Fermentation happens when microbes—like bacteria and yeast—break down food components, creating new flavors and beneficial compounds. Unlike the strict biochemical definition, food fermentation can happen with or without oxygen.

The microbes involved, called fermentation-associated microbes (FAM), vary depending on the food and fermentation method. Some foods, like sauerkraut, rely on the use of spontaneous microbial communities (wild microbes), while others, like yogurt, use an established community (specific starter cultures) to control the process.

It is important to note that although a fermented food may contain live microorganisms, they do not necessarily meet the definition of probiotics. Probiotics are specific live microbes that must be shown to provide health benefits. In some fermented foods, like yogurt, probiotic strains are part of the starter culture and drive fermentation. In others, such as kombucha, probiotics may be added after fermentation. The presence of probiotics does not mean a food is fermented. 

Fermentation produces compounds called metabolites that affect a food’s taste, texture, and nutrition. Primary metabolites, like lactic acid and alcohol, can help preserve food, drive the flavor profile, and can help promote health benefits, while secondary metabolites, like terpenoids, add unique flavors.

Fermented foods may also contain postbiotics—non-living microbial components or metabolites that can support health.

Understanding the science behind fermentation can help you choose foods that offer real benefits, rather than just marketing hype. Whether naturally fermented or made with a starter culture, these foods play an important role in our diets.