- Kombucha is a fermented tea that can be produced commercially or in private homes. Kombucha has become increasingly popular, and a number of national and regional supermarkets, including natural foods stores and large grocery store chains, now carry the fizzy, refreshing tea on store shelves.
- Many people drink kombucha for its professed health benefits; however, these claims still need more research. Some animal studies have shown it has bioactive components that display antioxidant, detoxifying, and antimicrobial properties that may contribute to claims that kombucha plays a role in overall immune health, mental health, and cancer and cardiovascular disease prevention.
- Kombucha production dates back to as early as 220 B.C., and it is now distributed globally. As of 2019, the brand “GT’s Kombucha” was one of the largest commercial distributors of the drink.
- The FDA states that when properly prepared, kombucha can be safe for human consumption. Reported cases of negative health effects and side effects have been isolated and few. Cases were associated with high acidity and preexisting conditions, overconsumption, poor handling of the fermented product, or the result of not following proper, hygienic home production practices.
Kombucha is a fermented tea product with an acidic taste and a hint of sweetness. It is made from a mixture of brewed tea, sugar, and a culture often referred to as a SCOBY (Symbiotic Culture of Bacteria and Yeast), a mother, or (inaccurately) as a mushroom. The SCOBY is a biofilm-like microbial mat composed of cellulose and a mutually beneficial association of fermentative bacteria and yeasts. The popularity of kombucha can, in large part, be attributed to its perceived health benefits, although the majority of these have not been suitably evaluated. Rich in organic acids and biologically active compounds from fermentation activity, kombucha has a low pH and strong antimicrobial properties, which may provide therapeutic benefits and make kombucha components good natural food preservatives.
Although kombucha has only recently become popular in the United States, there are records of kombucha production from as early as 220 B.C. in northeast China, where it was widely consumed for its presumed detoxifying and energizing abilities. Kombucha then emerged in Japan, in 414 A.D., where it was notably used to aid the emperor with his gastrointestinal health concerns. Dutch and Portuguese explorers brought kombucha to Russia and other European countries at the beginning of the 20th century for use as a medicine. Since then, kombucha tea and culture have become available to consumers worldwide. The first commercially available brand in the United States started small in 1995, yet consumer demand continues to drive constant growth in the industry for both mainstream commercial production and home production.
Although kombucha has never been attributed to a foodborne outbreak, two incidents of severe, unexplained illness potentially linked to kombucha consumption were reported within days of each other in a small community in rural Iowa in 1995. The cases (both female) experienced severe metabolic acidosis with elevated pH and lactic acid levels that resulted in acute respiratory distress; both were hospitalized and went into cardiac arrest. One died. Toxicology tests in both cases ruled out any link to drugs (prescription or nonprescription), carbon monoxide, or cyanide poisoning, nor was there evidence of any septic or cardiogenic cause. However, both cases reported drinking kombucha tea daily for the previous two months, and both had received their SCOBY from the same local supplier. More than 115 community members had also received SCOBYs from the same local supplier, but no other illnesses were reported.
On April 10, 1995, following the second incident, the Iowa Department of Public Health (IDPH) released a public alert recommending that persons avoid consumption of kombucha tea until an investigation into tea’s role in the two illnesses could be completed. The IDPH, CDC, and the Food and the FDA were involved in the investigation. Microbiologic analysis by the FDA of samples from both cases’ SCOBYs (and prepared tea) identified several species of yeast and bacteria but no known human pathogens or toxin-producing organisms. The IDPH and CDC also surveyed a nonrandom sample of 24 members from the community who regularly consumed Kombucha. The results indicated that the incubation regimen and consumption patterns of those surveyed were similar to that of the two cases. Ultimately, no causal link was established between the illnesses of the two women and their consumption of Kombucha tea. However, no explanation for the illnesses was ever discovered.
Kombucha is commonly made with black tea but can also be made with green tea or oolong tea, depending on personal preference. Herbal teas or those with added flavorings are not recommended for the health of the SCOBY culture. To make kombucha, tea leaves or tea bags are added to boiled water and allowed to steep for five to ten minutes. The leaves or bags are then removed, and sugar is dissolved in the brew while it is still hot. The sweetened tea is cooled to ambient temperature, and the SCOBY, plus a small portion of previously-fermented kombucha is added. The addition of previously-fermented kombucha, also called starter liquid, aids in preventing early stage microbial contamination by rapidly reducing the pH of the mixture and providing suspended yeast and bacteria. A fresh SCOBY and starter liquid can either be purchased online via a starter kit, grown from a commercial bottle of raw, unflavored kombucha, or a layer can be – cut from a “mother SCOBY.” The SCOBY will steadily grow to cover the surface area of the fermenting kombucha and take the shape of the container that is it brewed in.
The acidified, sweetened tea and SCOBY are placed in a food-safe glass, plastic, or stainless steel brewing vessel and covered with a clean, fine-weave, porous material (such as a clean coffee filter or towel, but not cheesecloth as the holes are too large to keep out insects and airborne contaminants) and secured with a large rubber band or bungee cord. Kombucha ferments at room temperature, ideally around 72-84°F (22-29°C), out of direct light, for 7-10 days. Then it is generally tasted and either allowed to continue to ferment until the desired flavor or chemical parameters are reached or decanted for consumption. Once it is ready for consumption, kombucha should be decanted, filtered, or the SCOBY removed. Kombucha can be consumed unflavored, or flavorings such as juice, fruit, and herbs can be added as desired. The kombucha can then be carbonated to provide a bubbly character. For safe consumption, the pH must be below 4.2, but not lower than 2.5. During fermentation, the fermenting culture grows in layers on the SCOBY, forming a solid mat on the surface of the liquid. To begin a subsequent kombucha fermentation, the SCOBY and at least 1 cup of the fermented kombucha per every gallon final volume to be prepared, will again be combined with brewed, sweetened tea that has been cooled to room temperature. This can be done as a “continuous brew,” in which about 80% of the finished kombucha is decanted for consumption, while the SCOBY and liquid remain in the vessel and sweetened tea is added for further fermentation. This minimizes handling and contamination of the SCOBY.
Researchers have identified many acetic and lactic acid bacteria and yeasts in both the SCOBY and kombucha liquid, with variability across culture samples. The ecology consists of, at a minimum, the acetic acid bacteria Komagataeibactor xylinus (reclassified from Gluconacetobacter genus), as well as Lactobacillus spp., and yeasts including Zygosaccharomyces spp, Brettanomyces/Dekkera spp., Pichia spp., or Saccharomyces spp.. Cultures sourced from various regions provide varying microbiological diversity. During the fermentation of the sweet tea to kombucha, yeasts first metabolize sucrose to glucose and fructose; the glucose is then used to produce ethanol and carbon dioxide. The major acetic acid bacteria genus found in kombucha is Gluconacetobacter, which contributes to the decrease in pH during the fermentation process by converting glucose to gluconic acid and ethanol into acetic acid.
Komagataeibactor xylinus is responsible for synthesizing glucose into the cellulose that forms the SCOBY, facilitating the environment for the bacteria and yeast to grow in a symbiotic relationship. Acetic acid stimulates the yeast to produce ethanol, and ethanol, in turn, aids acetic acid bacteria to grow and produce acetic acid, decreasing the final alcohol content while increasing the acidity. After this fermentation process, kombucha can be consumed or bottled for distribution.
Production Control Points
Kombucha is categorized as a specialized process in the FDA Food Code, requiring all retail or food service operators planning to sell kombucha to obtain a variance from their regulatory authority and to submit a food safety plan to their regulatory authority as defined in the Food Code section 3-502.11. A Special Report in the Journal of Environmental Health identifies biological and chemical hazards for production analysis and provides guidance to retail manufacturers for a Hazard Analysis and Critical Control Point (HACCP) plan, including the potential for spore-forming bacteria to germinate when tea and sugar are added to boiling water, unwanted pathogen or mold growth, and mycotoxin development, among others. The only significant hazard, however, is the potential for acid-resistant pathogen growth during fermentation. To prevent this, the pH should be continuously monitored using a digital pH meter and recorded to ensure that the pH adequately reduces from about 5 to 4.2 within seven days. If the pH does not reach 4.2 within seven days after culturing, and then to an end point around 2.5, it is an indication of a contaminated culture or a lower than preferred fermentation temperature.
Commercial producers can implement quality control checks throughout their production process to ensure their products safe, consistent, and compliant. These checks can include measuring chemical parameters such as titratable acidity (unit: as g/L as acetic acid), alcohol content (ABV, i.e. % v/v), total sugar or sucrose content (g/100g), and dissolved gases CO2 (g/L or vol) and O2 (ppb). Microbiological checks can also be performed such as total yeast counts, bacteria quantification, and selective media plating to ensure that the yeast and bacteria detected are desired genera.
Commercial production and processes vary across the many kombucha breweries. 2-gallon glass vessels are used at some breweries, while others use food-grade stainless steel tanks up to thousands of gallons in capacity. The timing of tea steeping, fermentation, and aging are not uniform across producers. Some brewers naturally carbonate their kombucha, while others “force carbonate”, a process of adding food-grade CO2 at consistent levels to achieve a desired effervescence. Additionally, the packaging process can take several forms. Kombucha can be packaged in bottles and cans and into kegs to be sold on tap at stores, restaurants, and farmers’ markets.
Good Manufacturing Practices
The FDA has suggested several good manufacturing practices (GMPs) and standard operating procedures (SOPs) for compliance in safe kombucha production. GMPs include using brewing water over 165°F (74°C), keeping equipment clean and sanitary, using a fresh commercially-purchased culture for first brew, not selling kombucha with a pH below 2.5 or higher than 4.2, and discarding kombucha with signs of mold growth. Recommended SOPs include having a precise pH measurement and calibration system as well as properly notifying and instructing employees on the safe production of kombucha according to the FDA guidelines.
Guidance and Regulation
As with many fermented products, a varying amount of alcohol may be present in kombucha. After it is bottled, in the absence of oxygen, the yeast will continue to degrade sucrose to glucose and fructose and is capable of increasing carbonation and producing alcohol levels greater than 0.5%. The alcohol level must remain below 0.5% alcohol by volume (ABV) during production and after shipment for commercial sale as a non-alcoholic refrigerated beverage. If at any time kombucha contains 0.5% or more alcohol, kombucha must be labeled with the health warning statement required by the Alcoholic Beverage Labeling Act of 1988 and is regulated as an alcoholic beverage. Kombucha products with less than 0.5% alcohol can continue to be marketed and sold as non-alcoholic beverages. However, if the product is packaged at an alcohol content less than 0.5% but the content increases to 0.5% or above prior to consumption, it also falls under TTB regulations. Control of factors, including temperature, acidity, glucose availability, and a complementary proportion of yeast and bacteria aid in limiting anaerobic alcohol production after packaging. A variety of approaches can be used to control the microbiologic activity. Kombucha can be pasteurized at 180°F (82°C) for 15 seconds in order to disable the fermentative yeasts and prevent them from producing more alcohol. If this technique is used to stabilize the kombucha, the brewer can subsequently dose known bacterial probiotics back into the beverage, if desired. Further, sterile filtration and microfiltration are also used to reduce the concentration of yeasts in the kombucha. Lastly, preservatives such as potassium sorbate and sodium benzoate can also be used to inhibit further fermentation.
Kombucha ingredients and ecological composition vary; therefore, individual reactions will differ and adverse health effects may occur. Although rare, there have been reported adverse effects of kombucha consumption that are unsubstantiated or related to poor hygiene or improper technique. The most common reported side effects from drinking kombucha include symptoms of allergic reactions, jaundice, nausea, vomiting, and head and neck pain, although these are also likely attributed to misuse of kombucha consumption or other pre-existing conditions. When kombucha is brewed in a home or in a commercial environment, there is a potential for the SCOBY to become contaminated with harmful organisms, including wild yeasts, bacteria, pests (i.e. fruit flies) and Aspergillus, a toxic mold. Even though the pH is kept relatively low, contamination can still occur so consumers must practice good hygiene, including keeping hands and all equipment clean and sanitary, using only food-safe fermentation vessels, and tightly covering the fermentation vessel by a clean fine-weave cloth to minimize air-borne contaminants while still allowing for air exchange.
As with trying any new food or beverage, consumers are advised to start with a small amount and observe one’s own results. New drinkers may experience temporary discomfort due to gut microbiome adjustments and, therefore, are recommended to drink no more than four ounces per day, with plenty of water, to minimize negative symptoms. The FDA states kombucha is safe for most individuals to consume up to four ounces per day. Consumption is not advised for individuals with compromised immune function, pregnant or lactating women, young children, or those with preexisting conditions, as possible health concerns are unknown. Isolated cases of gastrointestinal toxicity resolved after discontinuation of kombucha consumption, and daily kombucha consumption over two months was a suspected cause of lactic acidosis among two women in 1995, but a definitive causal link was not determined in any of these reported cases.
Many studies have explored the antimicrobial activity of kombucha. When the final pH is around 2.5, kombucha has antimicrobial activity across a broad spectrum of Gram negative and Gram positive bacteria and yeasts. However, the low pH of kombucha may not be the only reason for the antimicrobial activity; the natural polyphenols of tea, bacteriocins, as well as protein structures may also play a role in kombucha’s antimicrobial nature.
U.S. commercial sales of kombucha started with one company in 1995 and have grown steadily since. Within recent years, the increased interest and public recognition of probiotics, or live microorganisms that confer an investigated health benefit on the host, has driven growth in kombucha consumption. According to the SPINS Market Research Group, kombucha consumption experienced a 22% growth from February 2018 – February 2019, with yearly sales at $728.8 million. While kombucha originally began as a product mostly sold in health food stores, its rise in popularity has helped bottles make their way onto large chain-store shelves. Kombucha is the fastest-growing product in the functional beverage category. Kombucha Brewers International, the non-profit organization representing commercial kombucha brewers, strives for producers to work collaboratively, not just competitively. As an industry, their hope is to work together to maintain innovation, growth, and high product standards while advancing education and research.
A new category of kombuchas began to emerge around 2016, known as alcoholic kombucha or hard kombucha. These are kombuchas that are purposefully produced to have higher alcohol contents, typically between 4.5% ABV to 6.0% ABV. These kombuchas can be used as an alternative to beer, wine, cider, or spirits. This is a growing space, with new brands available as recently as 2020.
In most cases, kombucha contains live beneficial bacteria and yeasts, organic acids, B vitamins, antioxidants, and trace minerals. Unflavored kombucha contains generally about 30 calories, 2-3 grams of sugar, and small amounts of caffeine per eight ounces. Unflavored kombucha does not contain fat or cholesterol and is very low in protein and sodium. Added juice or flavoring ingredients may contribute additional micronutrients and will cause variation in caloric and macronutrient content as well. Additionally, varying amounts of alcohol (from <0.5% ABV up to 3.0% ABV) can be in kombucha, so consumers are advised to read the label carefully if alcohol-free beverages are required.
Kombucha has traditionally been consumed for its supposed health benefits, although many of the claimed health benefits from kombucha have not been adequately researched. Initially, it was believed to be a detoxifying agent, to aid in gastrointestinal health, and to have energizing properties. Consumers still consume the beverage for these perceived benefits, as well as many others, including its supposed influence on immunity, obesity, cardiovascular disease, atherosclerosis, hypertension, anemia, pulmonary disease, antioxidant capabilities, and cancer prevention. These claimed benefits, as well as many others, are being evaluated to determine if there is a relationship between consumption of kombucha and improved health and what the responsible mechanism may be. Results from animal studies link the majority of kombucha’s proposed health benefits to kombucha’s antioxidant properties and free radical scavenging ability, but lack confirmation in human trials.
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Laura Bauer, PhD
Department of Food Science and Human Nutrition, Colorado State University
David Dekevich, MPH
Liaison, Florida Integrated Food Safety Center of Excellence Florida Department of Health
Kristina Underthun, MS
University of Florida
Externally Reviewed by: Lauren Sandell Colorado Integrated Food Safety Center of Excellence, Colorado School of Public Health Reviewed on: 1 February 2021