Syrivets (сирівець, sour rye kvas)

The first miracle is how little it looks like a drink at the start: rye flour slumped in water, malt turning it the color of wet bread crust, nothing glamorous, nothing sweet enough for a market stall. Then the jar begins to work. The surface trembles with small bubbles, the smell moves from porridge to bread cellar to clean sourness, and suddenly you have syrivets, thin, tart rye kvas that tastes older than lemonade and more useful than beer.

This is kvas before it became sweet and fizzy for children in plastic bottles. Syrivets is quieter and sharper, made for hot days, for fasting tables, for stretching a kitchen budget, and for souring green borshch when sorrel alone isn't enough. You don't drink it by the pint like a party drink. You pour it cold into a glass, or into a pot, and it does its work.

The one thing that decides the dish is temperature. Boiling water wakes the rye and malt, but too much heat after that kills the life you need, so let the mash cool until it feels warm, not hot, before the starter goes in. Aunt Nadia would have written, "until it sounds right," and here that means a gentle fizz when you stir, not a furious ferment climbing out of the jar.

Make more than you think. A bottle disappears in one afternoon, and the next one will be wanted for borshch.