Whey, the nutritious by-product of the cheesemaking and yogurtmaking process, is full of Lactobacilli, so it serves as a fantastic fermentation starter. This recipe is inspired by rosl, a Jewish specialty from the Ukraine that calls for pickling beets in brine. The sweet, spiced beets are seasoned with orange zest and mustard seeds, and make for a delicious accompaniment to roast meats or fish. You can purchase whey online or make your own by draining store-bought live-culture yogurt in a cheesecloth-lined mesh sieve over a bowl: The drained liquid is whey. This recipe first appeared in our October 2011 issue along with Sara Dickerman's article Preserving Plenty.