Definition. The Food and Drug Administration defines cheese, in the regulatory announcements, as "a product made from curd obtained from the whole, partly skimmed, or skimmed milk of cows, or from milk of other animals with or without added cream, by coagulating with rennet, lactic acid, or other suitable enzyme or acid, and with or without further treatment of the separated curd by heat or pressure, or by means of ripening ferments, special molds, or seasoning."

Classification of cheese. Cheese may be classified in many ways as (1) method by which the curd is produced, i.e., acid or rennet coagulation, (2) source of the milk, from cow, sheep, or goat, and (3) the texture and consistency of the cheese, i.e., whether soft, semi-hard, or hard. Many other classifications might be used but none of them are entirely satisfactory.

Doane and Lawson list and describe nearly 300 cheeses. They state there are probably about 18 distinct varieties of cheese.

For purposes of discussion, Rogers classifies cheese as follows:


Unripened Cottage Cream Neufchatel Ripened

Ripened by molds


Brie Ripened by bacteria





Ripened by molds



Stilton Ripened by bacteria


Munster Very hard

Without gas holes



Gouda With gas holes




Composition of cheese. From the standpoint of quantity the principal constituents of cheese are casein, fat, and water. In addition it contains various salts, and unless heated to pasteurization temperatures various organisms such as bacteria and molds. Different types of soft cheese may contain from 40 to 75 per cent of water, hence this type does not keep long. Hard-type cheeses usually average 30 to 40 per cent moisture. The soft types may contain from 13 to 21 per cent of protein and from 0.5 to 50 per cent of fat. Hard types contain from 20 to 45 per cent protein and 19 to 40 per cent fat.

Coagulation of milk for cheese. Coagulation may be brought about by rennet or acid. Rennet-formed curds are more elastic, the acid ones more sticky. In acid-formed curds more of the calcium salts are split off from casein, forming calcium chloride which is soluble in the whey. Rennet-coagulated cheeses of cheddar types retain about 80 per cent of the calcium of milk, whereas soft cheeses retain about 20 per cent.

The temperature for coagulation varies with the type of cheese desired. In general, the lower the temperature the softer the curd. Curds formed at 21° to 25°C. are used for some soft cheeses. Cheddar cheese has a firmer curd and the milk is brought to 30°C. before the starter and rennet are added. Temperatures as high as 48°C. may be used for some cheese, the curd produced being distinctly tough and somewhat rubbery and elastic.

Making cheese. The essential steps in making cheese are: blending the particular type of milk desired; bringing the milk to a definite temperature; adding lactic acid culture for types of cheese that need greater hydrogen-ion concentration when the rennet is added (acid cultures are added to cheddar types, but not to Swiss); adding vegetable color, if cheese is to be yellow, omitting if cheese is to be American white; and adding the rennet. After coagulation the curds are cut to the definite size for the type of cheese desired. Small curds retain less moisture within the curd but the whey does not drain so well from the curd. The next step is stirring the curd gently to facilitate draining of the whey. The curd is then ditched, salted, put in molds lined with cloth, and pressed into defi-nite shapes as Longhorms, Prints, Daisies, Flats, Twins, and Cheddars. After being pressed the cheese may be soaked in salt brine or dry salt may be rubbed on the surface. Sometimes no additional salting occurs. Soft unripened cheese is not cured; but after being pressed or molded other types are placed on shelves in caves or specially constructed curing rooms to ripen. In the latter ventilation, humidity, and temperature may be carefully controlled according to the type of cheese. The curing period varies for different types of cheese and for the same type. For example, Cheddar may be cured from 2 or 3 months to 2 years. With longer curing a sharper, richer, and fuller flavor is developed.

Cheese, after being cured, is often blended for uniform flavor, texture, and body.

Secondary heating of the curd. A secondary heating of the curd is necessary with most hard and semi-hard cheeses. Making Emmenthal involves heating to about 55° to 58°C. This heating hastens the driving of the whey from the curd, changes its texture, and often alters the bacterial flora. The heating at high temperatures decreases the moisture content and rennet action is checked if not wholly stopped. Various physical changes take place during this period, the curd becoming tough, firmer, and rubbery. In Swiss and Parmesan cheese it also acquires plasticity.

Ripening of cheese. In the process of ripening chemical and physical changes occur in the cheese. It loses its tough, rubbery qualities and becomes soft and mellow, sometimes almost crumbly. During this change as much as 50 per cent of the nitrogenous constituents may be converted to soluble forms, though the average for hard cheese is 30 per cent. These changes not only alter the texture and flavor, but also alter the cooking quality of the cheese, the increased solubility of the proteins increasing the ease with which the cheese may be blended with eggs, milk, and white sauce.

Ripening is slower at lower temperatures and more rapid at higher ones. Not only enzymes of the milk, if the milk has not been heated to a temperature to destroy the enzymes, but bacteria aid in ripening of the cheese and hydrolysis of the proteins. Some bacteria, such as lactic acid, produce enzymes that split the protein. More hydrolysis occurs in the softer center of hard cheese than near the rind. Salting affects the rate of ripening by delaying bacterial growth, the proteins of cheese with more salt becoming soluble at a slower rate. Salt penetrates slowly from the rind to the center and aids in drying the cheese. Changes in the fat in the interior of most cheese are usually negligible.