Kvas by Best of Low Carb Slavic fermented beverage. Low carb. Kvas: 1 LB dried ray bread, crushed 2 oz fresh yeast 1 tsp. white flour 1 LB sugar (it will go in process of brewing) 1/2 lemon 20 LB boiling water (at least) Pour the dried bread into a big pot of boiling water, cover, let stand for 8 hours. Meanwhile, in a cup of lukewarm water, mix yeast and flour. After 8 hours, drain the bred and add the yeast mixture and sugar. Letstand in a warm place for overnight or for 12 hours. Drain through a cheesecloth, press the remains to squeeze out more liquid, put into bottles with a slice of the lemon in each, close tight and after 3 hours put into a refrigerator. Makes about 2 quart