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

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

The size of the package also has an effect on the keeping quality; the smaller the package, the greater is the surface exposed to the air and the more rapidly the butter deteriorates. Butter used in the United States Navy is packed in hermetically sealed cans so as to exclude the air as far as possible.

From the fact that any condition which restrains or inhibits the growth of micro-organisms has a tendency to improve the keeping quality of butter, it would appear that the detrimental changes in the quality of butter are due to biological causes. The most common defect known is that usually referred to as rancidity. There are, however, different types of changes that are probably included under this head and it is very probable that different causes are operative in their production. True rancidity is probably due to biological causes; the so-called tallowy change, in which the butter acquires the odor of tallow is probably due to the combined action of light and air on the fat.

Bacterial defects in butter. There are a number of defects in butter that are positively known to be due to the growth of bacteria in the milk or cream, or in the butter itself. The lack of flavor is looked upon as a defect in the case of ripened-cream butter. It may be due to insufficient ripening of the cream, or to the lack of acid-forming bacteria that produce the desirable flavor-forming compounds. Not all acid-forming bacteria are able to produce favorable, flavor-giving compounds; hence, sour cream butter may sometimes be deficient in flavor by reason of this fact.

Putrid butter. This specific butter trouble has been observed in Denmark, where it was first studied by Jensen. Butter affected by it rapidly acquires a peculiar putrid odor that ruins it for table use. Sometimes this flavor may be developed in the cream previous to churning. It may be caused by a number of bacteria.

Turnip flavored butter. Butter sometimes acquires a flavor resembling turnips. This trouble may be due to the feeding of such roots, the aromatic substances peculiar to them being absorbed directly by the milk and thus transferred to the butter. Weigmann traced a similar flavor to certain bacteria that entered the milk from barn filth.

Cowy odor in butter. There is sometimes to be noted an odor in butter as in milk that resembles that of the cow stable. Usually this defect has been ascribed to the absorption of these odors directly by the milk. Organisms have also been described that impart to the butter a very similar odor. Bitter butter may be due to the feed that is consumed by the cow, or it may be due to those forms of bacteria that produce a bitter fermentation of the milk.

Other abnormal flavors. Among the numerous abnormal flavors that have been noted in butter is one of quite frequent appearance, the so called "fishy" flavor. It is now believed by many that this flavor is due to the presence of small amounts of iron or copper salts that have been introduced into the milk from utensils from which the protective coating of tin has been worn. If the milk or cream stored in such utensils develops any marked degree of acidity, the acid will dissolve a small amount of the iron or copper. The fishy flavor has not been found in sweet-cream butter as would be expected from the above explanation. In fresh butter a metallic taste is sometimes present. It is believed by some that on storage this flavor changes to the fishy flavor.

All utensils used for the storage of milk and cream should be kept in good condition so as to prevent the acid milk or cream from coming in contact with iron or copper.