There were many heated debates in the nineteenth century about the relationship between chemical reactions and living organisms. Some scientists felt that fermentation was an activity of living things and, therefore, could not take place outside of living cells. This was proved by the work Louis Pasteur undertook for the French wine industry. Indeed, in the 1850s, the French wine industry was having serious trouble with wine that had spoiled. The French emperor, Napoleon III, called in Pasteur to help. Pasteur knew that the fermentation which produced wine was caused by living yeast cells. But now he found that certain bacteria could also carry out fermentation. He discovered that fermentation by bacteria spoils wine because it produces vinegar (acetic acid) instead of the alcohol produced by yeast. Pasteur suggested that the winemakers heat the wine for a short time to destroy the bacteria. They were horrified, but it worked. The process, pasteurization, is still used today, especially for milk.