The action of the yeast upon the cow's milk produces fermentations of various kinds. Among others the 18 alcoholic fermentation is worthy of note. There are also lactic ferments, and others, producing a highly desirable flavor in the beverage. In addition to this there is more or less peptonized or albuminous substances which render the beverage wholesome and palatable.

The fermentation starts rather rapidly, and in good conditions a very good fermented beverage is made in 24 hours. Much better beverages are produced, however, by fermentation which lasts three or four days, care being taken meanwhile to carefully shake the bottles every two or three hours in order that coagulation be avoided.