Course:FNH200/2015w Team06 Kombucha
1. Background Kombucha tea is a traditional non-alcoholic fermented beverage originated in the Orient. The tea leaves used is from the Camellia sinensis plant and usually refers to black tea although green tea is sometimes used. It is possible that the name “Kombucha” originates from Japanese words “kombu" and "cha" which mean seaweed and tea respectively. However, other theories have been proposed. 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. There are reports of its consumption in China that date back to 220 BC. It is suggested it entered Japan from Korea in 414 AD and east Russia in the 1900s, expanding to Europe from there.
2. Ingredients/Composition & Properties
Bacteria
In Kombucha, bacteria and yeast (tea fungus) work together to block the growth of potential contaminating bacteria and support fermentation. Thus, the common name for symbiotic culture of bacteria and yeast (SCOBY) is Kombucha. 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, and A. pasteurianus.
Gluconacetobacter xylinus is the most basic bacterium to exist in Kombucha. Its role is to enhance the bond formed between bacteria and yeast, allowing the fermentation of the alcohols produced by the yeasts to be converted to acetic acid. Acetic acid is responsible for the antimicrobial effect against pathogenic microorganisms, it inhibits and destroys numerous gram-positive and gram-negative microorganisms.
Yeast
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. 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. Yeast cells prefer fructose as a substrate to hydrolyze sucrose into glucose and fructose (by invertase), and produce ethanol (through glycolysis). The acetic acid produced by bacteria (Acetobacter strains), metabolizes glucose to gluconic acid and ethanol is oxidized to acetic acid. 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.
Important chemical metabolites found in Kombucha are: acetic, lactic, gluconic and glucuronic acids, ethanol and glycerol. These organic acids help protect the symbiotic colony from contamination. The fermentation process is reported to promote the synthesis of the vitamin B complex and folic acid. Vitamins B1, B2, B6, B12, and C are present. Since Kombucha is made from tea, tea polyphenols are also present, giving the tea a bitter, pungent and sweet aftertaste. The concentration and composition of the metabolites varies according to the tea fungus, amount of sugar, and fermentation time. The main components found in kombucha tea at the end of fermentation on sugared black tea infusion are: acetic acid, glucuronic acid, gluconic acid, glucose, fructose, and sucrose.
3. Production Process
Tea leaves Tea leaves are picked from evergreen shrubs which can then be processed by different methods. The tea leaves are first dried with or without nitrogen fixation to inactivate enzymes. This process slows down the rate of leaves from deteriorating. Depending on the whether the tea leaves are made into green or black tea leaves, black tea leaves go 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.
Preparation of Tea - standard preparation
[1]Kombucha is commonly prepared in large glass jars with sealable lids. Glass material is essential for decreasing the risk of the corrosion and also provides a way to monitor the growth of the tea fungus. Bring 1.5L of water and ½ cup organic cane sugar to a boil and then remove from heat and add 2-4tbsp of loose leaf tea (or 3-4 teabags) to the water. Let steep 20min depending on how strong you want the flavour. Strain tea leaves and leave tea mixture to cool to room temperature. Once the tea is at room temperature, pour into a wide mouthed glass jar with the SCOBY body and your starter tea (from the last batch) and cover with a cheese cloth or tea towel and leave to ferment. Taste every few days- usually between 7-30 days for initial fermentation period.
Once the Kombucha is to your desired taste, remove the SCOBY body and disperse tea into sealable glass jars. Add flavour if desired and seal, allowing flavour to ferment for 3-7days and then move the tea to your fridge. Serve cold.
Fermentation and Culture Development
The preparation is incubated at room temperature between 20°C and 30°C for 1-8 weeks.
Optimal temperature range is 18°C to 26°C A daughter tea fungus is formed at the tea surface within a span of 2-3 days. Daughter culture floats above the old mother tea fungus and forms a clear thin gel-like membrane across available surface. Tea will start to smell fermented and gas bubbles appear in the form of carbonic acid. The old mother culture will remain in its original size and sinks to the bottom of the tea
Flavour Development The flavour depends on the amount of time the tea fungus is allowed to ferment in the tea. The longer the fermentation process, the more acidic the Kombucha. The taste can change from a fruit-sour-like sparking flavour after a few days to a mild-vinegar-like taste with prolonged incubation.
After Fermentation 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.
The tea fungus is removed from the developed tea and kept in a small volume of fermented tea for later use
Beverage is passed through a cheese cloth and stored at 4°C