In biochemistry, fermentation theory refers to the historical study of models of natural fermentation processes, especially alcoholic and lactic acid fermentation. Notable contributors to the theory include Justus Von Liebig and Louis Pasteur, the latter of whom developed a purely microbial basis for the fermentation process based on his experiments. Pasteurs work on fermentation later led to his development of the germ theory of disease, which put the concept of spontaneous generation to rest. Although the fermentation process had been used extensively throughout history prior to the origin of Pasteurs prevailing theories, the underlying biological and chemical processes were not fully understood. In the contemporary, fermentation is used in the production of various alcoholic beverages, foodstuffs, and medications.