The discovery of the process of fermentation dates back to 1860 when the French chemist Louis Pasteur performed a series of experiments that proved that glucose could be converted into alcohol only in the presence of fermenting bacteria and yeast.
His experiments involved measuring the multiplication of yeast and the rate of alcohol production. He found out that the fermentation rate and the reproduction of yeast were directly proportional. Alcohol was produced as long as the yeast remained alive.
Therefore, through experimentation, Louis Pasteur demonstrated that only microorganisms could ferment sugars into alcohol.
