Kvass is very similar to cask. Simple to prepare. A delicious fizzy drink.
The basic ingredients.
4 tbsp. sugar melt to a brown colour.
To warm water add sugar, melted sugar, yeast and citric acid. Mix well until dissolved.
Pour kvass in plastic bottles, tightly close lids and leave for a day in a warm place in a horizontal position. If the place is warm enough, you can leave for another 2 days.