Vinegar is used in various dishes, including dumpling dipping sauces, sweet and sour pork tenderloin, and pickled vegetables. Vinegar has a unique aroma; what exactly creates that strong, pungent sourness? Let's explore the brewing process of vinegar and its health benefits!

　　Vinegar can be brewed from grains like rice and barley, and fruits like apples and grapes, giving it a distinctive sour and pungent taste. The carbohydrates (starch) in grains and the sweet components (sugars called "monosaccharides") in fruits are transformed into acetic acid, the characteristic component of vinegar, by the action of microorganisms.

　　Fermentation Produces Sourness

　　Microorganisms, during their metabolic activities, transform surrounding substances into other substances; this is the fermentation process. Vinegar is brewed using this process.

　　The most common vinegar is made from grains like rice. The starch in the grain is first broken down into small sugar molecules (glucose) by Aspergillus oryzae, then further broken down into ethanol and carbon dioxide by yeast. This completes the brewing process. Adding acetic acid bacteria to the alcohol and allowing it to continue fermenting produces vinegar. Acetic acid bacteria oxidize the ethanol (the main component of alcohol), producing acetic acid, which gives vinegar its sour and pungent taste. All types of vinegar contain about 4% to 5% acetic acid.

　　There are many types of vinegar, such as apple cider vinegar and red wine vinegar. Although the secret to brewing them all involves adding acetic acid bacteria to alcohol and fermenting (acetic acid fermentation), different types of vinegar have different colors and tastes. The acetic acid itself doesn't cause these color and taste variations. For example, the unique flavor of apple cider vinegar comes from the malic acid specific to apples; the astringency of red wine vinegar comes from the polyphenols and tartaric acid in the grapes used as raw materials.

　　The Fermentation Process of Making Vinegar from Rice

　　Vinegar is made from starch in grains like rice and barley, or monosaccharides like fructose in fruits like apples and grapes. First, Aspergillus oryzae and yeast are used to ferment rice and barley into alcohol, then acetic acid bacteria are added to turn the alcohol into vinegar.

　　Absorbing Oxygen, Turning Alcohol into Vinegar

　　There are many types of acetic acid bacteria. Different types of acetic acid bacteria have different abilities to produce acetic acid and different tolerances to acid concentration, so they are used differently depending on the vinegar brewing method.

　　Acetic acid fermentation in vinegar brewing is divided into two main categories: "static fermentation" and "deep fermentation." Static fermentation involves adding acetic acid bacteria to pre-made alcohol and letting it sit for 3 weeks to 2 months. Because acetic acid bacteria fermentation requires oxygen, static fermentation only occurs in the biofilm formed on the surface of the alcohol. Vinegar brewed using this method has an acetic acid concentration of about 5%.

　　Another method is deep fermentation, where the alcohol is poured into a tank called a "fermentation tank" that provides uniform oxygenation for fermentation. This method allows the alcohol to fully contact with oxygen, resulting in vinegar with an acetic acid concentration more than 10% higher than that produced by static fermentation. Therefore, vinegar brewed by deep fermentation is often diluted for use or used commercially.