 per cent, of water, with a little casein and sugar. A certain amount of common salt is added to increase its keeping qualities and to improve its taste. Pure cultures of certain organisms are made use of to ripen butter, and so impart a constant flavour. The rancidity which develops when butter is kept too long is due to the casein, the protein decomposing and liberating a ferment which separates fatty acids and glycerine. Butter is easily digested and absorbed. Most persons eat about an ounce a day of butter, but two or three times that amount may be taken by some people.

Margarine And Butterine

These are purified animal fats so made up as to closely resemble butter. They are made by melting down and clarifying various animal fats. The melted fat is allowed slowly to cool, and in the process the various fats solidify at different temperatures. After the stearin and palmitin have solidified, the olein is removed by pressure, churned up with a little milk, and tinted with a vegetable dye, and is then ready for use. These butter substitutes, in comparison with butter, contain fewer soluble and volatile fatty acids. The absence of butyric acid and casein is a distinct advantage, as these two ingredients are the main cause of butter becoming rancid, and therefore the substitutes "keep" much better. They have been declared to be perfectly innocuous, and are an admirable and cheap substitute for a necessary but expensive food. They could with advantage be made more use of, especially in cooking. The legal control of their sale is mainly intended to prevent them from being fraudulently offered as butter.

Cheese is another milk derivative, consisting of casein of the milk, separated by rennet, with some of the fats or oils. Cheese, as a foodstuff, presents a large amount of nutriment in small bulk, one pound of cheese containing as much nitrogenous food as two pounds of meat. In countries where meat is scarce and dear, the country people consume large quantities of the heavier, less highly flavoured cheeses. The wealthy classes eat cheese more as an extra taken after meals, and employ the higher flavoured varieties.

Method Of Preparation

In all cheese the method is to take the milk, either whole, skimmed, or fortified with cream, heat it to about 8o° F., and then curdle with rennet. The curd is then minced, strained, coloured, salted, and finally pressed into shape, the whey being thus expelled. The varieties of cheese depend upon -

(a) The quantity of water they contain; this chiefly determines the hardness or softness.

(b) The quantityof fat present,this being small in amount in cheese made from skimmed milk, and large in amount in cheese made from milk fortified with cream.

(c) The kind and degree of the fermentation processes, upon which the flavour largely depends.

The nutritive value of cheese depends largely on the proportion of fat present in its composition. There are three leading varieties - soft, hard, and skimmed milk. A fair average for the fat and nitrogen present in these three types, when fresh, is as follows (Fleischman): -

Soft.

Hard.

Skimmed Milk.

Fat

31 to 44

29

2 to 3

Nitrogen

13 to 24

28

19 to 33

Such cheeses as Stilton, Gloucester, Gorgonzola, Edam, Cheshire, and Roquefort, are examples of rich cheese made from milk fortified with cream; while skimmed milk is chiefly used in the manufacture of Single Gloucester, American, Dutch, Suffolk, and Parmesan. The fat present in the " rich cheeses " makes the cheese soft and friable, and they decompose more rapidly. This process is called "ripening".

The fatty acids present in cheese have been considered detrimental, but, on the other hand, it is possible that in some cheeses, especially the richer varieties, the acids formed by bacteria in them may be inimical to other putrefactive processes going on in the alimentary canal. If so, this would explain the absence of injurious effects from the taking of these cheeses, noted in some cases of otherwise weak digestion.

Cheese cannot be regarded as an article of diet suitable for patients with a weak digestion. This is specially true of the richer cheeses, in which the large amount of fat interferes with the ready digestion of the casein. It is well to recommend patients who are very fond of cheese to partake of one of the softer varieties, as, although less digestible, they are much less likely to be taken to excess. The addition of an alkali (e.g. bicarbonate of potash) makes it more easily digested, the alkali forming a soluble compound with the casein. This is best done by adding a pinch of the salt to 1/4 lb. of grated cheese, which may then be mixed with another foodstuff, such as milk or eggs. The large number of bacteria in ripe cheese is another factor which makes cheese an unsuitable article of diet for invalids. The recently introduced lactic St Ivel cheese is a very palatable cheese, rich in lacto-bacilli. It has undoubted advantages over other cheeses for patients not endowed with a robust digestion (see p. 544).

Buttermilk

Buttermilk is the milk left after churning, and removing the fat. Its sourness is due to the presence of lactic acid, derived from the conversion of sugar. Chemical analysis gives the following average composition: -

Water .....

91

Lactose and lactic acid . .

4.0

Casein and albumin

4.0

Fat .

•3

Ash .....

7

The casein is present in a flocculenl form, and on this account buttermilk is a readily digested food. It is a cheap food, since it is a good source of protein. A pint of it contains as much nourishment as 2 ounces of bread. It is a wholesome drink, with diuretic and special medicinal properties. These specially considered on p. 540.