Outlines of dairy bacteriology, 10th edition / A concise manual for the use of students in dairying

by H. L. Russell; E. G. Hastings

In the salting process, the salt is not mixed with the curd before it is pressed, but is applied by immersing the cheese for a few days in a saturated brine, and then rubbing salt over the surface of the cheese. In this way the salt gradually diffuses quite uniformly through the cheese. The method of salting has apparently a marked influence on the ripening process, since if the salt is added in the same way, and in amounts used in the cheddar process, the flavor will not be that of a Swiss cheese but will resemble a cheddar.

In cheddar cheese, the whey is expelled from the curd by means of the acid which is developed in the curd, and by heating the curd to a temperature of 95° F. to 100° F. In Swiss cheese the development of acid during the making process is prevented, because of the smaller number of acid-forming bacteria in the milk; other factors must therefore contribute to the expulsion of the whey to secure a firm curd. This is accomplished by cutting the curd into very small pieces and by briskly stirring it during the making, heating it during this process for a period of 20 to 30 minutes at 130° to 140° F. It might be thought that this high temperature, which is approximately that used in pasteurization would destroy the acid-forming bacteria, but these are apparently protected as they are within the curd. During the time the cheese is being pressed, the contained bacteria begin to grow and the whey coming from the cheese toward the end of the pressing shows a high acidity. If it does not show such a development of acid, the maker has reason to believe that the cheese may never ripen in a typical manner.

It has been mentioned that the milk contains but few acid-forming bacteria. The maker, however, attempts to insure the presence of a sufficient number by the use of "home-made" rennet. This is prepared by placing a piece of dried rennet, i.e., the stomach of the calf, in whey, keeping the same in a warm place for twenty-four to thirty-six hours. As the rennet contains acid-forming organisms, these grow rapidly in the warm whey, so that by adding this sour whey to the milk, the maker is not only adding rennet, that is to curdle the milk, but also a small starter of lactic bacteria. If the rennet thus prepared contains no harmful bacteria and the milk is of good quality, the cheese is likely to ripen in a normal manner. The rennet should be prepared with due regard to bacteriological principles, a condition that is rarely met in Swiss factories in this country.

Swiss cheese has two striking characteristics, the flavor and the presence of holes or "eyes." The flavor is sweetish rather than the sharp and pungent flavor of cheddar cheese. The bacteria concerned in its production are not known, but it is certain that specific organisms play some role, since if the flora of the cheese is changed by salting the curd or by the use of milk containing large numbers of lactic bacteria, the flavor will also be changed. This role of the acid-forming bacteria in Swiss is the same as in cheddar, i.e., through the acid, conditions are established for peptic action, the curd being partially digested while at the same time the curd mass is protected from putrefactive processes.

In Swiss cheese during the ripening process, holes about the size of a large cherry develop which should be quite uniformly distributed throughout the cheese. The inner surface of the hole is glistening and, in a well-ripened cheese, a small quantity of clear brine, i.e., "tears" may be noted. These holes or "eyes" may be called the trade mark of the Swiss cheese, since without them the product has a lessened commercial value, even if it possesses the typical flavor. The "eyes" are caused by bacteria that ferment the lactic acid produced by the lactic bacteria, forming from it propionic acid and carbon dioxide, the latter gas being the cause of the hole or "eye."

Fig. 38.—Swiss Cheese.
Normal development of "eyes" in a Swiss cheese. The eyes are generally as large as a cherry.

The "eye"-forming organisms cannot grow in the presence of any amount of salt, hence, if salt is added directly to the curd, the cheese is likely to be "blind" or free from holes. The eyes are formed not at the time gas holes are produced in a cheddar cheese, i.e., early in the ripening process, but after a lapse of three or four weeks. They are most abundant in the middle of the cheese since the manner of salting is such as to inhibit their formation near the surface. The eye-forming bacteria may have some effect on the flavor of the cheese.

The Swiss maker encounters the same troubles as does the cheddar maker. Gassy cheese is more prevalent in the Swiss than in the cheddar industry, since the maker cannot call to his aid the methods used by the cheddar maker, viz., the addition of a heavy starter, the washing of the curd, etc. It is especially important that the quality of the milk be first class in every respect, and yet customs prevail in the Swiss industry that are directly inimical to the production of good milk. The grossest carelessness prevails at the factories in the matter of handling the whey. It is often kept in individual barrels for each patron. (See Fig. 8.) These are not kept thoroughly clean and the result is that the whey taken back to the farm in the cans that are used to bring the fresh milk is often in an advanced stage of fermentation.

There are many other kinds of hard cheese; but in each, so far as is known, the role of the acid-forming bacteria is identical with that noted in cheddar and Swiss cheese, viz, in preparing conditions favorable for peptic action, and preventing the development of putrefactive bacteria present in the curd.