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Kombucha is a fermented tea that is imbibed for medicinal purposes, although there is currently no specific scientific information supporting any purported benefits. Kombucha is available commercially, but can be made at home by fermenting tea using a visible solid mass of microorganisms called a kombucha culture or mushroom.

Biology of kombucha

The culture contains a symbiosis of Acetobacter (acetic acid bacteria) and yeast, mostly Brettanomyces bruxellensis, Candida stellata, Schizosaccharomyces pombe, Torulaspora delbrueckii and Zygosaccharomyces bailii.

The culture itself looks somewhat like a large pancake, and though often called a mushroom, a mother of vinegar or by the acronym SCOBY (for "Symbiotic Colony of Bacteria and Yeast"), it is scientifically classified as a zoogleal mat.

History and names

The recorded history of kombucha began in Ukraine and Russia during the late 19th century. In Russian, the kombucha culture is called čajnyj grib чайный гриб (lit. "tea mushroom"), and the drink itself is called grib гриб ("mushroom"), "tea kvass" квас, or simply kvass, which differs from regular kvass traditionally made from water and stale rye bread.

Some promotional kombucha sources propagate falsehoods that the history of this tea-based beverage originated in ancient China or Japan, but in both cases centuries prior to knowledge of tea (see history of tea in China and history of tea in Japan). One author claims kombucha, famously known as the "Godly Tsche [i.e., tea]" during the Chinese Qin Dynasty (221-206 BCE), was "a beverage with magical powers enabling people to live forever". There are no recorded references to either tea or "godly tea" during the Qin dynasty. Another author claims an etymology from "a Korean doctor named Kombu treated the Japanese Emperor Ingyō in 415 A.D." The early Japanese history Kojiki does mention an envoy from the ancient Korean state Silla who was "deeply versed in the medical art" and cured the Emperor's sickness – but his name was 金武, which is pronounced Korean Kim/Gim Mu or Japanese Kin/Kon Mu.

Components

Kombucha contains many different cultures along with several organic acids, active enzymes, amino acids, and polyphenols.  For the home brewer, there is no way to know the amounts of the components unless a sample is sent to a laboratory. Kombucha, has been safety-checked by The US Food and Drug Administration . Final kombucha may contain some of the following components depending on the source of the culture: Acetic acid, which provides much anti-microbial activity; butyric acid, gluconic acid, glucuronic acid, lactic acid, malic acid, oxalic acid, usnic acid, as well as some B-vitamins.

Due to the acidic fermentation process used in its brewing, Kombucha contains ethyl alcohol in amounts that vary from 0.5% to 1.5%, depending on anaerobic brewing time and proportions of microbe. Commercial preparations are typically 0.5% for distribution and safety reasons.

Additionally, some tea makers offer a dried version of kombucha, mixed with the tea leaves, that dissolves in hot water.

Health Claims

Kombucha proponents claim many advantages such as increased energy, sharper eyesight, better skin condition, and better experience with foods that 'stick' going down such as rice or pasta.

A review of the published literature on the safety of kombucha suggests no specific oral toxicity in rats, although it has also been shown to increase the size of both the liver and spleen in mice. While no randomized case-controlled studies have been published in humans, several case reports have suspected liver damage, metabolic acidosis, cutaneous anthrax infections and life-threatening toxicity. Other reports suggest that care should be taken when taking medical drugs or hormone replacement therapy while regularly drinking kombucha. It may also cause allergic reactions.

Other health claims may be due to the simple acidity of the drink, possibly influencing the production of stomach acids or modifying the communities of microorganisms in the GI tract.

Scientific Claims

Health claims for kombucha focus on a chemical called glucuronic acetate, a compound that is used by the liver for detoxification. The idea that glucuronic acid is present in kombucha is based on the observation that glucuronic acid conjugates (glucuronic acid + waste chemicals) are increased in the urine after consumption of kombucha.

Early chemical analysis of kombucha brew suggested that glucuronic acid was the key component, and researchers hypothesized that the extra glucuronic acid would assist the liver by supplying more of the substance during detoxification. These analyses were done using gas chromatography to identify the different chemical constituents, but this method relies on having proper chemical standards to match to the unknown chemicals.

A more recent and thorough analysis, outlined in the book in Analysis of Kombucha Ferments by Michael Roussin suggests a different explanation. Roussin reports on an extensive chemical analysis of a variety of commercial and homebrew versions of kombucha, and finds no evidence of glucuronic acid at all. These scientific measurements contradict the earlier studies and conflict with the original hypothesis.

Instead, Roussin discovered that the active component in kombucha is most likely glucaric acid. This compound, also known as D - glucaro -1,4 lactone, helps in the elimination of glucuronic acid conjugates that are produced by the liver. When glucuronic acid conjugates are disposed in the bowel during the elimination process, normal gut bacteria can break up these conjugates using an enzyme called beta-glucuronidase. Glucaric acid is an inhibitor of this bacterial enzyme, so the end result is that the glucuronic acid + waste is properly eliminated the first time, rather than being reabsorbed and detoxified over and over. Thus, glucaric acid probably makes the liver more efficient.

Interestingly, glucaric acid is commonly found in fruits and vegetables, and is being explored independently as a cancer preventive agent. It has also been discovered that the bacterial beta-glucuronidase enzyme can interfere with proper disposal of a chemotherapeutic agent, and that antibiotics against the gut microbiota can prevent toxicity of some chemotherapy drugs.

Reports of adverse reactions may be related to unsanitary fermentation conditions, leaching of compounds from the fermentation vessels, or "sickly" kombucha cultures that cannot acidify the brew. Cleanliness is important during preparation, and in most cases, the acidity of the fermented drink prevents growth of unwanted contaminants. If a culture becomes contaminated, it will most likely be seen as common mold, green or brown in color.

Safety and contamination

As with all foods, care must be taken during preparation and storage to prevent contamination. Keeping the kombucha brew safe and contamination-free is a concern to many home brewers. Key components of food safety when brewing kombucha include clean environment, proper temperature, and low pH.

There is a low rate of homebrew contamination which might be explained by protective mechanisms, such as formation of organic acids and antibiotic substances. Thus, subjects with a healthy metabolism do not need to be advised against cultivating Kombucha. However, those suffering from immunosuppression should preferably consume controlled commercial Kombucha beverages.

In every step of the preparation process, it is important that hands and utensils (anything that is going to come into contact with the culture) be dish soap clean so as not to contaminate the kombucha. Kombucha becomes very acidic (in the neighborhood of pH 3.0 when finished) and so can leach unwanted and potentially toxic material from the container in which it is fermenting. Food-grade glass is very safe. Gunther Frank says on his website that besides glass, acceptable containers include china, glazed (without lead) earthenware, stainless steel and food-grade high density polyethylene (HDPE) and polypropylene (PP). Keeping cultures covered and in a clean environment also reduces the risk of introducing contaminants and insects.

Maintaining a correct pH is an important factor in a home-brew. Acidic conditions are favorable for the growth of the kombucha culture, and inhibit the growth of molds and bacteria. The pH of the kombucha batch should be between 2.5 and 4.6.  A pH of less than 2.5 makes the drink too acidic for normal human consumption, while a pH greater than 4.6 increases the risk of contamination. Use of fresh "starter tea" and/or distilled vinegar can be used to control pH. Some brewers test the pH at the beginning and the end of the brewing cycle to ensure that the correct pH is achieved and that the brewing cycle is complete.

If mold does grow on the surface of the kombucha culture, or "mushroom," it is best to throw out both culture and tea and start again with a fresh kombucha culture.

Kombucha mother and the symbiotes

The Kombucha Mother, shown in a square shape, is not unlike the thickness of a well risen pancake, and takes the shape of its container. It is a rapidly multiplying bacterial mass floating atop a yeast filled fluid. The bacteria are of the genus Mycoderma (Greek for fungus skin). The yeast below are involved in fermenting and receive oxygen for this process, passed by the bacteria. Acetic acid is created by the yeast, hence the second, title word Aceti (Latin for of the acid). Kombucha is "Mycoderma Aceti". Kombucha is "mother of acid".

"Kombucha tea" is a homemade drink of the living medium of Kombucha. Kombucha contains both bacteria and yeasts. Normally these two microorganisms are at odds with one another, but in this case there is a symbiosis. It is able to repel other organisms such as molds and bacteria that would normally contaminate such a long-standing culture. It keeps its liquid's pH low to accomplish this.

The lake of black tea has been highly sweetened with sugar.

Brew

Black Tea is the medium of the mother. Sugars assist fermentation. The sweet brew is poured over the mother, and the container covered with a porous cloth to deter dust and organisms. After a week or two of fermentation, during which frequent samples are taken to taste for some desired balance between sweet and sour, the liquid is tapped, but at least some liquid is retained to keep the pH low to deter contaminant microorganisms. The process repeats itself indefinitely, and the mother will eventually produce a "daughter", which can easily be directly handled, separated like two pancakes, and moved to another container if desired.

The yeast in the tapped liquid will then continue to live. A second wait time for about a week produces more carbonation. Left alone the Kombucha settles into months of production time (producing daughters perhaps), creating an ever more acidic and vinegar-dominated cider. At any point the Kombucha can be checked for daughter or tapped or have tea added. An amount of liquid from the previous batch will preserve some yeast and help maintain a low pH environment for the mother.