★★★★★
A simple way to make this is just to place in a jar some dried out rye sourdough bread slices, (slices can be dried in the oven or even just on the counter). Add boiling water to fill the jar. One slice of the bread can be added later when the water not that hot. A teaspoon of salt can also be added to the mixture. Put a lid on the jar. (Maybe mix it every day.) After 3-5 days the water will have a pleasant tangy taste. (The bread can be removed after a day or two or earlier.)
This is not a professional kvass, which also has sugar or honey and some yeast added to it.
There is also beet kvass that is also helpful for many.
