Oregon was home to one of the first kombucha brands in the United States and has since maintained its status as a leader in the $1.4 billion global industry. Local outfits such as Tualatin-based Brew Dr., Bend-based Humm and Portland’s Kombucha Wonder Drink are some of the top brands around.
Now researchers in the state are making their own mark on the kombucha landscape by starting to solve one of the mysteries surrounding the fizzy, vinegary, fermented tea: what exactly gives it its distinctive flavors?
“Compared to other fermentation systems … there’s much more variability in what can carry out the fermentation than say beer or wine, where it’s pretty much carried out by the same organism every time,” said Chris Curtin, a fermentation microbiologist at Oregon State University.
Beer and wine use specific yeasts to generate flavors and alcohol. The fermentation process for kombucha is more complex.
Kombucha is fermented using a SCOBY — a gelatinous mass of bacteria and yeast working in consort (the acronym stands for “symbiotic culture of bacteria and yeast”). The yeast in the SCOBY turns sugars in the sweet tea base into alcohol, and then the bacteria turn that alcohol into the acid that gives the vinegary flavor.
Curtin says it’s especially difficult to understand the relationship between flavor and SCOBY because very little has been known about what varieties of bacteria and yeast are present, and in what relative combinations.
“Because it’s involving multiple yeast and bacteria, it’s much harder to ... dial in,” he said. “How can we help the kombucha industry make a more consistent product? Where do we even start when we don’t have any idea what the typical SCOBY looks like?”
Curtin and other researchers at Oregon State are answering those questions.
They analyzed the DNA from 103 different SCOBYs provided by kombucha brewers from North America and beyond to figure out what kinds of bacteria and yeast were present. They found that each SCOBY could be grouped into one of four archetypal mixes.
The most common grouping of the SCOBYs tested is dominated by Brettanomyces yeast (commonly used to make sour and Belgian-style beers) and Komagataeibacter, an acetic acid bacteria used in vinegar production.
This counters previous work into the microbiome of SCOBYs that often concluded that another yeast (Zygosaccharomyces) was the most common. Curtin says their work benefited from a much larger number of SCOBYs analyzed.
Because there are several different species of each type of bacteria and yeast identified, more detailed information about which are present will likely be needed to fully understand the links between SCOBY composition and the resulting kombucha.
Curtin’s lab is currently working to make those connections.
“If we know which microbes are in different kombucha SCOBY types and what they do, then we can design new SCOBYs,” he said.