Glasses of kefir, kombucha and water kefir on a table

Fermented Drinks: What You Need to Know

ByCraig Brockie Last updated

What fermented drinks are

Fermented drinks are beverages made by letting bacteria, yeasts or both change a liquid such as milk, sweet tea, sugar water or grain mash. An expert panel from the International Scientific Association for Probiotics and Prebiotics (ISAPP) defines fermented foods and beverages as foods made through “desired microbial growth and enzymatic conversions of food components” (Marco et al., 2021). The microbes eat sugars and leave behind acids, gas, flavor compounds and sometimes alcohol.

That definition covers a wide range, from kefir and kombucha to beer and wine. What they share is the process. What they do not share is what ends up in the glass, especially whether any live microbes survive.

Common fermented drinks at a glance

The “live microbes” column follows the ISAPP panel’s summary table (Marco et al., 2021). Any product can be pasteurized or filtered after fermenting, so the label matters more than the category.

DrinkMade fromFermented byLive microbes?
Milk kefirMilkLactic acid bacteria and yeasts in kefir grainsUsually yes
Drinkable yogurtMilkLactic acid bacteriaUsually yes, unless heat-treated
KombuchaSweetened teaYeasts and acetic acid bacteriaMost yes; some are heat-treated
Water kefirSugar water, often with dried fruitLactic acid bacteria, yeasts and acetic acid bacteriaYes, unless heat-treated
Fermented cereal drinks (such as boza)GrainsMixed bacteria and yeastsUsually yes
Vegetable brine drinksLiquid from fermented vegetablesLactic acid bacteriaYes, if not heated
Wine and most beersGrapes or grainYeastsNo for wine and most beers

A few notes on the main types. Milk kefir is made by fermenting milk with kefir grains, a mix of lactic acid bacteria and yeasts held together in a protein and sugar matrix (Bourrie et al., 2016). Water kefir uses a different kind of grain in sugar water and comes out fizzy and slightly sour (Lynch et al., 2021). Kombucha is sweet tea fermented with a starter culture, and its sour taste comes from acetic acid bacteria, the same group that makes vinegar (Marco et al., 2021).

Fermented is not the same as probiotic

People often use “fermented” and “probiotic” as if they mean the same thing. The ISAPP panel says they do not. A probiotic is a specific, identified strain shown in studies to provide a health benefit at a known dose. Most fermented drinks contain a mix of unidentified microbes at unknown levels, so they are fermented foods, not probiotics (Marco et al., 2021).

The panel suggests that a product claim “live and active cultures” only if it has not been processed to kill or remove its microbes. Pasteurized versions can still be called “foods made by fermentation.” For drinks sold as probiotic, see our guide to probiotic drinks.

Why fermented drinks may matter for gut health

The research on fermented drinks is real but young. Here is where it stands.

A diet high in fermented foods

The best-known study is a 17-week Stanford trial with 18 healthy adults per diet group (Wastyk et al., 2021). People on the fermented-food diet went from less than one serving a day to an average of about 6 servings, from yogurt, kefir, fermented cottage cheese, fermented vegetables, vegetable brine drinks and kombucha. Their gut microbe diversity rose steadily, and 19 of 93 inflammation-related proteins in their blood went down. The study was small, and drinks were only part of the mix.

Kefir

A 2023 systematic review found 16 randomized trials of milk kefir. Kefir may have potential for some oral, stomach and heart-related measures, but the authors said the evidence for heart-related measures was very limited, rated 12 of the studies at high risk of bias, and said better trials are needed before any recommendations. They also concluded that kefir appears safe for generally healthy people. Our article on kefir benefits goes into more detail.

Kombucha

Kombucha has even less human evidence. A 2019 systematic review screened 310 articles and found only one study reporting kombucha results in people. A 2024 controlled trial gave kombucha to 16 healthy adults for four weeks, with 8 controls, and found no significant changes in blood markers or inflammation across the group, though some gut bacteria shifted. See is kombucha good for gut health for a fuller look.

What to watch for

  • Sugar. USDA lists about 15 grams of total sugars in a 12-ounce kombucha (FoodData Central). Flavored kefirs and drinkable yogurts can carry more. The FDA Daily Value for added sugars is 50 grams a day, so check the Added Sugars line.
  • Alcohol. Fermentation can make alcohol. Under federal rules, kombucha that reaches 0.5% alcohol by volume or more at any point, including after bottling, is regulated as an alcohol beverage (TTB). Beer and wine are fermented drinks, but they are not a gut-health strategy.
  • Raw milk. Kefir made from unpasteurized milk carries the risks of raw milk. The FDA notes raw-milk outbreaks involving Listeria, Salmonella and E. coli, and says older adults, people with weak immune systems, children and pregnant women are most at risk.
  • Tyramine. The Mayo Clinic says fermented drinks such as kombucha and kefir may be higher in tyramine, which matters for anyone taking an MAOI antidepressant.
  • Weak immune systems. The National Center for Complementary and Integrative Health says the risk of harm from live microbes is greater in people with severe illness or compromised immune systems. Ask your doctor first if that applies to you.

If you brew at home

Home kombucha needs care. In 1995, the CDC reported two Iowa women who became severely ill with acidosis after drinking home-brewed kombucha; a causal link was not proven. The report advised against brewing or storing kombucha in ceramic or lead crystal containers, which can leach metals into the acidic tea.

The National Center for Home Food Preservation offers a tested kombucha recipe. It calls for sanitized equipment, a starter liquid with a pH of 4.0 or lower, and 7 to 10 days of fermenting at 68 to 77°F. Refrigerate the finished tea and use it within 30 days. It also warns that sealed bottles can build up enough gas to burst.

How to choose and use fermented drinks

Plain glass bottles of homemade kombucha in a refrigerator
  1. Look for live cultures. Words such as “live and active cultures” or “unpasteurized” suggest microbes are present. Shelf-stable drinks are more likely to be heat-treated.
  2. Buy from the refrigerated case. Most drinks with live cultures need to stay cold.
  3. Pick plain or lightly sweetened. Compare the Added Sugars line between flavors.
  4. Start small. A few ounces a day lets you see how your stomach handles it. Our guide on how to drink kefir has simple ideas.
  5. Mix it up. The Stanford diet used several fermented foods, not one drink. Our list of fermented foods for gut health offers more options.
  6. Know the downsides. Read our article on the dangers of kefir if you have a health condition.

Related topics

Sources

Craig Brockie is the founder of Ultimate Health Solutions, the company behind Ultimate Gut, and the author of Ultimate Health, The Ultimate Gut Health Guide and The Unlimited Probiotics Guide. After injuries and chronic health problems in his twenties that conventional care didn’t resolve, he began researching health on his own and has studied natural health for 30 years. He is not a medical professional, and his articles are general information, not medical advice.

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