Fruit juice kefir can be made with either water kefir grains, milk kefir grains or a powdered kefir starter culture. We recommend using water kefir grains for two reasons. Water kefir grains are accustomed to being used with sugar water which is more similar to juice than is milk. Milk kefir grains can be converted to be used with fruit juice but be aware that once they are converted, you will not be able to return them to a milk-based medium. Water kefir grains however can go back and forth between sugar water and juice given some time and adjustment (see below). Kefir grains are also reusable to make batch after batch where as the powdered kefir starter culture has a more limited lifespan.
To make fruit juice kefir, add water kefir grains to the fruit juice (either 100% juice or a diluted juice). We do recommend using organic juice whenever possible to avoid the chemicals present in commercial juice which could damage the kefir grains. Allow the fruit juice kefir to ferment for 24-72 hours. Keep in mind that the longer the juice ferments, the higher the alcohol content. We do recommend that if you are making fruit juice kefir for children, fermentation should be limited to a 24-48 hour period. If you are looking for a more “adult” beverage, a longer fermentation period may be desirable. Once the fermentation period is complete, remove the kefir grains and place them in fresh juice or sugar water.
A couple of caveats: First, juice tends to be very hard on water kefir grains. Although they can be used repeatedly in a juice medium, they should be returned to plain sugar water occasionally to revitalize them. Keep in mind that kefir grains that have cultured in fruit juice and are then returned to sugar water make a very unpleasant tasting sugar water kefir for a period of time, so don’t plan on alternating batches of fruit juice and sugar water while still having delicious sugar water kefir to drink. Also, it is highly unlikely that water kefir grains used with fruit juice will multiply and the fruit juice kefir grains will likely have a significant shorter lifespan than kefir grains cultured in sugar water.
We recommend whenever possible to keep two separate sets of water kefir grains: one for sugar water and one for juice (each set can be stored in sugar water in the fridge when not in use). You can accomplish this by purchasing two sets of kefir grains or by waiting until your set of kefir grains multiplies to the point you can use 3 T. of kefir grains for sugar water and 3 T. of kefir grains for fruit juice. This allows you to make both fruit juice kefir and sugar water kefir without interruption.