Milk kefir is a pretty common sight in the dairy aisle these days—or at least it is in California. Much more mysterious is its lactose-free cousin, water kefir. Both drinks are fermented with similar SCOBYs (symbiotic colonies of bacteria and yeast), but milk kefir grains feed on the natural sugars in the milk while water kefir needs additional sugar or fruit juice to get going. Mary Karlin provides recipes for both in her new cookbook, Mastering Fermentatio. Today, we're trying our hand at the water-based version.