This is a metabolic process that converts sugar to gases, acids, or alcohol using bacteria or yeast. Fermentation is known as the absence of the electron transport chain and it takes a reduced carbon source to produce products like acetate or lactic acid. There are two types of fermentation. There is lactic acid fermentation and there is alcoholic fermentation. Lactic acid fermentation is an anaerobic fermentation reaction where sucrose, fructose, and glucose are converted into cellular energy and lactate. This process occurs in animal cells and in some bacteria. Alcoholic fermentation is another process where sugars like sucrose, fructose, and glucose are converted into cellular energy and produce metabolic waste products known as carbon dioxide and ethanol. Cheese and yogurt are made through the lactic acid fermentation of milk with harmless bacteria.