Fermentation is a type of anaerobic respiration that converts a carbohydrate into an alcohol or acid. Certain organisms use fermentation to obtain the energy they need to perform their daily activities. Most, however, obtain the energy they need through aerobic respiration. There are two basic types of fermentation. One of these is ethanol (or alcohol) fermentation. Yeast and certain bacteria perform this. It consists of breaking down pyruvate into ethanol and CO2. Ethanol fermentation is used to produce beer, bread, and wine. The other type of fermentation is lactic acid fermentation. In this process, pyruvate molecules leftover from glycolysis are broken down into lactic acid. Lactic acid fermentation occurs in animal muscles when energy is required and not enough oxygen is supplied. It is also useful in the production of yogurt.