The action of bacteria is an important factor in the deterioration of butter. Organisms of various types are able to grow and produce conspicuous defects in both .the unsalted and salted product. The growth of bacteria and the accompanying development of defects are greatly influenced by the temperature at which butter is held. At storage temperatures, such as -23 .3°C., no growth occurs, but at temperatures as low as O°C. certain organisms are able to multiply and bring about various types of deterioration. At still higher temperatures additional organisms develop and cause a greater number of changes.

Defects suggesting extensive protein decomposition in butter have been encountered in various butter-producing countries. These include surface taint in Canada, rabbi to or a disagreeable aroma in Australia, a fetid odor in New Zealand, a putrid odor in Denmark and cheesiness and putrid (or limburger) odor in the United States.