Vinegar is a kitchen pillar that is so ubiquitous and familiar that many people don’t think of it as a product of fermentation. In fact, vinegar is made by the fermentation of alcohol into acetic acid by a large family of obligate aerobic bacteria (bacteria that need air to function). These acetic acid bacteria (AAB) encompass a wide array of species. They are omnipresent and airborne and found on surfaces of most living things, including you.

As with kombucha, vinegar is a product of the collaboration between yeast and bacteria. First, yeast converts sugar to alcohol, then AAB convert the alcohol to acetic acid. The difference is that vinegar-makers will often select yeasts with a certain maximum threshold for alcohol, meaning the yeast will die off before it’s had the chance to consume all the sugars in the base liquid. (Alternatively, they will sometimes heat the alcohol to kill the yeast.) Otherwise, many yeasts aren’t adapted to survive acetic acid and will end up dying once the AAB takes over. Thus, whereas kombucha will continually grow more and more acidic until all available sugar has been converted to alcohol (and subsequently acid), vinegar will plateau at a certain acidity.  

Varieties of vinegars around the world are as diverse as the cultures that produce them, often reflecting the alcoholic spirits native to the region. East to West, we can find vinegars fermented from rice, sorghum, millet, barley, kiwi, apple, honey, berries, coconut, and beyond. The fermentable sugars in most of these products are readily available, allowing yeast to get to work straightaway. With grains like rice and barley, enzymes must first break down the starch in the grain into fermentable sugars.  

Until midway through the eighteenth century, the prevailing wisdom was that everything on earth was composed from four basic elements: fire, water, earth, and air. Antoine Lavoisier, one of the founders of modern chemistry, was the first person to suggest that air was not a pure, immutable substance, but rather a combination of components, including oxygen (a term he coined from the Greek words for “acid former”). Through rigorous experimentation using nonmetals such as sulfur and phosphorous, he correctly deduced that oxygen was being removed from the surrounding air when the elements were burned. The products of those reactions were acids. By extrapolating these results, Lavoisier came to the conclusion that the transformation of wine into vinegar occurred because of oxygen in the air, through the process of “oxidation” as carried out by AAB.  

This cognitive leap spread across Europe and led to advancements in vinegar production that exploited the idea of oxidation. Vinegar-makers were able to speed up the process by increasing the surface area of wine. German vinegar- makers developed “the quick process” to drip wine through loosely packed wood chips while simultaneously blowing the liquid with fresh air. Hundreds of years later, artisans still employ the method.

Images 2, 3 courtesy of Evan Sung