Fermentation occurs through cellular respiration, which is the the process in which glucose is broken down to produce Adenosine Triphosphate (ATP). Fermentation is a form of anaerobic respiration, as it is in the absence of oxygen. An example of fermentation is yeast. It performs fermentation to obtain energy by converting sugar into alcohol. This process is used to make many other types of food including cheese, bread, wine, etc. There are four types of fermentation, lactic acid fermentation, alcohol fermentation, acetic acid fermentation, and butyric acid fermentation (Aakash + Byju’s, N.D).