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, or by the acronym SCOBY (for "Symbiotic Colony of Bacteria and Yeast"), it is clinically known as a fungus.
The recorded history of this drink dates back to the Qin Dynasty in China (around 250 BC). The Chinese called it the "Immortal Health Elixir," because they believed Kombucha balanced the Middle Qi (Spleen and Stomach) and aided in digestion, allowing the body to focus on healing. Knowledge of kombucha eventually reached Russia and then Eastern Europe around the Early Modern Age, when tea first became affordable by the populace.
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. The US Food and Drug Administration has no findings on the effects of kombucha. 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 alkaline 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.
Kombucha is also low in calories, and thus a good alternative to other (fermented and non fermented) beverages such as beer, lemonade, and fruit juice . Because of this, home production of kombucha is increasing in popularity.
Advocates believe that kombucha helps by competing with endogenous microbes without toxic constituents, when it is cultivated carefully. Increased glucuronic acid conjugates in the urine after kombucha consumption may support this hypothesis.
Early chemical analysis of kombucha brew suggested that glucuronic acid was a key component of it, perhaps assisting the liver by supplying more of the substance during detoxification. But more recent analysis of kombucha offer a different explanation, as outlined in the book in Analysis of Kombucha Ferments by Michael Roussin. 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 any concentration.
But Roussin suggests that another component may have health benefits
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.
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) are dish soap clean so as not to contaminate the kombucha. For safety reasons, Kombucha should be brewed in food-grade glass containers only. Kombucha should not be brewed in lead crystal, ceramic, plastic, painted, or metallic containers including stainless steel, as the acidic solution can leach by-products into the finished product. Keeping cultures covered and in a clean environment also reduces the risk of introducing contaminants and bacteria.
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 4.5. A pH of less than 2.5 makes the drink too acidic for human consumption, while a pH greater than 4.5 increases the risk of contamination. Use of fresh "starter tea" and/or 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.
If mold does grow on the surface of the kombucha pellicle, or "mushroom," it is best to throw out the batch and start over.