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Fermenting Kombucha

History

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Kombucha is a traditional fermented tea beverage. The tea used is from the Camellia sinensis plant and usually refers to black tea, although green tea is also used. Kombucha has gained great popularity due to the health benefits associated with it however, many of these benefits still remain unproven.[1][2]

The fermented tea is most commonly consumed in China, Russia, and Germany for many years[3]. A consensus on the exact geographic origin of Kombucha has not been reached but it is suggested that Kombucha tea originated in far east Asia several thousand of years ago.[1] Some suggest Kombucha originated in northeast China (Manchuria)[4]. There are reports of its consumption in Russia in the 1900s and spread to Europe.[4]

It is possible that the name “Kombucha” originates from Japanese words “kombu”, which means seaweed and “cha" which stands for tea although other theories have been proposed.[5]

Ingredients and Properties

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SCOBY (Symbiotic Culture of Bacteria and Yeast)

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SCOBY culture

In Kombucha, bacteria and yeast (tea fungus) work together to block the growth of potential contaminating bacteria and support fermentation. The culture is called the symbiotic culture of bacteria and yeast (SCOBY). The culture has a rubbery gel-like texture due to the formation of cellulose pellicles[6].There are several species of bacteria found but the main acetic acid bacteria in tea fungus are Gluconacetobacter xylinum, A. xylinoides, Bacterium gluconicum, A. aceti, A. pasteurianus. Gluconacetobacter xylinus is the most basic bacterium to exist in Kombucha[7][8]. Its role is to enhance the bond formed between bacteria and yeast, allowing the fermentation of the alcohols produced by the yeasts and facilitate acetic acid production by the bacteria. Acetic acid and ethanol are responsible for the antimicrobial effect against pathogenic microorganisms. They inhibit and destroy numerous gram-positive and gram-negative microorganisms[9].

Kombucha cultures may contain various yeasts, the typical yeasts found are: Schizosaccharomyces pombe, Saccharomycodes ludwigii, Kloeckera apiculata,Saccharomyces cerevisiae, Zygosaccharomyces bailii, Brettanomyces bruxellensis, B. lambicus, B. custersii, Candida and Pichia species[7][8]. In North American Kombucha, Zygosaccharomyces and S. cerevisiae were found to be the typical yeasts. These yeast cells are involved in metabolic activities with bacteria through the help of substrates.

Chemical structure of acetic acid

Acetic Acid

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The acetic acid is produced by bacteria (Acetobacter strains)[10]. During fermentation, the organic acids produced will decrease the pH value of Kombucha as fermentation time increases, making the beverage more acidic. Optimal fermentation time is required for a drinkable beverage because longer fermentation results in too high levels of acidity which may be harmful when consumed. Increased fermentation time will also increase antimicrobial activity due to the increase acid levels[10].

Other important chemical acid metabolites as a result of fermentation found in Kombucha are: acetic, lactic, malic, citric, oxalic, gluconic and glucuronic acids[9]. These organic acids help protect the symbiotic colony from contamination.

Tea

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Since Kombucha is made from tea, tea polyphenols are present, giving the tea a bitter, pungent and sweet aftertaste. Green and black tea have high catechin content. Green tea also contains caffeine[11]. Catechin and caffeine content will depend on brewing times and temperature. Longer brewing and hotter temperature have shown to increase catechin and caffeine[11].

Sucrose

Sucrose

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Sucrose is a disaccharide made up of two monosaccharides - glucose and fructose[12]. Sucrose is the major carbon source for the yeast. Sucrose is further hydrolyzed into its two monosaccharide components by the yeast.[13]

Production Process

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Tea leaves

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Black Tea Leaves (Oolong)

Tea leaves are picked from evergreen shrubs which can then be processed by different methods[7]. The tea leaves are first dried with or without nitrogen fixation to inactivate the enzymes[7] that contribute to the deteriorating process. Kombucha can be made from green or black tea leaves; however, black tea leaves are known to be the finest[14] and most commonly used. Black tea goes through an additional processing stage. Black tea leaves result from a multi-stage enzymatic process where the polyphenols are oxidized in the leaves. The enzymatic reaction yields new polyphenols which are formed during the oxidation processing of black tea. The reaction also contributes to darken leaves and stronger taste.

Standard Preparation of Tea

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Kombucha is commonly prepared in large glass jars, porcelain or glazed pottery[5] with a sealable lid. 5 g of tea leaves are added to 1L of boiling water and let to steep for ten minutes. The tea leaves are filtered and removed from the tea solution. 50 g of sucrose is dissolved in the hot tea and left to cool. 50 g of sucrose provides the optimal production of ethanol and acetic acid. A wide-mouthed clean container is used to hold the tea. 0.2 L of vinegar or previously made Kombucha is added to the tea to acidify the tea. This step is crucial for lowering the pH of the tea to inhibit the growth of undesirable microorganisms[9]. Tea fungus is placed on the tea surface. The container is covered with a clean cloth and fastened to additionally prevent undesirable insects such as Drosophila fruit flies away[7].

Culture Development

Fermentation and Culture Development

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The overall preparation of the tea drink is incubated at room temperature between 20°C and 30°C for 1-8 weeks[7]. Specific conditions must be in place for optimal fermentation by the bacteria to occur. The optimal temperature range is 18°C to 26°C[5]. This optimal temperature may be different around the world.

After a span of 2-3 days, a daughter tea fungus is formed at the surface of the tea. The daughter culture floats above the mother tea fungus previously placed in the tea. The mother fungus which is the starter culture initiates the fermentation process which produces the daughter culture. The daughter culture forms a clear thin gel-like membrane across available surface. This daughter culture creates a seal around the opening of the jar to protect the tea from the external environment. The old mother culture will remain in its original size and sinks to the bottom of the tea. The tea will start to smell fermented and gas bubbles appear in the form of carbonic acid[9]. The carbonic acid gives Kombucha it's distinct soda-like characteristic.[9]

Flavour Development

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The flavour depends on the amount of time the tea fungus is allowed to ferment in the tea. The longer the fermentation process will result in more acid production in the Kombucha. The taste can change from a fruit-sour-like sparkling flavour after a few days to a mild-vinegar-like taste[9] with prolonged incubation.

After Fermentation

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After 10-14 days, a new tea fungus is developed on the surface of the tea as a disc of 2 cm thick covering the entire diameter of the container[7].The tea fungus is removed from the developed tea and kept in a small volume of fermented tea for later use. The daughter fungus or SCOBY can be reused and acts as the mother culture for a new brewing. The beverage is passed through a cheese cloth.

Storage

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Kombucha stored in glass containers

Kombucha is best stored in the fridge so the fermentation process is slowed. Glass material is essential for decreasing the risk of the corrosion and leaching of toxic elements into the beverage[7]. Metal containers are not used as the acid will react chemically with metal. The result is an unfavourable taste. Plastic containers are growing increasing popular. Plastic containers must be high quality food grade and must be acid-resisting. Cheaper quality plastics may react with the acid and pose dangerous health concerns.[5] The SCOBY can also be dehydrated for prolonged discontinued use.

The SCOBY can be stored either in the fridge or at room temperature immersed in Kombucha. When kept at room temperature, the SCOBY requires more care (addition of more tea and/or sugar) because it is more active at its optimal room temperature. Avoid keeping the SCOBY in direct sunlight. It is best to store Kombucha with or without the SCOBY in a glass container (plastic or ceramic would work too) with a breathable lid[15].

Food Standards and Regulations in Canada

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Tea Regulations

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There are no specific regulations for Kombucha in Canada, but there are identity requirements for tea. Tea shall be the dried leaves and buds of Thea sinensis (L.) prepared by the usual trade processes. Black tea shall be black tea or a blend of two or more black teas and shall contain, on the dry basis, no less than 30% water-soluble extractive, no less than 4% and no more than 7% total ash. Green tea shall contain, on the dry basis, no less than 33% water-soluble extractive, no less than 4% and no more than 7% total ash.[16]

Alcohol Regulations

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If Kombucha (or any beverage) exceeds 1.1% alcohol by volume it is considered an alcoholic beverage by Canadian regulations. [17]

Health Claims

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Kombucha must also be subjected if a health claim, function claim or therapeutic claim is made. Health claims made in respect of probiotic microorganisms in food should be scientifically validated. Subsection 5(1) of the Food and Drugs Act states: "No person shall label, package, treat, process, sell or advertise any food in a manner that is false, misleading or deceptive or is likely to create an erroneous impression regarding its character, value, quantity, composition, merit or safety."[18]

Labelling

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In Canada, Kombucha is a food product that requires a label by the Consumer Packaging and Labelling Act and Regulations. Label requirements include common name, net quantity, name and address of the person responsible, ingredients list, nutrition facts table, durable life date (if storage life is 90 days or less), storage instructions, and bilingual labelling[19]. Labelling requirements are found in the 2003 Guide to Food Labelling and Advertising at the CFIA website: http://www.inspection.gc.ca/english/fssa/labeti/guide/ch2e.shtml[19]

Alcohol Labelling

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During the fermentation of the bacteria and yeast, Kombucha is usually produced with an alcohol content of 0-0.5%[13]. When fermentation time increases, the alcohol content may be more than 0.5%. If it is more than 1.1%, the Kombucha needs to follow alcohol labelling requirements [17].

Probiotic Labelling

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In Canada, proper labelling is also required for foods containing probiotic microorganisms. These requirements are found in the 2009 Canada's Guidance Document for The Use of Probiotic Microorganisms at the Health Canada website: http://www.hc-sc.gc.ca/fn-an/legislation/guide-ld/probiotics_guidance-orientation_probiotiques-eng.php[18]

The labelling of foods for which health claims about probiotics are made are required to follow:

  1. The term “probiotic(s)” and similar terms or representations should be followed by a statement that demonstrates the effects of the probiotic[20]
  2. The claimed effect of the probiotic microorganism in a food should be clearly stated in a way that is not false, misleading, deceptive, or likely to create an incorrect impression or assumption in regards to the effect of or benefit from the probiotic microorganism(s) in the food[20]
  3. When a health claim is made, it is require to declare the Latin name (i.e., genus and species) and the strain of the probiotic microorganism or mixed culture that is the subject of the claim[20]
  4. The level of the probiotic strain expressed in colony forming units (cfu) in a serving of stated size of the food should be declared[20]
  5. If more than one probiotic strain is added to a food, the reccomendations stated above apply to the mixed culture. [20]

Nutrition

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There are many health claims associated with protection against cancer[7], prevention of cardiovascular diseases[7], reduce stress, prevent bladder infections and many more. The available studies are limited and are performed in vitro and on rat subjects[7][2][21][22]. The available evidence is not recommended to be generalized to the public as human health benefits as there is no strong evidence to support such health claims.

However, studies[23][24] have shown that the intake of fermented teas has more superior nutritive and therapeutic value when compared to non-fermented tea.

Vitamins

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Black tea fermentation results in accumulation of major vitamins such as A, B1, B2, B12 and C. With daily intake of Kombucha, the tea provides the recommended daily allowances of these vitamins.[23]Daily intake also provides more Vitamin C than black tea[23].

Antioxidant source

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Antioxidant compounds such as polyphenols and catechin are present in high amounts in tea leaves[11]. Epigallocatechin gallate (EGCG)[11] is the primary catechin in tea that inhibits free radical oxidation reactions which lead to harmful chain reactions in the body.

Probiotic and Prebiotic Benefits

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Kombucha contains a combination of prebiotics and probiotics[9]. Prebiotics help the growth and activity of beneficial microbes in the human gut. Probiotics which are present as bacteria and yeast in the drink facilitate the growth of the beneficial microbes in the intestine. Probiotic microorganisms normalize the gut flora and boost the immune system.[9]

Controversies

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There has been many claims about the health benefits of Kombucha, including improved gastrointestinal health, increased energy, strengthened immune system, and enhanced appearance of skin and hair. Kombucha has been said to decrease risks of cancer. [25][26]However, these claims have not been scientifically proven.

Some say that home-brewing Kombucha can have potential dangers if harmful microorganisms are in the broth [25][27]. Others believe that when Kombucha is exposed to mold, there should be no significant effects[28].

There has been many false claims about Kombucha containing usnic acid and glucurinic acid, but no testing has shown that it does. Some say that it is best to limit consumption to half a cup 2-3 times a day for the normal adult to avoid consuming too much of acid. [26] There has also been beliefs that Kombucha can cause a build up of lactic acid and can be dangerous [25]

Kombucha has the potential to become an alcoholic beverage as it continues to ferment. There has been some controversy about selling Kombucha because of its potential of becoming alcoholic beverage. Some brands are now off the market due to the small alcoholic content [29]


  1. ^ a b Teoh, Ai Leng; Heard, Gillian; Cox, Julian (2004-09-01). "Yeast ecology of Kombucha fermentation". International Journal of Food Microbiology. 95 (2): 119–126. doi:10.1016/j.ijfoodmicro.2003.12.020.
  2. ^ a b Ahangar Da, Mahboobeh; Kabiri, Najmeh; Rafieian-K, Mahmoud; Setorki, Mahbubeh; Doudi, Monir. "Protective Effect of Kombucha Tea on Liver Damage Induced by Thioacetamide in Rats". Journal of Biological Sciences. 14 (5): 343–348. doi:10.3923/jbs.2014.343.348.
  3. ^ Chu, Sheng-Che; Chen, Chinshuh (2006-01-01). "Effects of origins and fermentation time on the antioxidant activities of kombucha". Food Chemistry. 98 (3): 502–507. doi:10.1016/j.foodchem.2005.05.080.
  4. ^ a b Sreeramulu, Guttapadu; Zhu, Yang; Knol, Wieger (2000-05-17). "Kombucha Fermentation and Its Antimicrobial Activity". Journal of Agricultural and Food Chemistry. 48 (6): 2589–2594. doi:10.1021/jf991333m.
  5. ^ a b c d Tietze, Harald (1996). Kombucha: The miracle fungus. New South Wales: PHREE Books. ISBN 0-646-23106-5.
  6. ^ Kallel, Lina; Desseaux, Véronique; Hamdi, Moktar; Stocker, Pierre; Ajandouz, El Hassan (2012-11-01). "Insights into the fermentation biochemistry of Kombucha teas and potential impacts of Kombucha drinking on starch digestion". Food Research International. 49 (1): 226–232. doi:10.1016/j.foodres.2012.08.018.
  7. ^ a b c d e f g h i j k Dufresne, C.; Farnworth, E. (2000-07-01). "Tea, Kombucha, and health: a review". Food Research International. 33 (6): 409–421. doi:10.1016/S0963-9969(00)00067-3.
  8. ^ a b Battikh, Houda; Bakhrouf, Amina; Ammar, Emna (2012-06-01). "Antimicrobial effect of Kombucha analogues". LWT - Food Science and Technology. 47 (1): 71–77. doi:10.1016/j.lwt.2011.12.033.
  9. ^ a b c d e f g h Watawana, Mindani I.; Jayawardena, Nilakshi; Gunawardhana, Chaminie B.; Waisundara, Viduranga Y. (2015-12-30). "Health, Wellness, and Safety Aspects of the Consumption of Kombucha". Journal of Chemistry. 2015: 1–11. doi:10.1155/2015/591869.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  10. ^ a b Sreeramulu, Guttapadu; Zhu, Yang; Knol, Wieger (2000-05-17). "Kombucha Fermentation and Its Antimicrobial Activity". Journal of Agricultural and Food Chemistry. 48 (6): 2589–2594. doi:10.1021/jf991333m.
  11. ^ a b c d "PEN - Practice-based Evidence in Nutrition". PEN. Retrieved 2016-03-23.
  12. ^ "Sucrose - Oxford Reference". doi:10.1093/acref/9780199234875.001.0001/acref-9780199234875-e-5231. {{cite journal}}: Cite journal requires |journal= (help)
  13. ^ a b Lončar, E.; Djurić, M.; Malbaša, R.; Kolarov, L.J.; Klašnja, M. "Influence of Working Conditions Upon Kombucha Conducted Fermentation of Black Tea". Food and Bioproducts Processing. 84 (3): 186–192. doi:10.1205/fbp.04306.
  14. ^ Jayabalan, Rasu; Malbaša, Radomir V.; Lončar, Eva S.; Vitas, Jasmina S.; Sathishkumar, Muthuswamy (2014-07-01). "A Review on Kombucha Tea—Microbiology, Composition, Fermentation, Beneficial Effects, Toxicity, and Tea Fungus". Comprehensive Reviews in Food Science and Food Safety. 13 (4): 538–550. doi:10.1111/1541-4337.12073. ISSN 1541-4337.
  15. ^ "Kombucha Frequently Asked Questions | Kombucha FAQ". www.culturesforhealth.com. Retrieved 2016-03-23.
  16. ^ Branch, Legislative Services. "Consolidated federal laws of canada, Food and Drug Regulations". laws.justice.gc.ca. Retrieved 2016-03-14.
  17. ^ a b Directorate, Government of Canada,Canadian Food Inspection Agency,Food Labelling and Claims. "Labelling Requirements for Alcoholic Beverages". www.inspection.gc.ca. Retrieved 2016-03-14.{{cite web}}: CS1 maint: multiple names: authors list (link)
  18. ^ a b Branch, Government of Canada, Health Canada, Health Products and Food. "Guidance Document: The Use of Probiotic Microorganisms in Food [Health Canada, 2009]". www.hc-sc.gc.ca. Retrieved 2016-03-17.{{cite web}}: CS1 maint: multiple names: authors list (link)
  19. ^ a b Agency, Government of Canada,Canadian Food Inspection. "Food Labelling for Industry". www.inspection.gc.ca. Retrieved 2016-03-23.{{cite web}}: CS1 maint: multiple names: authors list (link)
  20. ^ a b c d e Branch, Government of Canada, Health Canada, Health Products and Food. "Guidance Document: The Use of Probiotic Microorganisms in Food [Health Canada, 2009]". www.hc-sc.gc.ca. Retrieved 2016-03-23.{{cite web}}: CS1 maint: multiple names: authors list (link)
  21. ^ Abshenas, Jalil; Derakhshanfar, Amin; Ferdosi, Mohammad Hosein; Hasanzadeh, Saeid (2011-06-22). "Protective effect of kombucha tea against acetaminophen-induced hepatotoxicity in mice: a biochemical and histopathological study". Comparative Clinical Pathology. 21 (6): 1243–1248. doi:10.1007/s00580-011-1273-9. ISSN 1618-5641.
  22. ^ Bellassoued, Khaled; Ghrab, Ferdaws; Makni-Ayadi, Fatma; Pelt, Jos Van; Elfeki, Abdelfattah; Ammar, Emna (2015-11-02). "Protective effect of kombucha on rats fed a hypercholesterolemic diet is mediated by its antioxidant activity". Pharmaceutical Biology. 53 (11): 1699–1709. doi:10.3109/13880209.2014.1001408. ISSN 1388-0209.
  23. ^ a b c Pasha, Chand; Reddy, Gopal (2005-02-01). "Nutritional and medicinal improvement of black tea by yeast fermentation". Food Chemistry. 89 (3): 449–453. doi:10.1016/j.foodchem.2004.02.054.
  24. ^ Vīna, Ilmāra; Semjonovs, Pāvels; Linde, Raimonds; Deniņa, Ilze (2013-11-05). "Current Evidence on Physiological Activity and Expected Health Effects of Kombucha Fermented Beverage". Journal of Medicinal Food. 17 (2): 179–188. doi:10.1089/jmf.2013.0031. ISSN 1096-620X.
  25. ^ a b c "Kombucha is steeped in controversy". tribunedigital-baltimoresun. Retrieved 2016-03-23.
  26. ^ a b "Kombucha Tea | American Nutrition Association". americannutritionassociation.org. Retrieved 2016-03-23.
  27. ^ "How Healthy Is Kombucha, Really?". The Huffington Post. Retrieved 2016-03-23.
  28. ^ "Kombucha, kefir and Probiotic fermenting Cautions, Advice and Tips for a safe and healthy fermen". www.happyherbalist.com. Retrieved 2016-03-23. {{cite web}}: line feed character in |title= at position 74 (help)
  29. ^ "Kombucha Controversy: Is the Government Killing a Super-Healthy Drink Market?". www.cbsnews.com. Retrieved 2016-03-23.
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