For the growth of molds and aerobic bacteria, holes must be punched in the cheese to allow oxygen from the air to penetrate.

In the early stages of ripening Emmenthal and Swiss cheeses are soft and become elastic. It is during this stage that the holes or "eyes" are formed from production of gas, principally carbon dioxide, if ripening is normal, but with more hydrogen in abnormal or early ripening. If the cheese becomes too firm before the formation of holes is complete, checks and cracks appear in the cheese.

Cheddar cheese in cans. The Bureau of Animal Industry (Rogers) has announced a practical method of canning unripened Cheddar cheese. By this method a one-way or check valve, which holds perfectly against external pressure but with internal pressure allows gases formed during ripening of the cheese to escape, is inserted in the lid of the can. Cheddar cheese has always been pressed in cylindrical forms of varying sizes, but in general rather large. When these large cheeses are cut they lose moisture, so the cut surface dries rapidly. In addition, if the cheese is well ripened, loss occurs through crumbling.

In packing cheese in cans, the cheese, after pressing, is cut into the desired shape. Since hydrogen sulfide is often liberated during ripening of cheese, it is preferable to wrap the cheese in parchment and it is necessary to use a lacquered can, for the hydrogen sulfide tends to form a black product with metals such as iron, copper, or lead.

Processed cheese. Rogers states that before the development of the can in which Cheddar cheese may be ripened, the "only commercial method for putting Cheddar cheese into a more attractive and convenient form is the one known as processing. After the rind is removed, the cheese is ground, a small quantity of water and an emulsifier, usually sodium citrate, are added, and the mass is heated with constant stirring until it becomes fluid. The emulsion is run into forms, which in many cases are boxes lined with tinfoil, in "which it is sold. The cheese hardens quickly and, as the wrapping adheres closely, there is no trouble from molds. Moreover, as the temperature is high enough to constitute pasteurization, most of the bacteria are killed and the enzymes destroyed, so that ripening is stopped. In this process, much of the original character of the cheese is lost; but, in spite of this objection, the advantage of the package is so great that a large part, possibly one-third, of all the cheese made in the United States is sold in this form."

Templeton and Sommer have investigated various salts that may be used as emulsifiers in processed cheese. They state the purpose of the salt is to prevent separation of the fat from the cheese and at the same time give the finished product the desired body and texture. They quote Habicht as stating that an alkaline monovalent cation combined with a polyvalent anion, such as sodium citrate, is the ideal emulsifying salt. The physico-chemical explanation is as follows: There is partial saponification between the cation (sodium, if sodium citrate is used) and the fatty acids. The soaps formed are good emulsifiers. In addition the anion, which is a solvent for casein, combines with the casein of cheese so that a film of casein surrounds each fat globule, thus emulsifying it and preventing its escape from the mass. Later we find that the citrate ion is also a good peptizer of egg and flour proteins.

Loaf cheese. Rogers states that blending is used extensively for Cheddar and Swiss cheese. In this process the cheese is ground and heated in steam-jacketed kettles, 60° to 70°, and then poured into molds. In the initial heating separation of the fat occurs; but with longer heating the casein becomes plastic and stringy and encloses the fat. Further agitation causes the mass to lose its plasticity and become the consistency of heavy cream. At this time it is poured into the molds.

The plasticity of the cheese is an important part of the process. Once the plasticity is broken it is almost impossible to restore it. The method of manufacture, the degree of ripening, the acidity of the cheese, and possibly other factors influence the degree of plasticity attainable in the heated cheese and the length of time the mass will remain plastic. Sodium and ammonia seem important in the emulsification of the product.

Cheese spreads. The term cheese spread may be applied to any packaged form of cheese that can be easily spread with a knife at ordinary room temperature. Templeton and Sommer name the types on the market as: (1) cream cheese, mixed with pickles, olives, etc., (2) processed cheese of such age and moisture content as to be "spready," and (3) processed cheese with concentrated whey or skim milk powder added and of such fat and moisture content that the mix will spread easily. They say that, since the composition is quite different from cheese, as defined for Food and Drug regulations, the product cannot be sold as cheese. Actually they are sold as food products under proprietary trade names. The desirable spreading qualities may be due to the moisture content or the fat content or both.

The use of cheese in cooked products. All of the factors that affect the plasticity of the cheese when heated for blending, i.e., the degree of ripening, the acidity, and method of manufacture, also affect its blending properties with other ingredients in such dishes as rarebit, cheese souffle, and macaroni and cheese. To these factors may be added the extent of drying. For the cut or grated surface of cheese may dry rather extensively. Hence, the protein in the surface area really needs soaking for hydration before it will blend with other ingredients, or it may entirely lose its plasticity.

Cream cheese may be combined with eggs, sugar, etc., for cheese cake or similar cooked dishes. But, in general, whether in its original state after curing, or processed, the Cheddar type is the cheese usually combined with cooked products.

The cheese is combined with white sauce or eggs at low temperatures and by stirring. The temperature should be as low or lower than that used for blending, 40° to 50°C. often being preferable to 60° to 70°C. As the protein becomes plastic the fat exudes. Stirring aids in emulsifying this fat with white sauce and casein of the cheese.

Cheese souffle. A colleague, Plagge, suggested a good method of combining the ingredients for cheese souffle. The beaten egg yolks were added to the white sauce before the grated cheese, because the addition of the egg yolks cooled the mixture to a greater extent before the cheese was added. However, another advantage of this order of mixing is that the egg yolk aids in emulsifying the fat of the cheese. For the same reason beating with a rotary egg beater as the cheese softens is a good method of blending the cheese with the white sauce, since it more efficiently divides the cheese, thus increasing the surface area for emulsification.

Processed cheese usually combines particularly well with white sauce and egg yolk, because of its added water content and the emulsification of the fat.