How to Reduce Alcohol In Kombucha

Consistently brewing good kombucha is just plain hard. Once you start serving to others, you start to worry if the beverage you're making is really low alcohol like you keep touting. Whether it's for religious or health reasons, many people are drawn to kombucha specifically because it is marketed as alcohol-free. From simple biology and chemistry, kombucha will have some amount of alcohol. It is on us to control the alcohol to the best of our ability. That is what I will help you with in this article.

My name is Nick. I have worked with dozens of kombucha brewers over the last eight years to control alcohol levels. For my PhD, I studied genetics in non-conventional yeast. Controlling alcohol is really an easy practice once you understand the fundamentals of the biology and the physics at play. Let's start there.

Yeast make alcohol from sugar. Bacteria make acids from sugar and/or alcohol. This is the fundamental metabolism that occurs in a SCOBY. To deduce alcohol reduction methods, we need to know a little more about how these little bugs live. Yeast cells are roughly 5 μm, 200X smaller than a poppy seed. Typically, yeast cells are pretty resilient because, unlike bacteria, they have a cell wall made of a strong polymer called chitin. If you've seen those brown strings hanging down in kombucha, that is yeast accumulation. Sometimes the yeast flocculate, or settle, at the bottom of the vessel. Strong growth between 16℃ and 40℃ is common, but temperatures closer to 28℃ typically produce the fastest growth for most strains. That being said, there is a large amount of diversity within yeast and faster growth does not necessarily produce the best flavor.

Bacteria are much smaller, approximately 1 μm on average. When I worked with bacteria in my academic lab, I often joked that just looking at bacteria the wrong way will cause them to lyse, or burst open. Bacteria do not have strong cell walls like yeast. The gelatinous pellicle on top of kombucha is made of a type of cellulose produced by certain bacteria. It may be safe to assume there are higher concentrations of bacteria than yeast in the pellicle. Some species of bacteria can grow happily at temperatures around 50℃, but most prefer closer to 30℃. The specific bacteria in kombucha typically prefer lower pH ranges than the yeast can handle.

The simple strategy to reduce alcohol in kombucha is to limit yeast growth and encourage bacterial growth. How do we do that?

Let's just start with the most powerful change you can make: Use an old, sour starter. Let that kombucha brew for at least one month, maybe a few months. You'll get an incredibly sour solution that should be very low in yeast and very high in bacteria. There is no more sugar left for the yeast to consume and the pH is so low only the bacteria can survive. If you use this vinegar as your starter, your alcohol content should stay low and your product will be much more consistent batch to batch. Starting with more bacteria and less yeast gives the bacteria a huge headstart to consume any alcohol that the yeast produce as fast as possible.

The next strategy is to just get rid of the yeast! This is more helpful if you tend to get higher levels of alcohol in your secondary fermentation or while your product is sitting on shelves. Try different size filters to remove the majority of the yeast, but still keep most of the bacteria. Remember, yeast are much larger than bacteria! If there are solid particles in your cans or bottles, you almost certainly are higher than 0.5% ABV. Even getting rid of the visible particles can drastically increase the shelf life of your product.

Think hard about your vessel aspect ratio, that's the ratio of the height to the width. High aspect ratio vessels are tall and skinny and low aspect ratio vessels are flat and wide. Increasing a vessel's aspect ratio almost always results in higher alcohol. Wide, shallow vessels allow much more surface area relative to the total volume, so oxygen can dissolve into the liquid. Yeast produce less ethanol in aerobic, or oxygen rich, conditions and the bacteria in kombucha need oxygen to survive. I haven't met a brewer who explicitly told me they sparge air into their vessels, but I think it would be very worth it to try. To be clear, you would need on the order of 10 L/hour/L of volume to have noticeable effects.

Keep in mind, any changes made to the brewing process could drastically change the flavor of your product. Everyone's SCOBY is different. If I were to start a brewery again, I would start there. Find a SCOBY that produces low levels of alcohol! But what this also means is that YOU have to do these experiments to optimize for flavor and lower alcohol. There is no one easy solution.

At the root of it all, you need to test your kombucha for alcohol. The best way to do this will always be to find a lab that knows about kombucha (Cultured Analysis if you're in the US) that does GC-FID testing for ethanol. However, the turnaround time for lab testing will never be instant. Of course I am an advocate of my own alcohol detector that I invented when I needed to know the alcohol of my own kombucha. The more you test for alcohol, the more you will understand the process. The Rare Combinations Alcohol Detector is by far the easiest and most affordable in-house testing option. OK, that's all the self-promotion I'll do.