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

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

Fig. 37.—Gassy Cheese.
Such a cheese is worthless on account of its poor flavor. The irregular holes are mechanical. The crack on the upper side is due to the pressure of the gas which has caused the cheese to bulge at this point.

The gas formed in the curd before the cheese is put to press can be gotten rid of by proper manipulation of the curd. While this treatment may improve the appearance of the cheese, it does not eliminate the substances that impart to the cheese undesirable qualities.

Gassy curds have also been treated by washing the curd with cold water. Care must be taken in applying this method for the removal of too much of the sugar and acid from the curd by the washing will permit the growth of injurious forms of bacteria. The addition of salt or of saltpeter has also been made to the milk in order to overcome gassy conditions in the milk. In the handling of gassy milk, the usual practice has been to develop a larger amount of acid before drawing the whey than in the case of good milk. This was done with the idea that acid suppressed gas formation. It has been shown previously that this is not the case. It has also been shown by Doane that the development of too much acid before drawing the whey is likely to result in undesirable flavors, producing what is known as "high-acid" or "sour" cheese.

The gas-forming bacteria grow best at high temperatures; hence, cheese kept under these conditions are more likely to be affected by this trouble than are those kept at lower temperatures.

The most successful method of preventing trouble with gassy milk in cheese making is to eliminate undesirable milk by frequent testing of the supply of the different patrons by means of the Wisconsin curd test.

Not only gas-forming bacteria may be the cause of gassy cheese, but the lactose-fermenting yeasts may cause similar trouble. If these are abundant in the milk, a considerable part of the sugar may be fermented by them, in which case, carbon dioxide gas is abundantly formed. The cheese thus rendered gassy will present the same appearance to the eye as where the gas is formed by bacteria, but will have a different flavor. The odor of alcohol may be evident, and if most of the sugar has been fermented by the yeast, the acidity of the cheese may not be sufficient for the pepsin to exert its digestive action.

Milk containing many gas-forming bacteria occurs most frequently in summer. It is claimed by some that the milk of cattle pastured on low lands is more likely to contain the gas-forming organisms than that from cattle running on higher lands. If this is true, it must be due to the bacterial content of the soil; the udders of the animals become soiled as they lie on the ground, and during the milking, the dust finds its way into the pail. Many cheese makers think that the milk from an animal suffering from a garget may be the cause of the huffing of cheese. This belief is undoubtedly well founded, as some of the bacteria known to be the cause of garget are gas-forming.

Bitter cheese. In a previous chapter the bitter fermentation of milk has been discussed. If milk containing large numbers of such organisms is made into cheese, the bitterness is very likely to be noted in it. Cheese made from milk containing few or no lactic bacteria is likely to develop a bitter taste, due to the growth of the digestive bacteria that are able to grow through the lack of acid in the cheese.

If the milk contains considerable numbers of yeasts, a sweet or fruity flavor is apt to develop, due to the products of the fermentation of the sugar by the yeast. This flavor resembles that of fermented fruit, or the bouquet of certain kinds of wine.