Fermentation is a chemical breakdown of substances in which microorganisms and enzymes (such as yeast and bacteria) convert carbohydrates into organic acids and alcohol. Fermentation occurs naturally in every animal's gastrointestinal tract and widely used for millennia as means to preserve food. Over centuries, humankind has mastered replicating the technique, and some of those processes are employed to produce kombucha and kefir.

Fermentation plays several vital roles in the human body: it breaks down hard-to-digest nutrients for the body to more efficiently absorb and convert to energy. The bacteria that facilitate this digestion are essential to our living and have co-evolved with us over thousands of years. Fermentation also helps preserve food, which was crucial for surviving long winters and surviving food scarcity without using refrigeration.

Those of us who live in urban areas have minimal exposure to bacteria due to several reasons, such as our increase in the use of chemicals and antibacterial products, decreasing interaction with nature, and the sterile nature adopted by the modern food system. Despite reducing the spread of harmful pathogens and diseases in many ways, these changes also eliminated the helpful microorganisms from our diets and lives. They inadvertently encourage other types of health problems to occur. One of the best ways to get more beneficial bugs into our bodies is by eating fermented foods. Not only can they amplify the nutritional benefit of food we intake and aid with digestion, but they also increase the number of good bacteria that live in our gut, which improves our immune system.