Why Did My Kefir Soda Explode?
There are many different kinds of fermented beverages (beer, wine, kombucha, water kefir, lacto-fermented beverages, etc.), but they all have one thing in common. They all require the addition of a fermentable sugar to produce the desired result: lactic acid and carbonation. The bacteria and/or yeast involved in the fermentation process convert the sugar molecules (carbohydrates) into lactic acid, carbon dioxide, and sometimes alcohol. (In the case of beer and wine, yeast organisms produce considerable alcohol, but the bacteria in kefir grains, kombucha scobys, and lacto-fermentation convert the sugar primarily into lactic acid instead of alcohol. Kombucha and water kefir do contain very small amounts of alcohol because they are cultures of yeast and bacteria combined, and even lactic fermentation without yeast can produce trace amounts of ethanol.)
Fermentable sugars are the sugars most of us are familiar with: sucrose in table sugar, glucose (also called dextrose) in honey or corn syrup, fructose in fruit and fruit juices, lactose in milk, and maltose in malted grains. Fruit and fruit juices are commonly used for making kefir sodas since they add flavor as well as a fermentable sugar. Therein lies a potential problem.
Fructose is highly fermentable. In the process of converting fructose to lactic acid, the bacteria and yeast produce a large amount of carbon dioxide. That’s great for producing a fun and bubbly beverage, but it can easily become so effervescent that caution must be used when storing the beverage in a tightly capped bottle.
Under proper refrigeration the bacterial action is inhibited, but at room temperature (even cool room temperature), there is enough carbon dioxide produced to cause a capped bottle to explode under the pressure. Even refrigerated bottles may spray out uncontrollably when opened, so it is wise to use caution when opening a bottle of kefir soda made with fruit or fruit juice.
As some people have learned from experience, a bottle of kefir soda that has been stored for several weeks in the refrigerator is best opened outside. Pineapple juice and dehydrated fruit seem to be quite lively ingredients when it comes to producing over-exuberant effervescence.
Here are a few tips for fermenting water kefir with dehydrated fruit or fruit juices:
Use airlocks for the initial fermentation. When your brew has reached the desired level of fermentation, bottle it in flip-top bottles to preserve the bubbles. Leave the bottles at room temperature no more than four hours before moving to the refrigerator.
If you will not be consuming all of the beverage within a week, loosen the lid periodically to allow some of the gas to escape. Products fermented with fructose continue to ferment for quite some time, although at a much slower rate in the refrigerator.
Check the temperature of your refrigerator. If you are storing your beverage in an extra refrigerator this is especially important, since you might not notice right away if the refrigerator has quit working properly. It is possible for a bottle to explode in an unattended refrigerator that is not staying under 40°F. This can make for quite a messy clean-up!
Kefir sodas are delicious, nutritious and a great alternative to commercial sodas. Just be sure to exercise a little caution when storing them so you can enjoy the bubbles in your glass instead of on the ceiling.