Before we get into what one can do to reduce the alcohol levels in your kombucha, we must take a look at how the whole process of alcohol production works.
When the SCOBY is placed into a new batch of sweet tea, the yeasts immediately begin to work on any sugar which is present. As they gobble it up, they in turn produce alcohol. This is a good thing, because the bacterial component of the SCOBY needs this alcohol as its food source.
Kombucha usually has trace amounts of alcohol present. However if the yeasts get out of hand, or the bacteria are sluggish, then these residual levels of alcohol can rise.
If you are looking to lower the residual alcohol levels in your kombucha then it is possible to influence the yeasts and bacteria to achieve this. The basic strategy is to inhibit the yeasts a bit, while encouraging the bacteria.
Yeasts like warm temps and sugar to eat. By manipulating these conditions it is possible to slow their alcohol production somewhat. In addition, while the yeasts and bacteria do have a symbiotic relationship, they are also in competition. Therefore if the yeasts are subdued slightly (they usually have the upperhand somewhat) , then the bacteria will be able to flourish. The more of them there are, the more alcohol will be eaten up.
However do be aware that if one subdues the yeasts to the point where there is no alcohol produced, then the bacteria will not have anything to eat and will not do well either. In that situation the whole culture will lose vigor. So whatever you do, do in moderation.
The simplest step to discouraging the yeasts a little bit is to lower the temp at which you are brewing. Kombucha does best at 69o Fahrenheit (22o Celsius) and 84o Fahrenheit (29o Celsius). The bacteria prefer the lower end of this range and the yeasts prefer the upper end.
If the temperature is already fairly moderate in your house, then this might just be a matter of moving your kombucha brewing setup to a colder part of the house, such as a backroom which gets less direct sunlight. If it is severely hot where you and your kombucha are, then you might want to look at Warm Weather SCOBY Care: Brewing Kombucha in Hot Weather.
The perfect temperature which you can aim for is 73 degrees Fahrenheit (23 degrees Celsius). But if you are under this a little it’s ok.
Starter liquid from the top? By this I mean, when you are setting up new ferments, take your starter liquid from the top of the container in which it is in. If you are using some of your newly made kombucha as starter liquid, then scoop off the top however much you will need, before doing decanting and bottling.
The reason for doing this is due to the fact that the free floating yeasts which hang around in kombucha tend to settle and accumulate on the bottom of whichever container they are in. So, by taking starter liquid from the top and not from the bottom, you will incorporate less into your new batch. Which means that there will be slightly less yeasts to produce alcohol.
Strong tea provides lots of things called sterols which the yeasts need to reproduce. If there is not enough of them in the tea, then they will be forced to make their own. This will cause the yeasts to have less energy to convert sugar into alcohol, as they are busy with sterol production as well.
If you are wondering exactly what is weak, then no more than three bags of tea to a quart of water with a 10 minute steep is a good example.
In beer brewing – where alcohol production is desired – there is a phenomenon called the Crab Tree effect. This occurs when there is too much sugar present for the yeasts and they go into a sluggish state from overeating. This is why – when trying to create more alcohol in kombucha, one is advised to stagger the sugar feeding. This can result in more sugar added overall, but at intervals to keep the yeasts on overdrive. If you want to yeasts to underperform, then you can try the opposite technique.
What to do: Use a bit more sugar than usual for your batch. Add it all at once in the beginning.
To compound this strategy, if you are doing second ferments, then do not add any additional sugar to these. This is particularly important because of the absence of the SCOBY.
The SCOBY acts as the housing for the bacteria within kombucha, while a lot of the yeasts are instead free floating. This means that when a second ferment takes place, there are a larger portion of yeasts to bacteria than in the primary ferment. If there is a lot of sugar present, then the yeasts will have a feast, and produce lots of alcohol. However there will not be the usual amount of bacteria to consume the alcohol and turn it into organic acids.
If you see long strings of brown yeast colonies attached to your SCOBY, pull them off.
Note on decreasing yeasts: For the purpose of lowering potentially alcohol levels within your kombucha it is desirable to calm down the yeasts and have a bacteria heavy ferment. However as mentioned above, the very bacteria you wish to promote do need some yeasts in order to survive and brew the kombucha. So be careful of going overboard with this line of brewing.
If there are very few free floating yeasts in your kombucha, and they are taking a while to develop, then it might be a good idea to stop these techniques until such a time as the yeasts are more active.
A lot of the things which you can do to encourage the bacteria have been covered above under discouraging the yeasts. Drop the temperature if needs be, use weak tea, and use sugar as a tool with which to manipulate the yeasts. However there a couple more tips which you can use to encourage the bacteria.
If you increase the surface area of your brewing vessel, the SCOBY will grow to cover this expanded surface area. Because the bacteria live within the SCOBY, and a lot of the yeasts float free, this means that the bacteria to yeasts ratio will rise. This, however, will only stand true if the volume of kombucha being brewed does not increase in conjunction.
Once again, by increasing the bacteria to yeasts ration, you will end up with more bacteria to eat up the alcohol, and less yeasts to produce it.
Because the bacteria live in the SCOBY, you can take any old cultures you want to chuck out, and squeeze any liquid that is in them straight into your brewing kombucha. This is another trick which will boost the bacterial component of your kombucha. And hopefully with that drop alcohol levels.
If for certain reasons you need to make completely alcohol free kombucha, then this too is possible. However, doing so will kill all probiotic organisms in the kombucha, and render it useless for probiotic purposes. If this is not a consideration, then making 100% alcohol free kombucha is fairly simple. However if you wish to retain the beneficial probiotic microbial elements, then you can only lower alcohol levels to trace amounts, not completely eradicate them.
The easiest way to render homemade kombucha alcohol free is to pasteurize it. There are two methods which you can try.
Before bottling your kombucha, heat it in a large pot. The kombucha must reach at least 140 degrees Fahrenheit (60 degrees Celsius) and should not exceed 160 degrees Fahrenheit (71 degrees Celsius). Use a cooking thermometer to monitor the temperature.
Bottle the kombucha as usual, and then submerge the bottles in hot water. Once again the kombucha within the bottles must reach reach at least 140 degrees Fahrenheit (60 degrees Celsius) and should not exceed 160 degrees Fahrenheit (71 degrees Celsius). To monitor this, unscrew the cap of one bottle and insert a cooking thermometer to test the temperature.
While pasteurization does render the kombucha devoid of probiotics, the kombucha will still retain its other healthful elements. If the probiotic benefits are very important to you, then you can also consider consuming kefir, yoghurt, kvass or rejuvelac as alcohol-free options.
Kombucha which is unpasteurized will always contain trace amounts of alcohol. Certain conditions can cause these to rise, to the point where they are above the 0,05% threshold. However with a little bit of knowledge and some experimentation, you can also manipulate your kombucha into producing less alcohol. This is important is you are making kombucha to sell, and do not want to register it as an alcoholic beverage. Or perhaps you wish to reduce the alcohol content for your own consumption.
If you need to make kombucha which is 100% alcohol-free, then this too is possible with pasteurization. Unfortunately, pasteurization will result in a loss of probiotic qualities. However the kombucha will still retain its other healthful components such as vitamins and natural acids.