fermentation

Black grapes on the vine at Chateauneuf-du-Papes, France. During the pressing process the yeast on the skin of the grape converts the sugar content of the grape juice into ethanol (ethyl alcohol).

Breakdown of sugars by bacteria and yeasts using a method of respiration without oxygen (anaerobic). The enzymes in yeast break down glucose to give two products: ethanol (alcohol) and carbon dioxide. Fermentation processes have long been utilized in baking bread, making beer and wine, and producing cheese, yogurt, soy sauce, and many other foodstuffs.

In bread baking, the bubbles of carbon dioxide trapped in the dough make the bread rise. In the brewing process, complex sugars, such as sucrose, are first broken down by yeast into simple sugars, such as glucose. Glucose is then further decomposed into ethanol and carbon dioxide. The ethanol produced is the alcohol in alcoholic drinks, such as beer and wine; the carbon dioxide puts bubbles into beers and champagne.

The word equation for fermentation is: glucose → ethanol + carbon dioxide. The symbol equation is:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Many antibiotics are produced by fermentation; it is one of the processes that can cause food spoilage.