Kvass can make kefir - GOST determined the correct recipe for okroshka.
As known for the shot test, the standard for Russian cuisine determines the specific composition of traditional okroshka. It should include meat, chicken or fish, cucumbers, green onions, herbs and kvass. Therefore, options based on kefir, mineral water or whey are not suitable for this recipe.
At the same time, GOST is voluntary: cafes and restaurants can prepare okroshka according to their recipes, but will not be able to declare that it meets the standard if they deviate from the prescribed composition.