Ethanol is prepared by fermentation of molasses. Molasses, a by product of sugar industry, has traces of sugar, which gets broken down into ethanol. The fermentation is initiated by yeast, which secretes two enzymes called invertase and zymase. These enzymes act as catalyst for converting sugar into ethanol. The reaction is exothermic and carbon dioxide is released in the process.
Yeast is mixed in the molasses.
This is undesirable. The airtight container has outlets for removal of carbon dioxide released during the fermentation process. Ethanol and water vapours that are formed are collected and separated by fractional distillation. Ethanol can also be made by fermentation of starchy materials such as barley, potatoes and maize. The starch is first converted to sugar by fermentation and then to ethanol.