What Is Fermentation?
In a general sense, fermentation is the conversion of a carbohydrate such as sugar into an acid or an alcohol. More specifically, it can refer to the use of yeast to change sugar into alcohol or the use of bacteria to create lactic acid in certain foods. This process occurs naturally in many different foods given the right conditions, and humans have intentionally made use of it for many thousands of years.
The earliest uses of fermentation were most likely to create alcoholic beverages such as mead, wine, and beer. These beverages may have been created as far back as 7,000 BCE in parts of the Middle East. The fermentation of foods such as milk and various vegetables probably happened sometime a few thousand years later, in both the Middle East and China. While the general principle is the same across all of these drinks and foods, the precise methods of achieving it, and the end results, differ.