Three ways scientists are working to improve kombucha brewing

Many brewers can find it challenging to keep kombucha’s alcohol levels low because the bacteria and yeast used in the fermentation process vary from batch to batch.

Now chemists from Shippensburg University are investigating how to reliably minimise alcohol levels in kombucha, tailor taste profiles and speed up the fermentation processes to help producers optimise the production of the fermented tea.

Kombucha brewing typically begins with a glass jar filled with tea, water, sucrose and a fermentation starter called a SCOBY — short for a symbiotic culture of bacteria and yeast.

The research, presented at the spring meeting of the American Chemical Society, investigated the use of silicone bags as an alternative to glass jars for brewing kombucha. It found that a silicone bag’s porosity, compared to a glass jar, exposes the SCOBY to more oxygen, which speeds up the brewing process — including ethanol breakdown and acid production — cutting production time from about two weeks to one week.

However, the researchers found that there were inconsistent levels of dissolved oxygen in the silicone bags compared to the glass jars so further research is needed to discover the full reason why the silicone bag is a better brewing vessel for reducing ethanol.

In a glass jar, a kombucha pellicle — the rubbery puck of cellulose that holds most of the bacteria and yeast culture — forms at the surface (top). With the silicone bags, however, the researchers noticed that the pellicle formed all the way around the inside (bottom). The increased surface area of the culture in the silicone bag may be one of the factors that speeds fermentation compared to traditional jars. Image credit: Jeb Kegerreis.

The tea brewed in a silicone bag was reported to be just as delicious as tea brewed in a glass jar by the taste testers.

The researchers also noticed that they were getting more gluconic acid with silicone bag brewing compared to glass jars. “We think this acid will become more popular with brewers,” said Jeb Kegerreis, a physical chemist and one of the team’s principal investigators. “Gluconic acid provides acidity without the sour vinegar taste you get from acetic acid, and that may appeal to more tastebuds.”

Because gluconic acid is a product of bacteria fermenting glucose, the researchers investigated how starting with glucose or fructose instead of sucrose changes the kombucha fermentation process and taste. “During the fermentation process, yeast in the SCOBY breaks sucrose into glucose and fructose,” said chemistry undergraduate student Abbi Czarnecki. “By using just glucose or just fructose, we looked at how removing that first step affects the whole brewing process.”

The team found that using glucose as the SCOBY food source created a kombucha with more gluconic acid and minimal ethanol. With fructose, the researchers measured more acetic acid and more ethanol. “If minimising ethanol production is the measure of our success,” said Ian Loscher, a chemistry undergraduate and one of the team’s poster presenters, “fructose failed in that department. Out of all three sugars, it produced the most ethanol.”

Principal investigator John Richardson said the fructose brews tasted sweeter. “I prefer a less sweet kombucha, but it’s not necessarily bad,” he admits. What’s important to the team is sharing what they have discovered about different sugars and fermentation vessels because that information can help brewers create a kombucha that hits all the flavour notes and characteristics they want to aim for.

Visit the ACS Spring 2024 program to learn more about these presentations, ‘Comprehensive comparison of the dynamics of kombucha fermentation in a silicone bag and a glass jar’ and ‘Investigating the impact of sugar source variation on kombucha fermentation’, and other scientific presentations.

Top image credit: iStock.com/LightFieldStudios