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Which substances did Louis Pasteur study while investigating fermentation?

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Painting by Albert Edelfelt showing Louis Pasteur in his laboratory, holding a glass flask and examining it intently, surrounded by scientific equipment on a workbench. — Louis Pasteur In the 19th century Louis Pasteur's work established the germ theory of disease, proving that microorganisms cause fermentation and sickness, which led to the development of pasteurization, aseptic techniques in medicine, and effective vaccines for diseases such as rabies. (Painting by Albert Edelfelt, 1885.)

While investigating the process of fermentation, Louis Pasteur conducted extensive research into several specific substances and chemical compounds. His studies included:

Alcohol: Pasteur began his research by examining problems related to alcoholic production at a local distillery.12
Lactic acid: He investigated the production of this compound, which is responsible for the souring of milk.12
Butyric acid: He conducted detailed studies on butyric acid fermentation, which led to his discovery of the Pasteur effect and the distinction between aerobic and anaerobic organisms.13

Through this work, Pasteur demonstrated that specific microorganisms are associated with each particular type of fermentation, providing the foundation for the germ theory of fermentation.12