The Hidden Partnership Behind Kombucha

There’s a disgusting, symbiotic secret behind the mouth-puckering fermented drink.

For anyone who’s never set foot in a Whole Foods, kombucha is a new “health drink” that’s experienced a near-meteoric rise in popularity over the last decade. Made from fermented black or green tea, kombucha is very slightly alcoholic (usually around 0.5% alcohol by volume, compared to beer’s 5% and wine’s 12%), lightly effervescent, and often sweetened with varying levels of sugar to offset its extremely sour taste.

Kombucha used to be a drink solely for New Age hippies, but companies like Kevita, Humm, GT, Brew Doctor, and others have recently brought it into the mainstream. Some companies market it as the next hit drink, while others emphasize that it may have minor health benefits (discussed below).

Even putting aside any health benefits, however, kombucha is still a tasty drink to many people. It’s also considered to be easier to prepare, in comparison to other fermented drinks such as wine or beer. Plenty of online kits and guides exist for brewing kombucha, even on Medium.

Most of the ingredients are straightforward — sugar, brewed tea, unchlorinated water, and jars to hold the product.

But there’s one more ingredient, with a weird-sounding name: SCOBY.

SCOBY, the Parents of All Kombucha

SCOBY is an acronym, standing for “Symbiotic Culture Of Bacteria and Yeast”. The term was invented specifically for kombucha in the 1990s; previously, this symbiotic culture was also referred to, confusingly, as kombucha.

More specifically, SCOBY is made up of bacteria in the Acetobacter genus, and Saccharomyces yeast. It sometimes (but not always) also contains other types of bacteria, like Lactobacillus and Pediococcus, and sometimes has other yeast species as well.

Just like how grape juice is transformed into wine through the actions of yeast, this mixture of bacteria and yeast eat the sugar and black or green tea that’s used as the starter for kombucha, transforming it into a combination of acid and other components that give the drink its sour, fruity tang.

Unlike in beer or wine, however, where the yeast sinks to the bottom as sediment, SCOBY forms a thick, rubbery mat in the fermenting vessel. The bacteria produce a mat of cellulose, which serves as a raft where the bacteria and their yeast buddies can grow and reproduce.

This rubbery mat can be off-putting in appearance, which is why it’s usually skimmed off the kombucha before consumption. Still, if you’ve ever tried the drink and found a thin bit of goopy film in the bottle, you’ve discovered a small amount of regrown SCOBY!

Just like in sourdough bread, SCOBY can be kept as a “mother mix” that is re-used for producing batch after batch of kombucha. Specific strains of bacteria or yeast in the SCOBY may add unique flavor profiles to the drink. Most home-brewed kombucha starts with a SCOBY packet purchased off Amazon for about $10, but some brewers keep their own SCOBYs growing for batch after batch.

Although the SCOBY term is generally used to refer to kombucha, the more general description — a biofilm — is a common term in microbiology. Biofilms form on almost every surface, including the counter of a kitchen, the inner lining of our large intestine, and even on our teeth! Ever rubbed your teeth and felt a kind of slime on them, perhaps after forgetting to brush? That’s a biofilm — a collection of bacteria that form a living mat that covers any available surface.

Bacteria and yeast are able to live together in a SCOBY thanks to a preference for complementary foods. Yeast, in an anaerobic (oxygen-free) environment, convert sugar into alcohol. Bacteria, in an oxygen-rich environment, take that alcohol and convert it into acetate, another organic molecule. By living together, with the bacteria on the oxygen-exposed surface of the SCOBY and with the yeast hidden in the oxygen-free interior, the two different organisms can feed off each other and support each other in a mutually beneficial, or symbiotic, relationship.

Kombucha may not be quite as widespread as beer, or have the same snobby culture built up around it as wine does — but unlike those two fermented drinks, it takes two different organisms working in a symbiotic partnership to produce each sip of kombucha.

What About Those Health Benefits of Kombucha?

Proponents of regular kombucha consumption claim that it contributes to a whole host of health benefits, including:

• a source of probiotic lactic-acid bacteria;
• contains similar compounds to green tea, which has its own range of health claims;
• a source of antioxidants;
• a high acetic acid content, which may act as an antibiotic against some potentially pathogenic bacterial species;
• potentially lowering low-density lipoprotein (LDL) levels, the “bad” cholesterol often connected to heart attacks;
• slowing the digestion of carbs, which may help prevent insulin spikes in diabetics;
• containing B vitamins and other compounds.

An online search will turn up all sorts of additional pronouncements, suggesting that kombucha may be the “miracle cure” that can help prevent or manage serious heart conditions or cancer. There’s practically no evidence to support these, and kombucha shouldn’t be considered a replacement for regular doctor’s visits, a balanced diet, and consistent exercise.

Still, if you’re used to gulping down a sugary soda, kombucha may be a slightly healthier choice. Next time you open a bottle or can, take a moment to appreciate the symbiotic partnership between creatures of two entirely different kingdoms — bacteria and yeast — that worked together to create this beverage for you.

Assuming you can handle the sourness, of course.

Sam Westreich holds his PhD in genetics, focusing on methods for studying the gut-associated microbiome. He currently works at a bioinformatics-focused startup in Silicon Valley. Follow on Medium, or on Twitter at @swestreich.

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