Speaking of GOST for Russian okroshka.
In the books of the 1800s "Russian Cooking", "Fasting Table" and even "Domostroy" - they talk only about kvass.
Another thing is that the kvass of today and the kvass of those times are different - back then there was bread kvass, sour kvass, mashed kvass with ginger, berry kvass and malt kvass. Homemade white kvass was used for okroshka - made from raw rye malt and rye flour.
And even before the 14th century in Russia, a mixture of vegetables and herbs was poured with a solution of cabbage or cucumber (especially useful after hawkmoth).
However, the old (pre-revolutionary) okroshka composition was different from the modern version - it included rutabaga, turnips, herbs, and, as usual, potatoes and boiled eggs. In the "rich" version, several types of lean meat were added, and the "poor" okroshka was radish with kvass.
"The Narrative of the Travels of Merchant Men" describes the incident of the merchant Crispan, who tasted "crumbs on a pumpkin" after spending the night with a rich villager near Morum. The merchant decided to try the new product, but in the end he "vomited the offer and shouted, "There is no crumb without kvass! " "He beat the owner. ".
Today they use whey, sour cream, mayonnaise, vinegar, soup, yogurt, mineral water, iron, fruit infusion, sour milk and even beer for dressing - but these are only "parodies of okroshka".
Although, there are parodies in other countries - cold soup in India (with curry, mint and ginger), Uzbek chalop, Bulgarian tartar on yogurt or the Lithuanian version with minced meat and a spoonful of garlic mayonnaise. By the way, because of the Armenian dogramach, there were even stabbings and gunfights on my behalf.
Social surveys conducted in all regions of Russia also confirmed that most of the country's residents (about 70%) prepare okroshka with kvass. Residents of the capital, Moscow, Ryazan, Sverdlovsk and Novosibirsk regions, Primorsky Territory, Kamchatka and half of Crimea residents especially like this version of cold soup in the summer.
Russians from Stavropol, Chechnya, Ingushetia, Kaliningrad, Volgograd, Murmansk regions and again Crimea often prepare okroshka using kefir.