Making kombucha, an excerpt from 'The Art of Fermentation'

Kombucha: Panacea or Peril?

Kombucha is sugar-sweetened tea fermented by a community of organisms into a delicious sour tonic beverage, sometimes compared to sparkling apple cider. Kombucha is typically produced by a SCOBY, also known as a mother, that takes the form of a rubbery disk, which floats on the surface of the tea as it ferments. The community of organisms can also be transferred via the kombucha liquid itself, which can generate a new SCOBY. The kombucha mother closely resembles a vinegar-making by-product, mother-of-vinegar, and is composed of many of the same organisms; indeed, some analysts have come to the conclusion that they are exactly the same.

No other ferment even approaches kombucha in terms of its sudden dramatic popularity (at least in the United States). Kombucha has enjoyed acclaim in many varied locales, widely promoted as beneficial to health, notably in Central and Eastern Europe over the course of the last century, and its use has been growing in the United States since at least the mid-1990s. I first tried kombucha around 1994, when a friend of mine with AIDS started making and drinking it as a health practice. It was touted as a general immune stimulant, though claims of kombucha's benefits have been extraordinarily varied and broad. In those days, kombucha was not commercially available in the United States, but it spread exclusively through grassroots channels as enthusiasts grew more and more mothers and sought to share them. Today there are dozens of commercial enterprises manufacturing and selling kombucha--ranging from small start-ups to multinational corporations. In 2009, a leading US brand, GT's Kombucha, sold more than a million bottles, and Newsweek reports that between 2008 and 2009, US kombucha sales quadrupled, from $80 million to $324 million.

Kombucha has inspired much polarized debate, with claims of dramatic curative properties matched by dire warnings of potential dangers. My own conclusion is that both sets of claims tend to be exaggerated. Kombucha is neither panacea nor peril. Like any ferment, it contains unique metabolic by-products and living bacterial cultures that may or may not agree with you. Try some, starting with small servings, and see how it tastes and feels to you.

Many enthusiasts regard kombucha as something of a miracle cure-all. Harald W. Tietze, an Australian promoter of kombucha, writes that he has received reports of kombucha being used to effectively treat disorders including arthritis, asthma, bladder stones, bronchitis, cancers, chronic fatigue syndrome, constipation, diabetes, diarrhea, edema, gout, hay fever, heartburn, high blood pressure, high cholesterol, kidney problems, multiple sclerosis, psoriasis, prostate disorders, rheumatism, sleeping disorders, and stomach and bowel disorders. Herbalist Christopher Hobbs recorded the following additional claims from discussions on an Internet bulletin board: Kombucha is said to cure AIDS, eliminate wrinkles and remove liver spots, reduce hot flashes during menopause, and help muscle aches, joint pains, coughs, allergies, migraine headaches, and cataracts. While people suffering from each of these conditions may indeed feel that their conditions improved by drinking kombucha, "there is no scientific data to back up any of these claims," writes Hobbs. We cannot expect foods to be panaceas.

One common explanation for the healing power of kombucha is that it contains glucuronic acid, a compound produced in our livers, which binds with various toxins for elimination. Günther Frank, a German promoter of kombucha's health benefits, explains: "Kombucha does not target a specific body organ but, rather, influences the entire organism positively by ... the detoxifying effect of its glucuronic acid." Unfortunately, repeated laboratory analysis has found that glucuronic acid is not actually present in kombucha. Possibly it has been confused with a related compound that is a metabolic by-product of glucose, gluconic acid, which is commonly found in ferments and other foods. In 1995, a small group of kombucha enthusiasts began investigating kombucha chemistry through laboratory testing. One of them, Michael R. Roussin, explains: "Conflicting reports of the ferments' contents, along with a warning from the FDA, prompted me to take a closer look at what I was drinking." After performing mass spectral analysis, specifically looking for glucuronic acid, on 887 different samples of kombucha, the group concluded that the compound was not present.

As for kombucha's potential danger, in 1995 the US Centers for Disease Control (CDC) publication Morbidity and Mortality Weekly Report ran a story headlined, "Unexplained Severe Illness Possibly Associated with Consumption of Kombucha Tea," with possibly being the operative word. In two separate incidents, weeks apart, two women in Iowa had very different unexplained acute health episodes. One of them died. Both drank kombucha daily and made it from the same original SCOBY. The Iowa Department of Public Health immediately issued a warning to stop drinking kombucha "until the role of the tea in the two cases of illness has been evaluated fully." But they were never able to explain how kombucha may have been related to the illnesses, and 115 other people were identified who drank kombucha from the same mother without problems. When the mothers and the kombucha that possibly made the women sick were subjected to microbial analysis, "no known human pathogens or toxin-producing organisms were identified."

Other medical reports have associated extremely varied symptoms with kombucha consumption, also without identifying any specific toxicity or causative factor. Responding to a flurry of questions following the CDC report, the US Food and Drug Administration (FDA) issued a warning of sorts, cautioning that the acidity of kombucha could potentially leach lead or other toxins from vessels, and that "home-brewed versions of this tea manufactured under non-sterile conditions may be prone to microbiological contamination." However, like other investigations, FDA microbial analysis found "no evidence of contamination."

Concern about kombucha's safety has not been limited to government regulators. Mycologist Paul Stamets published an article in 1995 called "My Adventures with 'The Blob.'" Because kombucha was mistakenly referred to as a mushroom, Stamets received frequent questions about it. As an expert in propagating and investigating isolated fungal species, a largely uninvestigated mixed culture worried him. "I personally believe it is morally reprehensible to pass on this colony to sick or healthy friends when, to date, so little is known about its proper use," he writes. "Making Kombucha under non-sterile conditions becomes, in a sense, a biological form of Russian Roulette." While I have tremendous respect for Stamets's work with fungi, I reject the notion that making kombucha at home is random or dangerous. All of the ferments, kombucha included, involve creating selective environments to ensure success. The idea that kombucha (or any ferment) is safe only in the hands of technical experts denies the long lineages of home and village production that spawned them and plays right into the disempowering cult of specialization. Make sure you understand the parameters of the selective environment you need to create, and you are not playing Russian roulette. Basic information and awareness are important. Empowered with them, you may ferment without fear.

Making Kombucha

Kombucha is usually just sugar-sweetened tea, fermented by a specific community of bacteria and yeasts. Increasingly, creative kombucha makers have been giving kombucha exciting new twists by adding herb, fruit, or vegetable flavors. Typically these flavorings are added to kombucha for a secondary fermentation following a primary fermentation of just tea and sugar.

By tea, I mean an infusion made from the tea plant (Camellia sinensis), not the infusions of other plants (such as chamomile or mint) that in the English language we also describe as teas. You may use black tea, green tea, white tea, kukicha, pu-er, or other styles of tea, but in general stay away from Earl Grey or other heavily flavored or scented teas, as the added essential oils may inhibit fermentation. You may use tea bags or loose tea, and brew the tea strong or weak, as you like. I typically brew a very strong concentrate, then dilute and cool it by adding water, so I can add the SCOBY without having to wait for the tea to cool.

To sweeten the tea, add sugar, meaning sucrose from sugarcane or sugar beets. Some people have reported excellent results making kombucha using honey, agave, maple syrup, barley malt, fruit juice, and other sweeteners; others have had their SCOBYs shrivel up and die. Similarly, some people report excellent results without any tea whatsoever, using herbal infusions or fruit juices as the sole flavorings. This leads me to the conclusion that there are divergences on the kombucha family tree. Just as some people, animals, and plants can adapt better than others to altered conditions, some kombucha mothers exhibit greater flexibility and resilience than others. I would encourage you to experiment with different sweeteners and flavorings if you like, but don't use your only mother. Use one layer of the SCOBY to experiment, while maintaining the other in the traditional sugar and tea medium. Try for a few generations, to make sure the mother grows and continues to thrive. The amount of sweetener may vary with your taste. Personally, I never measure the sugar, simply adding to taste. Try about 1/2 cup/125 ml (by weight 4 ounces/113 g) of sugar per quart/liter. Stir well to dissolve; this is easiest if the sugar is added to the tea while still hot. Taste and adjust the sweetness as desired.

Cool the sweetened tea to below body temperature. As described earlier, making a tea concentrate and diluting it with cold water is a fast way to do this. Place sweetened tea into a wide-mouth fermentation vessel, ideally glass or ceramic (with a non-lead glaze). Avoid metal vessels, even stainless steel, which may corrode in the prolonged presence of acids. Because kombucha is an aerobic process, in which fermentation occurs on the surface where oxygen is available, it is best to use a wide vessel only partially full, so as to maximize surface area in relation to volume.

To the cooled sweetened tea, add some mature kombucha, at a ratio of about 5 to 10 percent of the volume of the sweet tea. This both acidifies the tea and contributes kombucha organisms. Acidification is important for maintaining a selective environment that favors the kombucha organisms and prevents potential contaminants from developing. (If for some reason you do not have any mature kombucha to use as an acidifier, use vinegar of any kind, but in a much smaller proportion--about 2 tablespoons/30 ml per quart/liter.) Once you have combined cooled tea, sugar, and mature kombucha in the fermentation vessel, add the mother.

Ideally, the mother will float at the surface. Sometimes it will sink at first, then slowly float back up. Other times one edge of it will float to the surface and generate a new film over the surface. If your SCOBY fails to float or generate a new film after a few days, it is no longer viable. If your SCOBY is a different size or shape from the surface of the kombucha in your vessel, it will generate a new film that is exactly the size and shape of the surface. Always cover the vessel with a light porous cloth that allows air circulation while keeping flies and mold spores off the kombucha. Leave the vessel to ferment in a warm spot, away from direct sunlight.

You can purchase a mother, or obtain one from another home kombucha maker via online trading posts (see Resources), or grow one from commercially available live-culture kombucha. To grow one, simply pour a bottle of kombucha--preferably plain, without any particular flavoring--into a wide-mouth jar, cover with a cloth, and wait about a week (longer in cool temperatures) for a skin to form on the surface. This skin is a kombucha SCOBY.

As you make more kombucha with your SCOBY, it will get thicker, generally growing in layers that you can peel off and use to start additional batches of kombucha, or share. I've seen kombucha mothers as thick as about 6 inches/15 cm. There is no particular benefit to a huge SCOBY, so most people peel away layers and share them. Other uses I have seen or heard of for extra SCOBYs include these:

Blend them into a paste and use them for facials, spreading the paste on your face and leaving it to dry there.

Brooke Gillon of Nashville, Tennessee, folds thin layers of kombucha SCOBYs into flower shapes and dries them in that shape. Gorgeous!

Suzanne Lee, of the School of Fashion and Textiles in London, makes garments out of kombucha. According to a news report: "As the sheets dry out, overlapping edges 'felt' together to become fused seams. When all moisture has evaporated, the fibers develop a tight-knit, papyrus-like surface that can be bleached or stained with fruit and vegetable dyes such as turmeric, indigo, and beetroot."

Several people have reported stretching kombucha SCOBYs and vinegar mothers onto frames and painting on them. They are composed of a cellulose, just like paper.


Kombucha does best in a warm environment, from 75° to 85°F/24° to 30°C. The length of fermentation will vary depending upon specific temperature, and how acidic you like it. In warm weather, I typically ferment my kombucha about 10 days. Taste it every few days, and evaluate whether you want it to continue to ferment and acidify. In a cool space--say, 60°F/16°C--it takes a very long time; sometimes in winter I have left mine for months before it acidified to my liking. Once kombucha has become as acidic as you like (only you can be the judge of that), remove the SCOBY, transfer the kombucha to bottles--reserving some to acidify the new batch--and brew more sweet tea to begin the process anew. Kombucha works best as an ongoing rhythm, because to remain alive, the SCOBY needs continual nourishment. If you go away, you can simply leave the SCOBY in kombucha for as long as several months, and then resume feeding it fresh sweetened tea upon your return.

When your kombucha is pleasingly acidified, you have several options. The simplest is to drink it. Bottle it as is and refrigerate. If you wish to further flavor, you can add fruit or vegetable juice, or a sweetened herbal infusion or decoction, for a secondary fermentation. The most exciting kombuchas I've tried have been made in this fashion. When I visited my friends at the Cultured Pickle Shop in Berkeley for a veritable tasting orgy, I was blown away by their incredible innovative kombucha flavors: Buddha's hand (a citrus fruit), mint, and bee pollen; turnip (oh, so good!); and beet. They do the primary fermentation with green tea and sugar with the kombucha mother; then decant kombucha and mix with fruit or vegetable juice for a secondary fermentation; and finally mix with a bit of honey at bottling for carbonation.

The secondary fermentation may be aerobic in an open wide-mouth vessel like the primary fermentation, or in a sealed or air-locked vessel. In an open vessel, the sweetened kombucha will likely develop a new mother on the surface, and growth will continue to be dominated by acetic acid organisms. In a sealed vessel (which could be the final bottle for serving, or not), the secondary ferment will yield more alcohol, as well as lactic acid.

Even if you don't care to incorporate additional ingredients in a secondary fermentation, you can carbonate kombucha in bottles. Simply decant it into sealable bottles while it is still a bit on the sweet side; seal the bottles; and allow it to continue to ferment in the sealed bottles for a few more days so carbonation can develop. Add a bit of fresh sweetener at bottling to speed or increase carbonation, but beware of excessive carbonation. I can't caution readers enough on this subject.

Questions continually arise as to whether sugar and caffeine persist in mature kombucha. The sugars do metabolize into acids, so you could ferment kombucha to the point that there is no sugar left. However, at that point, your kombucha would taste like vinegar, and most people prefer it when it is still somewhat sweet, and hence still with some of the sugar intact. As for caffeine, when herbalist Christopher Hobbs submitted a sample of kombucha to a laboratory for analysis, it was found to contain 3.42 mg/100 ml--much less than is typically found in a cup of tea, but most definitely present.39 Michael Roussin reports that according to his laboratory analyses, caffeine levels remain constant throughout the kombucha fermentation period.40 Specific caffeine levels will vary with type and amount of tea, length of steeping, and so forth. The notion that kombucha removes caffeine from tea is unsubstantiated; if you wish to avoid caffeine, make kombucha using weak or decaffeinated tea.

Another issue that has come up in relation to kombucha is its alcohol content. Kombucha probably always contains small traces of alcohol, as do nearly all fermented foods, including sauerkraut. Typically, the alcohol content of kombucha is somewhere below 0.5 percent by volume, which is considered a non-alcoholic beverage by law. (Traces of alcohol below 0.5 percent are typically found in fruit juices, sodas, "non-alcoholic" beers, and even breads and bread products.41) Sometimes, however--especially with anaerobic in-bottle secondary fermentation--kombucha's alcohol content can rise above the 0.5 percent legal limit. In June 2010, the US Alcohol and Tobacco Tax and Trade Bureau (TTB) tested off-the-shelf samples of various commercial kombucha products and found that, in some, alcohol levels exceeded the allowed 0.5 percent. TTB issued a "guidance document" declaring that "kombucha products containing at least 0.5 percent alcohol by volume are alcohol beverages."42 Many retailers removed kombucha from their shelves until greater product control could be assured. Some manufacturers are taking measures to limit opportunities for in-bottle fermentation; others are switching from traditional kombucha to laboratory-derived defined starter cultures.

Finally, a word of caution about molds that sometimes develop on kombucha SCOBYs. I have experienced mold developing on kombucha, and I simply removed the SCOBY from the kombucha, scraped or peeled the mold away, rinsed the SCOBY, and proceeded to drink the kombucha and reuse the SCOBY, without incident. However, after reading Paul Stamets's article on kombucha, I would advise greater caution. "Of most concern are the species of Aspergillus I have found floating around with Kombucha," Stamets writes. (In contrast with Aspergillus oryzae and A. sojae, used for millennia to make rice beer, miso, soy sauce, and many other ferments, some Aspergillus species produce toxins.) "I fear that amateurs could think that by merely pulling out the Aspergillus colonies with a fork, that the culture would be de-contaminated, a dangerous, even deadly presupposition. The water-soluble toxins of Aspergillus can be highly carcinogenic."43 Avoid molds by remembering to acidify each batch of kombucha with mature acidified kombucha from the previous batch. In the absence of mature kombucha, you can use some vinegar. If molds should form, however, discard the batch of kombucha, as well as the SCOBY, and begin anew with a new SCOBY.



Doesn't start to ferment

It may be that your starter is not viable. It may be that the solution was too hot when culture was introduced and killed it. Maybe ambient temperatures where you placed your starter are too cold; try to find a warmer spot. Maybe chlorinated water is inhibiting fermentation. In the case of ginger bug, maybe the ginger was irradiated; try again with organic ginger. If there was no starter other than fruit: Stir, stir, stir. And be patient.

Gets too sour

This means you have fermented it too long. Try a shorter fermentation next time. Many beverages, however, notably kombucha, can be used as vinegar if they overly acidify. In addition, many overly soured beverages can be salvaged by diluting with some water or carbonated water, along with sweetener if desired.

Too weak

Next time, use more of the flavoring agent (ginger, tea, sweet potato, mauby bark, fruit, whatever) and/or sugar.

Surface molds develop

Acidifying kombucha with mature kombucha or vinegar helps prevent surface molding. With ferments other than kombucha, stirring or shaking daily while they are in open vessels prevents molds by disturbing them before they become visible. In making vinegar, stir the sugary solution at least daily until a mother forms. After that, increasing acidity will help protect the vinegar from molding, and stirring becomes impossible without disturbing the mother.

Kombucha mother sinks

Sometimes when you place a kombucha mother into a new batch of cooled, sweetened tea, the mother sinks to the bottom rather than floating on the surface. Be patient. Often within a few hours the mother will float to the top. If not, sometimes one edge of the mother will float to the top, causing a new mother to be generated, which at first looks like a thin film over the surface. If neither of these things happens, and your mother remains sunken in the sweet tea, it is no longer viable as a kombucha mother. Make it into nata candy and find another mother, or culture your kombucha with a high proportion (one-quarter to one-half) of mature kombucha, and it will generate a new mother on its surface.

Straining bread for kvass is difficult

The hardest part of making kvass is squeezing out all the liquid that absorbs into the bread. Strain the bread-water solution through a colander lined with a couple of layers of cheesecloth. Each time the colander fills with bread, gather the edges of the cheesecloth together, twist to wring out the liquid, and then knead the ball of cloth-encased soggy bread from different angles, trying to force out as much liquid as you can. Don't worry too much about forcing out every last bit.

Water kefir grains not growing

Water kefir grains typically grow pretty rapidly. Under ideal conditions, they can more than double with each feeding. If you find that yours are not growing, it probably means that they are no longer viable. Water kefir grains can become pickled if they are left more than a few days in an acidified solution without fresh sugar. When you find some more water kefir grains, feed them more frequently to avoid this.

Water kefir grains disappear

See above. If water kefir grains are left in an acidified solution without fresh sugar, they first become pickled, then may eventually disappear.

(Lynne's interview with Sandor Katz)

Excerpted from The Art of Fermentation by Sandor Ellix Katz (Chelsea Green, 2012), with permission of the publisher. To read more about this book and the author, visit


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