MILK FErnIENTAnoxs. Milk is subject to a great variety of fermentations. for it is a favor able medium for the growth of many kinds of bacteria, yeasts, and other fungi which cause numerous changes in its constituents. Thus, while one class of organisms curdles milk by the production of lactic acid. another class gives it an alkaline reaction. at the same time enrolling it; others impart to it a deep blue, violet. yel low. green, or red color. by the production of pigments in the milk; others give it a bitter or other unpleasant taste; another class produces alcohol from the milk sugar. and is taken advantage of ill the preparation of such bever ages as kouthiss and kephir tqq.v.), and still others cause putrefaction. The most common and familiar change is the souring of milk, due usu ally to the action of lactic-aeid bacteria. Under ordinary conditions normal milk nearly always undergoes some sort of lactic fermentation cm standing. The production of lactic acid soon curdles the milk and obscures all other forms of fermentation. and the acid stops the growth of other bacteria so that no subsequent effects arc usually seen. The popular belief that the elec trieity in the air during thunderstorms sours milk appears to be unfounded. but its rapid sour ing at such times is due to the climatic condi tions prevailing, which hasten bacteria] growth. The same diffieulty in keeping milk is experienced during very hot weather. Curdling is not al ways due to the formation of acid; milk appar ently 'sour' may have no acid taste. In such eases the cause is due to alkaline fermentation, induced by another class of organisms. The milk becomes coagulated into a soft slimy mass, II hiell is usually hitter and has an alkaline or neutral reaction. Ordinarily this form of fermentation is not very apparent, as the organisms eausing it grow slowly and I he hulk-acid organisms gel the start of them. The organnusns whieh produce lintyrie acid in milk attack and decompose the fats. giving a rancid odor. the ordinary han dling of milk the latter are of little importanee, but it is supposed that they have an important effect upon the keeping properties of butter. Several organisms have been described %Odell im part a bitter taste to milk. due. in some cases at least, to the production of a bitter principle. Milk which has been boiled is likely to develop a hitter taste, for the reason that the heating kills the lactic-acid germs, while the bacteria causing the bitter taste usually possess Louie spores which are not destroyed by heat, and so have a clear field for action. A slimy fermenta tion of milk is a somewhat common occurrence, and occasionally produces great trouble in dai ries, since it destroys the milk for all ordinary uses. Such milk becomes thick and ropy, will not cream, cannot be churned, and is unfit for drinking. It may be caused by a variety of or ganisms. There are several forms of the trouble.
One known as the 'hunge wei' (long or stringy whey) is made use of in the manufacture of Edam cheese in Holland, to control the gassy fermentation of the curd.
In addition to the fermentations and other changes in milk due to micro-organisms, rennet, an unorganized ferment obtained from the stom ach of the calf and from some plants, ferments milk, causing it to curdle. This ferment is em ployed in eheese-Making to produce the curd. Babcock and Russell have discovered an unor ganized ferment termed galactase in milk, which they believe to he a normal and inherent con stituent, and which is active in the ripening of cheese, causing the characteristic changes in the green cheese whieh make it suitable for eating.
The chief sources of bacteria in milk are the cow herself, the milker, the dust of the stable, and the dairy utensils. It has long been believed that pure milk drawn from a healthy cow con tains no bacteria, and that all bacterial contami nation of the milk comes from external sources. However. the large calibre of the milk duct makes it possible for bacteria to enter it and grow to a considerable extent, so that it becomes a matter of extreme difficulty to obtain milk from the cow, even with the greatest precautions, which shall not be contaminated. The hairs of the cow are always covered with dirt and dust, and the air of the stable is charged with dust from the fodder and bedding material, so that it is impossible to prevent some of this dirt falling into the milk pail. Thus large numbers of bacteria, especially in poorly ventilated stables, reach the milk. Any dirt upon the hands or clothing of the milker will have abundant chance to get into the milk pails and cans. The milk vessels themselves are an important source of contamination, the cor ners and creases retaining bacteria which have not been removed or killed by the washing. The warm milk fnrnishes favorable conditions for the growth of these micro-organisms which have gained access, and which for a time multiply rap idly.
Several species of bacteria classed as patho genic organisms are capable of living or even in creasing in milk. but since they do not ferment the milk or alter its appearance sufficiently to be detected by a physical examination, their presence is not readily determined. Except in very rare instances the milk becomes. contaminated after it has been drawn and in practically all these cases the cause of contamination is some form of un cleanliness, either of the stables, the water, the utensils, or the attendants. It is gratifying to know, however, that through the efforts of the United :states Department of Agriculture, the agricultural experiment stations, and the dairy men themselves, the sanitary management of dairies is being constantly improved, and through the vigilance of State appointed dairy inspectors unsanitary conditions are destroyed as soon as discovered.