The story of Jews in the Diaspora was one of making things stretch. Clothes, food, wood, coal. All of these things were to have every last drop of use squeezed out of them, in the case of Kvass, quite literally. Kvass was a rough homemade liquor made out of the stale ends of Russian black bread.
Where some housewives might have thrown those bits of stale bread to the birds, Jewish housewives soaked them in water, squeezed them out, then added yeast, sugar, mint, and raisins to the resulting murky brown water. This was a “spirited” way to use up old bread and an interesting Jewish economy.