Before yeast’s metabolic processes were properly understood, the word fermentation was also used to describe a much wider range of chemical changes that resulted in the appearance of boiling and in some of which carbon dioxide evolved. These have included the leavening of bread, the production of cheese, and the tumultuous reactions of acids with alkalis. Today such changes involving the intervention of yeast or bacteria in aerobic processes are not usually considered true fermentations.
By the middle of the 19th century, our understanding of science was such that opinions were divided about the nature of ‘organized ferments’ as opposed to ‘unorganized ferments’ in fermentation. Thanks to Louis pasteur, we now know that it is the organized ferments and their agents yeasts and bacteria that are primarily responsible for alcoholic fermentation. They act through their internal enzymes (enzymes were responsible for Pasteur’s unorganized ferments), which, functioning as catalysts, mediate the series of reactions involved in the conversion of sugar into alcohol and carbon dioxide.
