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What Is Food Fermentation?

Medically Reviewed by Dan Brennan, MD on October 25, 2021

Food fermentation is the process of creating food or changing the properties of food using microbes.

Many cultures started fermenting foods to preserve them. For example, fermenting vegetables allowed people living in places with harsh winters to eat them year-round. Cheese is another fermented food that lasts much longer than its previous form, milk. For some foods, like olives, fermentation makes an inedible or bad-tasting food edible or more palatable.

Examples of Fermented Foods

You may not know that some foods you eat often are actually. In general, it takes only a few ingredients to make some fermented foods at home, so they’re easy to add to your diet.

Fermented foods include:

  • Cheese
  • Olives
  • Yogurt 
  • Tempeh
  • Miso
  • Kimchi
  • Sauerkraut
  • Bread (if made with yeast)
  • Buttermilk 
  • Kefir 
  • Kombucha 
  • Cider 
  • Wine 
  • Beer 
  • Pickles 
  • Sour cream 
  • Vinegar 

How Are Foods Fermented?

Wild fermentation. In this process, also called spontaneous fermentation, the microorganisms that cause fermentation are already in the environment. For example, the microorganisms that make a sourdough starter — one of the ingredients in sourdough bread — come from the flour used to make it and often from the baker's hands.

Culture fermentation. This process uses a starter, like a sourdough starter, to ferment foods. Kombucha is another food that uses a starter -- in this case, a symbiotic culture of bacteria and yeast (SCOBY).

Are Fermented Foods Good For You?

Research suggests that there are some health benefits to eating fermented foods. They may help the balance of helpful bacteria that live in your intestines and help you digest food. These microbes also help your immune system fight off harmful bacteria.

Fermented foods may be especially good after you've taken antibiotics. They can help restore the balance of good bacteria in your digestive system.

Some experts believe that an unbalanced microbiome leads to leaky gut syndrome, a condition in which your intestines leak nutrients into your bloodstream. It may contribute to a range of conditions including eczema and Alzheimer's disease. Balancing your gut biome with fermented foods may help strengthen the walls of your intestines.

When choosing fermented foods, keep in mind that those with live cultures are the most helpful for your gut biome. For example, there aren’t usually live organisms in finished cheese, but there are in yogurt. Other examples of foods containing live cultures include:

  • Kimchi
  • Kefir
  • Certain kinds of pickles

In addition to helping your gut biome, fermented foods can lower your risk of heart disease. They also may help  reduce several key factors in heart disease like high blood pressure and obesity. They might lower your risk of diabetes and can help with inflammation. Preliminary studies also suggest that people who eat fermented foods may have lower "bad" LDL cholesterol levels.

Risks of Fermented Foods

If they have been prepared and handled properly, there are no documented risks to eating fermented foods. But if they’re contaminated during or after the fermentation process, there is a risk of food poisoning.

There are some risks specific to drinking too much kombucha. Health experts recommend drinking no more than 12 ounces of the fermented tea per day. Symptoms of drinking too much kombucha include:

Another risk of kombucha is vinegar nematodes. These small worm-like creatures are not harmful if consumed but can make drinking kombucha unpleasant. If you have vinegar nematodes in your home-brewed kombucha, experts recommend throwing out the whole thing, including the SCOBY, and starting over from scratch.  

Show Sources

SOURCES: 

American Society for Microbiology: "The Sourdough Microbiome."

Association of Food and Drug Officials: "Potential Hazards Associated with Fermented Foods."

Australian Academy of Science: "The chemistry of wine: Part 2 Fermentation."

Center for Global Education: "The Science of Pickling and Fermentations."

Cleveland Clinic: "5 Reasons to Add More Fermented Foods to Your Diet."

Frias, F, Martinez-Villaluenga, C, Peñas, E. Fermented Foods in Health and Disease Prevention, Academic Press, 2017.

Harvard Women's Health Watch: "Fermented foods can add depth to your diet"

Heart Foundation: "Fermented foods: the latest trend."

Institute of Food Technologists: "How Beer Is Processed."

International Scientific Association for Probiotics and Prebiotics: "Fermented Foods."

Kombucha Brewers International: "Kombucha FAQ."

Mayo Clinic: "What is kombucha tea? Does it have any health benefits?"

Microbiology, Boundless.

Nutrients: "Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease."

Schaecter, M. Encyclopedia of Microbiology, Academic Press, 2009.

Science and Technology of Fruit Wine Production: "Technical Guide for Fruit Wine Production."

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