Most involve the genus Saccharomyces. These yeasts covert six carbon sugars such as glucose to ethanol and carbon dioxide and live under anaerobic conditions. Alcoholic beverages are known from virtually all cultures. These beverages are major social problems, but also sources of nutrition. Many plants have been used to prepare alcoholic beverages.
Plants often store nutrition as starch.
Yeasts cannot use starch. The starch is broken down by enzymes in the plant into sugars. The sugars are then converted by the yeasts into ethanol and carbon dioxide. Alcohol is a lipid and moves freely across membranes in the stomach. Alcohol is broken down in humans, but also affects the neurons and is a non-selective central nervous system depressant.