Ryazhenka - a fermented milk drink produced from cow's Baked milk (Russian:топлёное молоко, Ukrainian: пряжене молоко, Belarusian: адтопленае малако) is a variety of boiled milk that has been particularly popular in Russia, Ukraine and Belarus.
It is made by simmering milk on low heat for eight hours or longer/, fermented lactic streptococcus cultures. Compared with yogurt it has a delicate flavour fermented drink, especially loved children, its taste is sweet and gentle than the yogurt, and the thick consistency
Besides ryazhenka perfectly quenches thirst, so that is what it along with the water it makes sense to drink in hot weather.