Using Vessel Geometry to Control the Alcohol Content of Kombucha

By Bill Nootenboom

President, Stout Tanks & Kettles

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Kombucha brewers have long struggled to keep the alcohol content of their kombucha low.  Federal law is clear:  If kombucha EVER exceeds 0.5% Alcohol By Volume (“ABV”), at any point in the production process, then all Alcohol and Tobacco Tax and Trade Bureau (“TTB”) regulations regarding alcoholic beverages apply.  Compliance can be costly and difficult. You must register with the TTB, get all of your recipes and labels approved, pay all applicable state and federal taxes, and comply with the rules about how your product can be stored, distributed and sold. The only way to avoid the taxes and regulations is to make sure the ABV is ALWAYS below 0.5%. Most Kombucha producers want to provide compliant products to provide peace of mind for their customers who are seeking low alcohol beverages to share with their family or those who do not consume alcohol.

Stout Tanks and Kettles has been working with Bare Bucha, a kombucha brewery in Waco, Texas that took the ABV challenge seriously. Toby Tull and David Aycock, the owners of Bare Bucha, conducted over 800 tests of different batches in prototype stainless steel fermenting vessels manufactured by Stout Tanks in order to figure out how to best produce legal, low-alcohol kombucha. The result:  The Symbiosis FermenterTM, a one-of-a-kind patent-pending kombucha brewing vessel that ferments faster, reduces alcohol content, and makes it easier to comply with federal laws.

Innovating The Symbiosis FermenterTM required a return to the fundamentals of fermentation. kombucha is fermented with a SCOBY, or a Symbiotic Culture of Bacteria and Yeast. Kombucha uses both yeast and bacteria to ferment the beverage. Yeast convert sugars into alcohol and carbon dioxide. The bacteria use oxygen to convert the  alcohol into organic acids, including acetic acid, lactic acid, and gluconic acid. David and Toby realized early on that creating a balanced symbiosis of bacteria and yeast was the key to using nature to keep alcohol levels under the legal limit, and provide healthy and flavorful kombucha, with all its probiotic benefits. 

When Toby Tull and David Aycock started Bare Bucha in Waco Texas, they were unapologetically pro-probiotic. They loved the health benefits that kombucha offered, full of healthy bacteria and organic acids. And they were also committed to following the rules, and creating a product that proudly complied with all rules. They wanted to use nature itself, and the symbiotic power of the community of microbes in kombucha.  They did not want to dilute their kombucha with water before bottling to meet the 0.5% ABV requirement. They did not want to rely on million dollar machines to remove the alcohol with an industrial distillation process. They also did not want to pasteurize their kombucha at any point in the process in order to kill the yeast before they could create more alcohol. Killing the yeast with pasteurization removes the very biotics that make kombucha probiotic.

In the course of over 800 tests, Bare Bucha found that fermentation in traditional cylindrical shaped fermenters favors the alcohol producing yeasts.  Cylindrical fermenters capture carbon dioxide from the yeast, which displaces the oxygen that bacteria need, thereby skewing the kombucha toward yeast and alcohol and away from oxygen and bacteria. Kombucha yeast includes largely Brettanomyces species, which are not typically present in beer, and are usually associated with off-flavors of wine. These yeasts start consuming sugars and creating alcohol long before the bacteria can get going. The shape of the traditional fermenter means that the bacteria are always behind the curve. Hundreds of fermentation tests in traditional fermenters show that the yeast start fermenting early, reducing sugars, and creating alcohol. The bacteria take much longer to start consuming alcohol and creating acetic acid.

When testing the Symbiosis Fermenter™, which features a unique shape, Bare Bucha found the bacteria were able to get ahead of the curve, and start consuming alcohol before it exceeded the legal limit, and creating more acetic acid sooner. The result was that they were able to reach their desired flavor profiles more quickly, with the same levels of organic acids as produced in a traditional fermenter, and also never exceed the legal limit for alcohol. Bare Bucha was able to achieve its desired flavor profile after only 14 days of fermentation in a Symbiosis FermenterTM.  In a traditional cylindrical fermenter, it takes over 40 days to get the alcohol levels and organic acid levels to the proper result. This allows Bare Bucha to use less sugar and less time to achieve the same flavor and probiotic result, and never exceed the current ABV limit.

The Symbiosis FermenterTM is a new shape of fermentation vessel engineered especially for kombucha.  The bacteria primarily responsible for consuming the alcohol are Komagataeibacter species, which require oxygen to metabolize alcohol and ferment best at the surface.. To directly accommodate this behavior, we created a shallow pan with an  open top creating a large surface area to give the Komagataeibacter bacteria access to oxygen so they can thrive. The bacteria perform best in temperatures above 80 degrees Fahrenheit, so we created a single walled pan that allows the kombucha to absorb heat from the surrounding air. Brewers can control the heat by increasing the ambient temperature of their fermentation room.

Stout Tanks is proud of this collaboration and are glad to be able to offer this significant step forward in commercial kombucha fermentation. It’s a big win for those who want to brew authentic, traditional, live and raw kombucha product we all love while maintaining low ABV without additional processing stepsFor more about The Symbiosis Fermenter™, please visit us online at or contact us directly at (503) 972-9580.

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