Kombucha

• 1. Introduction

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  Kombucha is a fizzy, sweetened black tea that is soured on purpose by a jar of living microbes. In 2016, PepsiCo bought a kombucha maker called KeVita for approximately $200 million. That is a large sum for a drink that many people still brew in a kitchen. Floating in each homemade jar is a thick, rubbery layer that brewers call a mother. Where did this drink come from, and why are so many stories about its past untrue? What exactly is alive in the jar? And do the health promises attached to it hold up?

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• 2. Inside the Jar

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  Saccharomyces cerevisiae is the yeast most often found in a kombucha culture, but it never works alone. The whole community goes by the acronym SCOBY, which stands for symbiotic culture of bacteria and yeast. Its formal Latin name is Medusomyces gisevii. People also call it the tea mushroom, the tea fungus, or the Manchurian mushroom. Those labels mislead. The culture is a growth of acetic acid bacteria and sugar-loving yeasts held together in a gelatinous mat. Reports list many yeast genera in these cultures, among them Zygosaccharomyces, Brettanomyces, Pichia, and Candida.

  Komagataeibacter xylinus, formerly named Gluconacetobacter xylinus, is the bacterium that is almost always present. It takes the alcohol the yeasts make and turns it into acetic acid and other acids. That raises the acidity and keeps the ethanol level low. The same bacterium also produces bacterial cellulose, which is reportedly responsible for most or all of the mother's physical structure. Brewers may have favored firmer, denser cultures over time. These bacteria need oxygen, so they gather at the surface where the tea meets the air. After about 2 days they begin laying down cellulose. Acetobacteraceae make up 88 percent of the bacterial community in the SCOBY. The populations that produce acetic acid grow for the first 4 days and then decline. Bacterial diversity in the tea peaks on the 7th day of fermentation.

  Sugar is the fuel for all of this. Sucrose is broken down into fructose and glucose, and those are converted into gluconic acid and acetic acid. The finished drink also holds enzymes, amino acids, polyphenols, glucuronic acid, glycerol, and lactic acid. Its pH is typically about 3.5. By makeup it is 95 percent water and 4 percent carbohydrates, with B vitamins including thiamin, riboflavin, niacin, and vitamin B6. A small amount of caffeine comes along from the tea.

  The alcohol level is usually below 0.5 percent, but it climbs with longer fermentation. Tests of commercial bottles have found everything from undetectable alcohol to 4 percent. Left too long, the acids build until the drink tastes close to vinegar. Those alcohol readings would later cause trouble on store shelves.

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• 3. Brewing at Home

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  The recipe starts with non-chlorinated water brought to a boil, with sugar dissolved in it. Tea leaves steep in the hot sweet water and are then thrown out. Once the tea cools, the SCOBY goes in. The mixture is poured into a sterilized container along with some previously fermented kombucha, which lowers the pH. Brewers call this step backslopping. A paper towel or breathable fabric covers the top to keep out insects such as fruit flies.

  Fermentation takes up to 10 to 14 days at room temperature, between 18 and 26 degrees Celsius. During that time a new daughter SCOBY forms on the surface and grows to the full diameter of the container. When the tea is ready, the SCOBY comes out and is stored with a little of the fresh kombucha. The rest is strained and bottled for a secondary ferment of a few days, or kept cold at 4 degrees Celsius. Many brewers add juice, spices, fruit, or other flavorings at this stage.

  Some commercial producers go further and sell what they call hard kombucha, with an alcohol level above 5 percent.

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• 4. Murky Origins

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  The Bohai Sea region of China is one proposed birthplace for kombucha, though Chinese researchers do not share that view. The drink is regionally traditional in China. Before the 20th century, some practitioners of traditional Chinese medicine used it as a remedy for lung and stomach ailments, yet it was never widely known across the country.

  By the early 20th century kombucha had spread to Russia, then on to other parts of Eastern Europe and to Germany. A European work from 1852 already mentions it.

  Western marketing has spread colorful myths about the drink's past. There is no evidence that kombucha began in Qin dynasty China or that it was served to Emperor Qin Shi Huang. Nor is there evidence that it existed in Korea or Japan before the late 20th century. A tale of a Korean doctor named Kombu serving it to the Japanese Emperor Ingyo is therefore entirely apocryphal.

  Japan received kombucha from Russia. It became a health fad there after Sumako Nakamitsu published her 1974 bestseller Kōcha Kinoko Health Methods. China had been drinking the tea, under the name hǎibǎo, before the 1940s. Even so, a national craze did not arrive until the 1980s, a result of the Japanese craze of the 1970s. That boom faded amid warnings about kojic acid, reports of contamination in home-made cultures, and too little capacity for industrial production.

  Chen Jin-Shu of National Chung Hsing University recalled that Taiwanese households briefly brewed it in the 1960s under the name hóngchá gū. In the early 21st century, kombucha grew popular in the United States. Its fame in the West now outstrips its fame in China, although drinking is rising in many East Asian countries.

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• 5. A Borrowed Name

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  Merriam-Webster's Dictionary suggests that the English word kombucha arose from a misapplication of Japanese terms such as konbucha and kobucha, which mean tea made from kelp. In Japanese, konbu is an edible kelp from the family Laminariaceae. Kelp tea is a completely different beverage from fermented tea. The American Heritage Dictionary offers another possibility, that the name came from the gelatinous film resembling seaweed. The earliest known English use of the word appears in the British Chemical Abstracts in 1928. Even so, the true etymology remains uncertain.

  The Chinese names are more descriptive. Hǎibǎo, meaning sea treasure, was the historical name, inspired by the culture's resemblance to a jellyfish. Wèibǎo, meaning stomach treasure, pointed to its supposed medicinal benefits. Today the common term is hóngchá jūn, meaning red tea fungus, which follows the Japanese kōcha kinoko. In Taiwan, kāngpǔ chá is more common, a term built from the English name.

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• 6. Bottled and Sold

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  In the late 1990s, commercially bottled kombucha first became available. Because its alcohol level stays under 0.5 percent, it is not federally regulated in the United States. That threshold became a problem in 2010, when elevated alcohol levels were found in many bottled products. Retailers including Whole Foods temporarily pulled the drinks from their shelves. Suppliers responded by reformulating their products to contain less alcohol. Before 2015, some brands were again found to exceed the 0.5 percent line, and that sparked the development of new testing methods.

  By 2014, US sales of bottled kombucha reached $400 million. Of that, $350 million came from Millennium Products, Inc., the company behind GT's Kombucha. That same year, several kombucha makers formed a trade organization called Kombucha Brewers International. In the United States, sales of kombucha and other fermented drinks rose by 37 percent in 2017. Beer companies such as Full Sail Brewing Company and Molson Coors Beverage Company now make kombucha themselves or through subsidiaries.

  Restaurants and pubs helped drive sales in developed countries by marketing kombucha as an alternative to beer and other alcoholic drinks. By 2021 the drink had some popularity in India's National Capital Region, partly because of its success in the West. The market research firm Grand View Research expects the global market to keep growing through 2030.

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• 7. Claims and Risks

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  A review of the research found only one human study on kombucha, even though the drink is promoted for everything from hemorrhoids to cancer. Supporters credit the tea itself, along with fermentation products such as glucuronic acid, acetic acid, polyphenols, and B-complex vitamins like folic acid. No clinical proof shows that it provides any benefit. The review called kombucha an "extreme example" of an unconventional remedy, given the gap between its wide-ranging claims and its potential risks. It concluded that the claims did not outweigh the known risks. It placed kombucha in a class of "remedies that only seem to benefit those who sell them".

  The American Cancer Society said in 2009 that "serious side effects and occasional deaths have been associated with drinking Kombucha tea." A 2003 review found that reports of adverse effects are rare but may be underreported. Home brewing carries a particular danger, because harmful microorganisms can contaminate the tea during preparation. Low acidity matters for safety. Clostridium botulinum, the bacterium behind botulinum toxin, struggles to multiply below pH 4.6.

  Reported adverse effects include severe liver and kidney toxicity as well as metabolic acidosis. Some studies have found usnic acid, a liver toxin, in kombucha. It is not known whether cases of liver damage came from usnic acid or from some other toxin. Over-fermented tea can be acidic enough to cause acidosis, so brewers are cautioned against leaving it too long.

  The acid also threatens teeth. Kombucha falls below the critical pH of tooth enamel, which is approximately 5.5, and that can erode the enamel and lead to decay. Commercial brands can be high in sugar. The British Heart Foundation says added sugars in flavoured kombucha can make blood sugar rise more quickly. It adds that too much sugar can lead to weight gain, which raises the risk of a heart attack or stroke.

  Kombucha is not recommended for people with poor immune function, for women who are pregnant or nursing, or for children under 4 years old. Its small alcohol level also rules it out alongside certain drugs. A 2019 review listed possible risks including hyponatremia, lactic acidosis, and toxic hepatitis. It still said "kombucha is not considered harmful if about 4 oz 120 mL per day is consumed by healthy individuals". Its warnings centered on low pH brews that leach heavy metals from containers.

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• 8. Beyond the Glass

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  A dried kombucha culture becomes a leather-like material known as microbial cellulose. It can be molded onto forms to make seamless clothing. Growing the culture in coffee, black tea, or green tea produces textiles of different colors, and plant-based dyes can change the color further. The growth medium and the dye also alter the feel and texture of the finished cloth. Dried and processed SCOBY has been investigated as a substitute for leather.

  The SCOBY can also be dried and eaten as a sweet or savory snack. Researchers have even put kombucha to industrial use. It can be used for bioleaching, which pulls yttrium oxide out of the phosphors in waste fluorescent lamps.

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