Source: message header lost, posted to r.c.b., 2/11/92
Kvass is very refreshing on a hot summer's day and is quickly made from black bread and yeast. It is quite like weak beer and is fermented and slightly alcoholic, but must be stored in the refrigerator using corks, not screw-in stoppers or else it will go on fermenting and blow.
This, to me, looks very similar to the Sumerian recipe which Anchor Brewery of San Francisco recreated a couple of years ago.
Add the sugar and yeast, mix, cover and leave for ten hours. Pour the drink into clean bottles, and three sultanas to each, put the corks and tie them down---then refrigerate immediately.