This question comes up often, especially from concerned parents and pregnant women. It's one of the hardest questions to answer due to the complex balance between the bacteria and yeast. Typically there is only a small amount of naturally fermented alcohol in the finished drink. However it can vary and sometimes it does spike under certain circumstances (usually with long term storage or 2nd fermentations). In any case, here are some basic steps to help keep the amount of alcohol low, starting with the most important:
1. Less starting sugar
In simple terms, the glucose in sugar is converted by the yeast to alcohol and CO2. Without sugar, there is no alcohol. Less sugar naturally means less potential alcohol. If you are doing a 2nd ferment, be careful not to put in fresh sugar or juice as they will spike the alcohol significantly.
We recommend about 1 tablespoon of sugar to 1 tablespoon of grains for long term sustainability. 1.5 tablespoons of sugar per 1 tablespoon of grains can make a more active and tastier kefir, but if alcohol is a concern, stick with the 1:1 ratio or even less.
Just keep in mind that the grains need sugar to survive and flourish. However, the grains can do fine for a couple batches with very little sugar. So if you are extra concerned about alcohol or the amount of sugar, you can try the occasional batch with low sugar, but be sure to do a normal batch every couple or so batches to help nourish the grains long term.
Along those lines, try coconut water kefir or coconut ginger beer. It's low sugar and usually low alcohol as well.
2. Drink it fresh
When fermenting, the grains will keep the alcohol in check at all times. As the alcohol is being made it will be used up and converted by the bacteria into acids. Once you take the grains out, (the yeast which is more opportunistic) has a greater potential to thrive and with that, so does the alcohol level. So our recommendation is to drink it as fresh as possible with minimal fridge storage. Long term storage, even really cold storage can slowly increase the alcohol over time.
3. Use an open lid
This is less significant, but it can have a minor impact. When kefir or ginger beer ferment anaerobically with a closed lid or airlock, it tends to make it a little more difficult for some of the bacteria to convert that excess alcohol into acids. It can create a more yeastier type environment which is not usually a concern unless you are looking to keep the alcohol as low as possible.
3. Avoid both hot or cold ferments
When its warm, the yeast respires more which creates more CO2 (bubbles) and less alcohol. On the surface that sounds great. However, with less alcohol available, the bacteria ultimately suffers which then can create an environment that favors the yeast. Excess yeast can lead to excess alcohol as well.
When its cold, the yeast will respire less and create more alcohol. Now this sounds bad, but the balance to this is that it will create an environment that favors the bacteria instead of the yeast.
The bottom line is that the the level of alcohol is unpredictable in both hot and cold environments and has a greater potential to rise with unfavorable conditions. It's best to keep the temperature moderate and the bacteria and yeast in balance, so the alcohol level stays steady.
4. Be wary of excess minerals, supplements and dried fruit
Yeast thrives off minerals and can shift the balance to a more yeastier environment which in turn creates more alcohol. Using 100% dark and mineral rich sugar, excess minerals or dried fruit with too much dark sugar can create a haven for the yeast and subsequent alcohol.
However, keep in mind if there's not enough minerals, then the yeast will respire less and convert more alcohol instead off CO2. Try to strike a good balance between the two. We recommend in our guide to use about 50% cane sugar and 50% of a dark mineral rich sugar to help balance the grains and not let unfavorable yeast conditions occur that will add more alcohol.
Kefir and ginger beer have a complex balance and its really hard to accurately predict the alcohol outcome even though its usually always quite low. And unfortunately there's no easy way to test the alcohol before drinking besides simply trusting your sense of taste. The 2 best ways to lower the amount of alcohol is by starting out with less sugar and drinking it as fresh as possible. Using an open lid, keeping the temperature stable and the mineral load balanced will help keep the alcohol level consistently low. Ultimately, these cultures can easily be enjoyed by all members of the family with just a little care and understanding.