The Carbohydrate Fermentation test uses Phenol Red Broth to test for the fermentation of different sugars. It is one of the fermentation tests, others include the Methyl Red test and the Voges-Proskauer test. Phenol Red Broth is a general purpose fermentation media that includes the pH indicator Phenol Red and a series of tubes each with a different sugar. Different people use different sugars, but glucose, sucrose, lactose, and mannitol are often studied. One inoculates bacteria into each tube, if the strain of bacteria ferments that sugar, an acid will build up, changing the color of Phenol Red. Sugars such as glucose undergo "fermentation" when it acts as an electron donor, such as in glycolysis, and one of its metabolic products (such as pyruvate) act as an electron acceptor in a fermentation reaction. In reality, most sugars other than glucose are said to undergo "fermentation" when it is either hydrolyzed into glucose or converted into glucose or both and then the glucose is fermented. Fermentation reactions often begin with glycolysis, but this is not always the case, especially with prokaryotes. The second step in the process is the fermentation reaction that generates end products such as different acids, ethanol, hydrogen gas, carbon dioxide gas, and other organic compounds, depending on the specific reactions. Which reactions will occur depends on the species of bacteria.