Louis Pasteur a French chemist, supported the idea that fermentation was a biological process. Justus von Liebig, a German chemist, supported the idea that fermentation was a mechanical process. Both chemists had different methods of experimentation, and they focused on different aspects of fermentation because they had different ideas about where the fermentation began in an organism.
The Liebig–Pasteur feud started in 1857 when Pasteur said that fermentation can occur in the absence of oxygen. The two were aware of the other's works, but continued working with their own theories. The two mention each other, as well as other scientists, in articles and other publications about the processes and causes of fermentation.