Fermented foods can be categorized by type, including beverages like kombucha, beer, and mead; dairy products such as cheese, kefir, and yogurt; and vegetable-based consumables like kimchi, sauerkraut, and natto. The fermentation process differs depending on the type, but generally involves the oxidation of organic compounds. When food is fermented, bacteria produce byproducts like lactic acid that change texture and flavor in different ways. Consuming fermented foods presents both health risks and benefits.
Beverages are some of the earliest types of fermented foods produced by humans. Wine, beer, and mead are all fermented drinks. Yeast converts glucose to alcohol and carbon dioxide. Beer is made from barley, hops, and yeast. Cider is fermented apple juice, wine is made from grapes and other fruits, and mead is honey-based.
Kombucha is fermented tea that can be flavored with fruit juices and made at home or purchased commercially. A mass of bacteria and yeast called the mushroom, or SCOBY (symbiotic culture of bacteria and yeasts), forms the kombucha culture. Sugar is added to the tea, and the SCOBY feeds on it, producing a variety of acids.
Fermented dairy products are also called cultured dairy or milk foods and include products fermented with lactic acid bacteria. Cheese is a solid fermented milk product fermented with a variety of molds and bacteria, depending on the type. Yogurt is a bacterial fermentation of milk that produces a lactic acid that creates the characteristic texture. Kefir, made with kefir grains, is often made with mammalian and soy milk, but can also be made from fruit juices.
Kimchi, sauerkraut, and pickles are widely consumed fermented vegetables. Kimchi is a Korean condiment or side dish of fermented cabbage and seasonings that vary regionally. Sauerkraut is shredded cabbage fermented by lactic acid bacteria that gives it a sour taste. Natto, or soybeans fermented with hay or grass bacillus, is a breakfast food traditionally consumed with rice in Japan. Pickled cucumbers as well as other pickled vegetables are typically pickled in vinegar or brine and then fermented by lacto-fermentation.
Fish and meat can also be fermented. Fermented ground shrimp is a common Southeast Asian ingredient, as is fish sauce, a fermented sauce derived from fish. Some cured meat products, including pepperoni, involve fermentation because the process reduces moisture and impedes the growth of bacteria that can spoil the meat.
Consuming fermented foods is believed to provide some important health benefits, though some claims have not been well studied. The principal benefit associated with most fermented foods is improved digestion because these products contain acidophilus bacteria. Increasing this intestinal flora is linked to a more resilient immune system. Fermentation also biologically enriches food by increasing protein, vitamins, and essential fatty and amino acids.
There are some risks to consuming fermented foods, including the possibility of contracting botulism. Although rare, contaminated home-canned and -fermented foods can cause botulism. Proper preparation methods and fermenting at a cold temperature below 37 degrees Fahrenheit (2.77 degrees Celsius) will discourage botulism bacteria growth. High temperatures destroy the botulism toxin, so if there is doubt about the safety of a fermented food product, boiling for approximately 10 minutes can help ensure safety.