Fermentation
![Fermentation in progress: Bubbles of CO2 form a froth on top of the fermentation mixture.](/Images/godic/202501/18/Fermenting5230.jpg")
![Overview of ethanol fermentation. One glucose molecule breaks down into two pyruvate molecules (1). The energy from this exothermic reaction is used to bind inorganic phosphates to ATP and convert NAD+ to NADH. The two pyruvates are then broken down into two acetaldehyde molecules and give off two CO2 molecules as a waste product (2). The acetaldehyde is then reduced into ethanol using the energy and hydrogen from NADH; in this process the NADH is oxidized into NAD+ so that the cycle may repeat (3).](/Images/godic/202501/18/Ethanol_fermentation-1.svg5230.png")
![Comparison of aerobic respiration and most known fermentation types in eucaryotic cell.[6] Numbers in circles indicate counts of carbon atoms in molecules, C6 is glucose C6H12O6, C1 carbon dioxide CO2. Mitochondrial outer membrane is omitted.](/Images/godic/202501/18/Cellular_respiration5230.gif")
![Louis Pasteur in his laboratory](/Images/godic/202501/18/Portrait_of_Louis_Pasteur_in_his_laboratory_Wellcome_M00103555230.jpg")
Fermentation is a metabolic process that converts sugar to acids, gases or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation. Fermentation is also used more broadly to refer to the bulk growth of microorganisms on a growth medium, often with the goal of producing a specific chemical product. French microbiologist Louis Pasteur is often remembered for his insights into fermentation and its microbial causes. The science of fermentation is known as zymology.