Do I have to say more? I think we've all had kombucha at some point, and it's one of the most well-known and popular fermented beverages. You can make it any flavor you want, it's supposedly very healthy and naturally carbonated. What more could you ask for from a drink? Kombucha is traditionally made from fermented black tea, but almost any liquid with enough sugar can be fermented into kombucha. For example, to increase the health benefits, some researchers and food scientists add Jerusalem artichoke tuber extract to produce the same metabolites as sucrose fermentation, with added inulin (prebiotic fiber) and fructooligosaccharides, a fermentable oligosaccharide (multiple sugar chains) that has been shown to be beneficial for gut microbiota. Kombucha is an example of cooperative fermentation using a SCOBY (symbiotic colony of bacteria and yeast), which as a collection of microbes first convert sugar into alcohol, then into acetic acid (HC2H3O2). The specific variations of microbes vary, but the most common organisms are yeasts, unicellular fungi, and acetic acid bacteria (AAB). The yeast present is often saccharomyces cerevisiae, but the SCOBY can include many of its relatives. Often several strains of AAB might be present, but some variation of Gluconacetobacter or Acetobacter will usually be present: however, according to an analysis of the metabolic byproducts of kombucha, the main acids present are acetic, gluconic, tartaric, malic and citric acid. The relationship between AAB and yeast can be described as commensalism: the bacteria benefit more from the yeast, but saccharomyces tolerates acidic environments and is not significantly affected. But how is the SCOBY created and why is it solid?The bacteria and yeast live on a structure called a zoogleal mat: as they multiply and propagate, they excrete cellulose, forming a sheet that floats on the liquid. As the mixture ferments, the mat grows, spreading to the edges and then increasing in thickness, creating the solid formation that appears on the surface of kombucha. Living on the mat allows the AAB to be in direct contact with the air above the liquid needed to undergo alcohol fermentation, which also allows the bacteria to metabolize and create a stronger cellulose network. Once introduced to a sugary liquid, the yeast in SCOBY begins fermenting by consuming simple sugars and producing alcohol and CO2 as a byproduct. The AAB then ferment the ethanol by oxidizing it into acetic acid, using the oxygen available in the environment. According to The Noma Guide to Fermentation, “As a rough guide, under ideal conditions, yeast typically ferments 2 units of sugar into 1 unit of alcohol, and AAB converts 1 unit of alcohol into just under 1 unit of acetic acid”. Vinegar is made in a similar process with one distinction: vinegar is a 2 stage fermentation. First, yeast converts sugar to alcohol, and some strains have different tolerance for alcohol and will die off once that level is met or they are killed by pasteurization. In the second stage, AAB ferments alcohol into acid, but without the yeast, bacteria will eventually run out of fuel and the fermentation will stop. In contrast, Kombucha is a sustained fermentation: yeast continually ferments sugar into ethanol for the bacteria to convert into acetic acid, so the beverage will continually become more and more sour until all available sugar is consumed. Thus, it is crucial to control when the kombucha is bottled, how it is stored and how quickly it is consumed so the ideal sweetness and acidity is achieved. SCOBY thrives in a slightly lower pH environment, with an optimum temperature in the range of 77 to 90˚F. In order to prevent wild fungal molds like Aspergillus, which can produce water-soluble toxins, you need to backslop with some kombucha from the first batch as with other ferments to establish an ecosystem. However, the sweetness is crucial in the making of kombucha, as too much can induce a higher production of acetic acid and alcohol than desired and too little will not produce enough sweetness or fermented flavor. Thus, the degrees Brix (Bx) measurement of the amount of dissolved sucrose as a percentage of the total solution is critical to calculate the ideal sweetness and fermentation of kombucha. The Brix measurement is calculated using the specific gravity of the solution: ratio of the density of a solution to the density of normal water. The higher the density of sugar, the higher the brix measurement. Degrees brix can be measured with a refractometer, which measures the way the solution refracts light as sucrose changes light refraction. Noma has determined for their restaurant that 12˚˚Bx is an ideal concentration of sugar for the desired sweetness and acidity, but it varies based on the desired result. Kombucha historically originates in Northeast China or Manchuria around 220 BC, and it was initially prized for healing properties. The name stems from Dr Kombu, a Korean physician who brought the drink from China to Japan as a cure for Emperor Inkyo (hence the name: cha = tea, kombu being the name of the doctor). Despite its decline during WWII because of a lack of tea and sugar, the beverage regained popularity in the 1960s due to a Swiss study showing health benefits comparable to yogurt. However, many attribute the widespread growth of kombucha's popularity to GT Dave, the brand that started in 1995. The fermentation movement during the 90s also helped the beverage gain national popularity, cementing it as a supermarket staple rather than just a niche drink. Kombucha production has had its ups and downs: regulatory issues arose in 2010 when it was discovered that during the second fermentation producers were not monitoring ABV levels in the bottles. Thus, the kombucha could be anywhere from 0.5% to 2.5% ABV (for context, some beers are 3.0%). It was withdrawn briefly from stores until the Alcohol and Tax Bureau established regulations for minors on higher than 0.5% beverages. Safe to say that many people drink kombucha and some dismiss its health claims because of the sugar content, but it's actually really good for you. Kombucha is considered a superfood, as one serving gives 20% of daily B vitamins and 25% of daily folic acid (B6). Research has demonstrated a clear antimicrobial activity against certain pathogens in the body, largely due to the presence of catechins and acetic acids. Phenolic compounds were also shown to increase over fermentation period in the kombucha, increasing the antioxidant profile of kombucha, which was already high due to tea polyphenols, ascorbic acid and DSL. Kombucha has even been shown to protect against hepatotoxicity induced by various pollutants. Tea fungus in particular, the biomass produced as a film on top of the kombucha has been shown to be extremely beneficial for health, as it is rich in crude fiber, protein, and amino acid lysine. There are claims that it is beneficial for gut microbiota, but those are yet to be proven: even so, it likely aids in establishing some good bacteria on the surface of the gut, so it may have some residual effect. Kombucha is obviously consumed as a beverage, but the SCOBY is also candied in the Philippines and eaten as a sweet called nata. The candy is often made from the cellulose byproduct of vinegar since they produce so much in the Philippines, but kombucha can be used in the same way. Kombucha can also be used to cook with as a seasoning, and its uses are varied in the pastry world, but the possibilities are broader than you might imagine. Noma uses kombucha as part of the beverage pairing for their meals to compliment the flavors of the dishes, and they add native ingredients like sea buckthorn and rose hips to reflect the Nordic climate. I won't tell you to try it because likely you've had kombucha already, but I encourage you to find more creative ways to use it. Use it in salad dressings, as part of braises, marinating liquids, cake soaks, really anything!
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May 2020
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