Kombucha tea continues to grow in popularity as a healthy alternative to alcoholic beverages—and chemistry can help commercial and amateur brewers alike get faster and better results with their brews, according to a presentation yesterday at a meeting of the American Chemical Society in New Orleans.
“Brewers typically see making kombucha as an art more than a science,” Jeb Kegerreis, a physical chemist at Shippensburg University, said of the research. “So when we are doing a consultation, we also walk the brewer through the biochemistry of what’s happening during fermentation.”
As we've previously reported, you need just three basic ingredients to make kombucha. Just combine tea and sugar with a kombucha culture known as a SCOBY (symbiotic culture of bacteria and yeast), aka the "mother," also known as a tea mushroom, tea fungus, or a Manchurian mushroom. It's basically akin to a sourdough starter. A SCOBY is a firm, gel-like collection of cellulose fiber (biofilm), courtesy of the active bacteria in the culture creating the perfect breeding ground for the yeast and bacteria to flourish. Dissolve the sugar in non-chlorinated boiling water, then steep some tea leaves of your choice in the hot sugar water before discarding them.
Once the tea cools, add the SCOBY and pour the whole thing into a sterilized beaker or jar. Then cover the beaker or jar with a paper towel or cheesecloth to keep out insects, let it sit for two to three weeks, and voila! You've got your own home-brewed kombucha. A new "daughter" SCOBY will be floating right at the top of the liquid (technically known in this form as a pellicle).
There are two kinds of fermentation taking place: alcoholic fermentation and acetic acid fermentation. A really good kombucha will strike the perfect balance between the two. The yeast in the SCOBY produces an enzyme (invertase) that breaks the sugar into fructose and glucose. The glucose then breaks down into pyruvate, acetaldehyde, and finally ethanol, releasing carbon dioxide as a byproduct to give kombucha that pleasing touch of carbonation.
It's not a lot of ethanol, since the bacteria in the SCOBY converts much of it into acetic acid. Too much alcohol would actually stop the fermentation process. So most kombucha teas have less alcohol than even a very light beer. You can get higher alcohol concentrations if you add too much sugar and/or let the stuff ferment too long, but then your kombucha will probably just taste like straight vinegar.
"I think as [kombucha] becomes a more popular beverage it can take the place of soda in somebody’s diet," Kegerreis said during a media briefing. "It has the carbonation, the fizz, and it doesn’t have nearly the same sugar content in grams per liter. Compared to soda, kombucha is a much healthier alternative. A lot of our research focuses on making sure that it maintains its status as a nonalcoholic beverage. So we focus a lot on keeping ethanol content below the legal limit for a non-alcoholic beverage."
There's still a lot of uncertainty in the fermentation process since the bacteria and yeast can vary with every batch. Kegerreis has been working with John Richardson, who founded Cultured Analysis, a consulting company within the university devoted to discovering new ways to optimize the brewing process for the benefit of both amateur and commercial kombucha producers. “Brewing kombucha can still be a very creative process,” said Richardson. “But when something goes wrong during fermentation, science can help make it right.”
Kegerreis and Richardson decided to take a closer look at the containers used for brewing, testing the viability of using silicone bags commonly used for sous vide cooking. Their interest stemmed from a tip by a fellow brewer, who reported that the bags seemed to brew kombucha faster and that the resulting brews had higher acid and lower alcohol content compared to tea brewed in the now-standard glass jars. But why?
Based on their own comparative experiments, Kegerreis and Richardson found that the difference was due to the silicone bag's porosity. This exposes the SCOBY to more oxygen, so ethanol breaks down faster, cutting brewing time in half (from two weeks to one). That said, the amount of dissolved oxygen in the bags was inconsistent. Figuring out why that's the case will be the focus of the next round of experiments.
Brewing kombucha in silicone bags also produced more acid, particularly gluconic acid. Furthermore, using glucose rather than sucrose as a food source for the bacteria essentially eliminates the traditional first step in the process, in which the sucrose breaks down into glucose and fructose. They found that using glucose alone produces more gluconic acid, while fructose alone produces more acetic acid and ethanol and makes the resulting tea taste sweeter. “We think [gluconic] acid will become more popular with brewers,” said Kegerreis. “Gluconic acid provides acidity without the sour vinegar taste you get from acetic acid, and that may appeal to more tastebuds.”
Beyond its popularity as a beverage, kombucha holds promise as a useful biomaterial. For instance, scientists at MIT and Imperial College London last year created new kinds of tough "living materials" out of SCOBYs that could one day be used as biosensors. These materials could help purify water or detect damage to "smart" packing materials. Any number of strains can be swapped out to achieve different functional properties. Other research showed that membranes grown from kombucha cultures were better at preventing the formation of biofilms—a significant challenge in water filtration—than current commercial membranes.
In 2021, Andrew Adamatzky of the University of the West of England in Bristol, UK, demonstrated that living kombucha mats showed dynamic electrical activity and stimulating responses. A 2022 paper described the development of a bacterial reactive glove to serve as a living electronic sensing device. And last year, Adamatzky demonstrated that it's possible to print electronic circuits onto dried SCOBY mats for potential wearable electronics.
