Fermentation is the process that occurs when there is not enough oxygen in yeast cells for aerobic respiration. Fermentation is the process that converts sugars to acids, alcohol or gases. It is also a metabolic process. It also occurs in bacteria and muscle cells that have been starved of oxygen. Yeast cells obtain their food from simple sugars. These sugars are broken down into products that the yeast cells can use. Carbon dioxide and alcohol are by-products of fermentation.
