What is fermentation and who discovered this process?

Fermentation is a metabolic process in which microorganisms, particularly yeast and certain bacteria, break down sugars in the absence of oxygen to produce energy, releasing alcohol, carbon dioxide, or organic acids as byproducts. This anaerobic process has been exploited by humans for thousands of years to produce bread, beer, wine, yogurt, cheese, and pickled foods, though the underlying science was not understood until the 19th century. Different microorganisms produce different fermentation products—yeast produces ethanol and carbon dioxide, while lactic acid bacteria produce lactic acid used in yogurt and sauerkraut production.

French scientist Louis Pasteur discovered and explained the fermentation process in the 1850s and 1860s through his groundbreaking experiments. Before Pasteur's work, fermentation was thought to be a purely chemical process, but he demonstrated that living microorganisms—specifically yeast—were responsible for converting sugar into alcohol during wine and beer production. Pasteur's research on fermentation led to the development of pasteurization, the germ theory of disease, and foundational principles of microbiology. His work transformed industries from food production to medicine and established that microorganisms play active roles in chemical transformations essential to human life.