Kombucha

Kombucha (also tea mushroom, tea fungus, or Manchurian mushroom when referring to the culture; botanical name Medusomyces gisevii Lindau ) is a fermented, slightly alcoholic, lightly effervescent, sweetened black or green tea drink commonly intended as a functional beverage for its supposed health benefits. Sometimes the beverage is called kombucha tea to distinguish the name from the kombucha culture of bacteria and yeast.

Kombucha is produced by fermenting tea using a symbiotic culture of bacteria and yeast (SCOBY) commonly called a mother or mushroom. The microbial populations in a SCOBY vary: the yeast component generally includes Saccharomyces cerevisiae, along with other species; while the bacterial component almost always includes Gluconacetobacter xylinus to oxidize yeast-produced alcohols to acetic acid (and other acids). Although a SCOBY is commonly called tea fungus or mushroom, those terms are misleading; the culture is actually "a symbiotic growth of acetic acid bacteria and osmophilic yeast species in a zoogleal mat [biofilm]". The living bacteria are said to be probiotic, one of the reasons for the drink's popularity.

The exact origins of kombucha as a drink are not known. It is thought to have originated in the area of Northeastern China, and was traditionally consumed there, but also in Russia and eastern Europe. Kombucha is now homebrewed in the US, and globally, and is also sold commercially by various companies.

Numerous implausible claims have been made for health benefits from drinking kombucha. These include claims for treating AIDS, aging, anorexia, arthritis, atherosclerosis, cancer, constipation, and diabetes, but there is no evidence to support any of these claims. There have been rare cases of serious adverse effects, including fatalities, from the beverage, possibly arising from contamination during home preparation. The potential harms of drinking kombucha outweigh the unclear benefits, so its use as a therapeutic food is not recommended.

History
The exact origins of kombucha are not known, although Manchuria is commonly cited as a likely place of origin. It may have originated as recently as 200 years ago or as long as 2000 years ago. The drink is reported to have been consumed in east Russia at least as early as 1900 and from there entered Europe. Its consumption increased in the United States during the early 21st century. Having an alcohol content of less than 0.5%, kombucha is not a federally regulated beverage in the United States. Prior to 2015, some commercially available kombucha brands were found to contain alcohol content exceeding this threshold, sparking the development of new testing methods.

Etymology
The word kombucha is of uncertain etymology, but may be a case of a misapplied loanword from Japanese. In Japanese, the term "kelp tea" (昆布茶) refers to a completely different beverage; the kelp tea, made from dried and powdered konbu (an edible kelp from the Laminariaceae family). The term for the fermented tea in Japanese, is "fungus tea" (紅茶キノコ). The American Heritage Dictionary suggests that it is probably from the "Japanese kombucha, tea made from konbu (the Japanese word for kelp perhaps being used by English speakers to designate fermented tea due to confusion or because the thick gelatinous film produced by the kombucha culture was thought to resemble seaweed)." Writings about the beverage in Japanese generally take the point of view that the Japanese word 'kombucha' was mistakenly applied in English to what Japanese call "kocha kinoko." Cha means tea or o-cha, Japanese green tea.

Kombucha has about 80 other names worldwide. A 1965 mycological study called kombucha "tea fungus" and listed other names: "teeschwamm, Japanese or Indonesian tea fungus, kombucha, wunderpilz, hongo, cajnij, fungus japonicus, and teekwass". Some further spellings and synonyms include combucha and tschambucco, haipao, kargasok tea, kwassan, Manchurian fungus or mushroom, spumonto, as well as the misnomers champagne of life, and chai from the sea.

Biological
A kombucha culture is a symbiotic culture of bacteria and yeast (SCOBY), similar to mother of vinegar, containing one or more species each of bacteria and yeasts, which form a zoogleal mat known as a "mother." The cultures may contain one or more of the yeasts Saccharomyces cerevisiae, Brettanomyces bruxellensis, Candida stellata, Schizosaccharomyces pombe and Zygosaccharomyces bailii. There is a lack of research regarding its biological properties.

The bacterial component of kombucha comprises several species, almost always including Gluconacetobacter xylinus (G. xylinus, formerly Acetobacter xylinum), which ferments alcohols produced by the yeasts into acetic and other acids, increasing the acidity and limiting ethanol content. The population of bacteria and yeasts found to produce acetic acid has been reported to increase for the first 4 days of fermentation, decreasing thereafter. G. xylinus has been shown to produce microbial cellulose, and is reportedly responsible for most or all of the physical structure of the "mother", which may have been selectively encouraged over time for firmer (denser) and more robust cultures by brewers.

The mixed, presumably symbiotic culture has been further described as being lichenous, in accord with the reported presence of the known lichenous natural product usnic acid, though as of 2015, no report appears indicating the standard cyanobacterial species of lichens in association with kombucha fungal components.

Chemical and nutritional
It is made by putting the kombucha culture into a broth of sugared tea. Kombucha tea made with less sugar may be unappealing. Sucrose is converted, biochemically, into fructose and glucose, and these into gluconic acid and acetic acid, and these substances are present in the drink. In addition, kombucha contains enzymes and amino acids, polyphenols, and various other organic acids; the exact quantities of these items vary between preparations. Other specific components include ethanol (see below), glucuronic acid, glycerol, lactic acid, usnic acid (a hepatotoxin, see above), and B-vitamins. Kombucha has also been found to contain vitamin C.

The alcohol content of the kombucha is usually less than 0.5%, but this number increases with elongated fermentation times. Over-fermentation generates high amounts of acids similar to vinegar. The pH of the drink is typically about 2.5.

Production
Kombucha drink is prepared at home globally and some companies sell it commercially. Commercially bottled kombucha became available in the late 1990s. In 2010, elevated alcohol levels were found in many bottled kombucha products, leading retailers including Whole Foods to temporarily pull the drinks from store shelves. In response, kombucha suppliers reformulated their products to have lower alcohol levels.

By 2014 US sales of bottled kombucha were $400 million; $350 million of that was earned by Millennium Products, Inc. which sells "GT's Kombucha". In 2014, the market was projected to have 30% growth, and companies that make and sell kombucha formed a trade organization, Kombucha Brewers International. In 2016, PepsiCo purchased kombucha maker KeVita for approximately $200 million.

Health claims
People drink kombucha for its many purported health benefits. Research has been conducted using biological assays in vitro. Other studies have been in vivo using rats. There have not been any human trials conducted to assess its possible biological effects, and the purported health beneﬁts resulting from its biological activities have not been demonstrated in humans.

In 2000, a scientific review was done, which summarized the range of claimed health benefits: "It has been claimed that Kombucha teas cure asthma, cataracts, diabetes, diarrhea, gout, herpes, insomnia and rheumatism. They are purported to shrink the prostate and expand the libido, reverse grey hair, remove wrinkles, relieve haemorrhoids, lower hypertension, prevent cancer, and promote general well-being. They are believed to stimulate the immune system, and have become popular among people who are HIV positive or have full-blown AIDS".

A 2003 systematic review characterized kombucha as an "extreme example" of an unconventional remedy because of the disparity between implausible, wide-ranging health claims and the potential risks of the product. It concluded that the proposed, unsubstantiated therapeutic claims did not outweigh known risks, and that kombucha should not be recommended for therapeutic use, being in a class of "remedies that only seem to benefit those who sell them."

Adverse effects
Reports of adverse effects related to kombucha consumption are rare, but may be underreported, according to the 2003 review. The American Cancer Society says that "Serious side effects and occasional deaths have been associated with drinking Kombucha tea".

Adverse effects associated with kombucha consumption include severe hepatic (liver) and renal (kidney) toxicity as well as metabolic acidosis. At least one person is known to have died after consuming kombucha, though the drink itself has never been conclusively proved a cause of death.

Some adverse health effects may arise from the acidity of the tea causing acidosis, and brewers are cautioned to avoid over-fermentation. Other adverse effects may be a result of bacterial or fungal contamination during the brewing process. Some studies have found the hepatotoxin usnic acid in kombucha, although it is not known whether the cases of liver damage are due to usnic acid or to some other toxin. Topical use of the tea was associated with anthrax infection in one report, but contamination of the tea may have occurred during storage.

Drinking kombucha can be harmful for people with preexisting ailments. Due to its microbial sourcing and possible non-sterile packaging, kombucha is not recommended for people with poor immune function, women who are pregnant or nursing, or children under 4 years old. It may compromise immune responses or stomach acidity in these susceptible populations.

Other uses
Kombucha culture, when dried, becomes a leather-like textile known as a microbial cellulose that can be molded onto forms to create seamless clothing. Using different broth media such as coffee, black tea, and green tea to grow the kombucha culture results in different textile colors, although the textile can also be dyed using plant-based dyes. Different growth media and dyes also change the textile's feel and texture.