Which French chemist and microbiologist is credited with establishing the connection between yeast and fermentation?

• A. Antoine Lavoisier
• B. Cagniard de la Tour
• C. Louis Pasteur
• D. Jean-Antoine Chaptal

Answer: (C)

Understanding that fermentation is driven by living organisms, not just a purely chemical process, is what this item tests. Louis Pasteur showed decisively that yeast is the agent carrying out fermentation, converting sugars into alcohol, and that fermentation relies on living microorganisms rather than being an innate chemical reaction of the sugars. His famous experiments with sterilized broths and swan-neck flasks demonstrated that when the broth was protected from microbes, fermentation did not occur, but when yeast was present, fermentation began. This work also helped separate the biological role of microorganisms from other factors and laid groundwork for the germ theory of fermentation. While other French scientists contributed to fermentation science in varying ways, Pasteur is the one who established the direct link between yeast and the fermentation process.