Cheese is the casein of milk separated by rennet, which includes some of the fat and salts, but the potassium salts are removed by the rennet. There are many varieties, prepared in different ways, but the two chief classes are hard cheeses and soft cheeses, the former being pressed and salted. Cheese forms a highly nutritious food and an important article of commerce. In countries where meat is scarce and dear the peasantry consume large quantities to supply the nitrogenous element of their diet, and, weight for weight, cheese contains about twice as much protein as meat (Parkes). They use for this purpose the heavier, less highly flavoured cheeses. The wealthy classes eat cheese more as a condiment, taken after meals, and therefore they require higher flavoured varieties, which please the palate and excite the secretion of gastric juice. Eaten in moderation, such cheeses are an aid to digestion. Taken with milk, cheese tends to reduce the size of the coagulae in the stomach. Old "poor" cheese - i. e., cheese made without fat, consisting of almost pure casein - is difficult to masticate thoroughly, and is slowly dissolved in the gastric juice, hence it is slowly digested. It may act as a gastric irritant and be hurried into the intestine to excite indigestion there.

Such cheese may be rendered more digestible by cooking it after grating with bicarbonate of potassium in the proportion of a quarter of an ounce to the pound of cheese. Cheese which retains some fat is friable, light, and easy of digestion.

About 250,000,000 pounds of cheese are annually produced in the United States alone, and much so-called foreign cheese is produced in this country.

The kinds of cheese differ somewhat in composition, but in general they may be said to contain from 35 to 55 per cent of water and from 10 to 20 per cent of fats, 20 to 30 per cent of casein, and about 6 per cent of salts.

Cheese is rich in fat or in flavour according as it is made from whole or skimmed milk. Cream cheese contains about 77 per cent of fat, and the highly flavoured Roquefort, Edamer, Cheshire, and Emmenthaler, or Schweizer cheeses have a similar quantity, and are nutritive when they can be digested.

Bauer's analysis of cream cheese places the fats much lower, and the casein is also at a minimum.

Bauer's Analysts of Cream Cheese

Water.

Nitrogenous matter.

Fat.

Extractives.

Ash

Cream cheese

35.75

7.16

30.43

2.53

4.13

Whole milk

46.82

27.62

20.54

2.97

3.05

Skimmed milk

48.02

32.65

8.41

6.80

4.12

Cheese is usually prepared from sweet milk. The coagulation is accomplished in a few minutes by the addition of the ferment rennin with gentle heat (1200 F.). The heat secures firmer coagulation. Casein may also be coagulated by acids. A little salt is added; the curd is strongly pressed in a mould, and the expressed fluid is called "whey." The curd is then salted and dried on the surface by frequent turning in the air. The harder cheeses are made under higher temperature and pressure. Cheese is kept for a time to " ripen," by fermentation or decomposition. If the decomposition goes too far, it develops leucin and tyrosin. The casein may become soluble in water, producing soda albuminate and peptones. The "riper " a cheese the greater is its value as a condiment.

During the ripening volatile fatty acids are evolved from the fatty matter present, which occasion the odour and flavour. The casein also undergoes change, and is partially converted into fat (Foster). It may putrefy and evolve ammonia, or even become poisonous. Ripening, when not carried too far, makes cheese more friable, and hence more digestible.

Cream cheese is fresh, and usually not ripened, but Neuchatel is ripened.

Pot cheese is eaten fresh after the whey has been expressed. It contains: Water, 60.27 Percent I casein, 24.84 per cent; fat, 7.33 per cent; ash, 4.02 per cent; milk sugar and lactic acid, 3.54 per cent.

The quality of cheese depends upon the richness of the milk in fat. In the richest cheeses made of whole milk, such as Stilton, double Gloucester, Gorgonzola, and Roquefort, cream is added. Single Gloucester, American, and similar cheeses are made from milk from which the cream has been removed. Dutch, Suffolk, and Parmesan cheeses are also made from skimmed milk, and are "poor." Being nearly pure casein, they are hard to digest in bulk. These latter varieties keep well, and become hard enough to be grated. Fat separates the flocculi of casein and makes cheeses soft, friable, and rich, but they sooner decay.

The two soft cheeses most used in this country are Camembert and Brie.

Camembert is a cheese made of whole milk, which is very carefully dried under regulated temperature. It requires three or four weeks to ripen. This cheese, as well as the following variety, is made in St. Lawrence County, Pa., as well as in Europe.

Brie cheeses are manufactured in three grades of richness, according to whether the milk is whole, partly skimmed, or skimmed.

Roquefort is a hard cheese made in the department of Aveyron from goat's milk, partly skimmed and coagulated with rennin. The curd is then pressed for half a day, dried for ten or twelve days, and ripened in caves. This cheese is streaked with bluish lines, which are formed by the addition of a mould which grows on stale rye bread. This cheese is also made along the shores of the Great Lakes in this country, where conditions of climate, pasturage, and water favour its production.

Gruyere was originally a hard Swiss cheese, but is now made also in France and elsewhere. It is dry, aerated with large holes, and it can be crumbled. It is manufactured in three grades, according to the degree of skimming of the milk, and the curd is cooked a short time before it is pressed. It has a somewhat saltish taste.

Gorgonzola is a Piedmontese cheese made with hot and cold curds from two milkings, which do not perfectly unite, but which form minute interstices in which a green mould called "parsley " grows and imparts a high flavour (Clark). The curd is hung in hempen cloths to ferment. It is well salted.

In the United States much of the cheese manufactured is of the common sort called "American cheddar," but Neuchatel, Stilton, pineapple, and other more highly flavoured varieties are also extensively produced. "Swiss" cheese is made in Ohio and Wisconsin. An imitation cheese is also prepared from a mixture of one part lard and two or three parts milk, mixed or emulsionised at 1400 F. This emulsion is then added with buttermilk to skimmed milk, so that the finished product contains about 14 per cent of lard (Caldwell).

Toasted cheese is one of the most indigestible articles of diet, unless the cheese is new, "poor," and cut thin. " Welch rarebits " are notoriously difficult of digestion, although highly nutritious when absorbed. It is, an old saying of such cheese that it is "gold in the morning but lead at night".

Certain low organisms, moulds, fungi, etc., flourish in cheese and make it very irritant to the stomach. Such are the Aspergillus glaucus and Sporendoneum casei, both of which give a red colour, the cheese mite (Acarus domesticus) and the maggots of a fly (Piophilia casei). Bad cheese has been known to produce poisonous symptoms (see Ptomaine Poisoning) resembling those of poisoning by sausage meat.

Plasmon is an albumin food made from milk from which the fat has been removed. It is practically a dried form of casein. It is a tasteless, odourless, white, dry powder, soluble in water. It may be given every hour or two in teaspoonful doses in ten tablespoonfuls of water, or with an equal quantity of sugar an ounce of plasmon may be stirred into half a pint of boiling milk (C. Virchow). It may be added to broths and gruels, or to such starchy foods as boiled rice or mashed potatoes. This food contains over 90 per cent of pure protein in very digestible form. Plasmon biscuits and a plasmon chocolate are also manufactured.

Nutrose or casein-sodium is a form of milk casein which may be added in half-ounce doses to broths, gruels, or cocoa, in which it is soluble. It contains, according to Bruno Oppler, about 90 per cent of pure proteid. It furnishes a small volume of feces when this is desirable after operations upon the intestines.

Sanose is an albuminous food consisting of 80 per cent of powdered casein and 20 per cent of egg albumin. It is a white, odourless, tasteless powder forming an emulsion in water. It may be given in milk, cocoa, purees, or soups. From two to six tablespoonfuls may be given daily.