Microorganisms play an important role in the changes that go on in the manufacture and ripening of various cheeses. Some of the changes brought about by organisms are closely related to flavor development, and the differences in such. changes in the various types of cheeses largely explain the differences in the flavors. Other changes that occur during the making of cheeses are related to losses, in the whey, of constituents of the original milk that may be important from the nutritional standpoint. They are influenced by variations in the manufacturing procedures, especially variations in the acidities developed by bacteria at different stages in the manufacture.