The type of fermentation that occurs in yeast is alcoholic fermentation. The Dutch merchant Antoni van Leeuwenhoek was the first to observe the action of yeast under powerful lenses in the 17th century.
Alcoholic fermentation, otherwise known as ethanol fermentation, is an anaerobic process that drives the release of cellular energy by converting biological fuels, such as sugars, into ethanol and carbon dioxide. The microorganisms that carry out alcoholic fermentation are unicellular eukaryotic fungi called yeasts. Earlier scientists thought these microorganisms were nonliving. The significant role that yeasts play in fermentation only became apparent with the advent of high-quality microscopes and lenses.