As kefir was normally the drink for adults (at least for the diet conscious Soviet women) – Ryazhenka, popular also as the baked milk was exclusively for the children. Ryazhenka is the other and the traditional Russian (some say Ukrainian) fermented dairy product. Ryazhenka when mixed with one spoon of sugar, used to be the treat for a Soviet child. Sometimes Ryazhenka is translated to be baked milk because for preparing it you need to bake the milk in the low heat oven.
Dairy products have always been one of the major highlights of the Russian cuisine, and there is quite a good list of products which are not easily found in U.S. but are pretty common here. Two of them are the kefir and the Ryazhenka.
Kefir resembles a cross between the milk and the yogurt, with a slightly chunky texture, and bears a sharp bite on it. It is prepared by using a bacteria culture for fermenting milk, and historically, people made this at home only. However, now a day most of the Russians buy packaged kefir from the grocery store. Ryazhenka is similar to taste like the kefir but is milder. It is not as sharp, but a bit sharper than the plain yogurt, and it possesses an impressive smooth texture. Kefir is thus pure white in colour, while the Ryazhenka bears a brown tint. The reason behind it is because Ryazhenka is normally baked fermented milk. It was made historically by baking fermented milk in any oven or with low heat on a stove for long hours, but then again, the Russians today just purchase it from a grocery store.
Ryazhenka is made by pasteurising the milk and later simmering it on the low heat for as long as eight hours or even longer. Historically, it was prepared by placing one clay pot (or the glechik) with the milk in a traditional Russian oven for one whole day till it has been coated with the brown crust. Prolonged exposure to the heat causes a Maillard reaction between milk's amino acids and glucose or sugars. This results in the evolution of melanoidin compound that offers a creamy color with a caramel flavor. As a result a good amount of moisture evaporates, this results in a change in the consistency. In the household method of production, the sour cream (smetana) is added subsequently to trigger the fermentation. In the modern industrial production, the pure thermophile bacterial culture has been added instead. The mixture is then placed in a warm place. The fermentation takes place at temperatures above 40°C / 100°F and takes about three to six hours.
The fat content of the industrially made Ryazhenka is typically 3.5−4%, however, in general, it's permitted to vary from <0.5% (if prepared from what we know as the skimmed milk) up to say 8.9%. The protein content is a minimum 3%. The carbohydrate content, generally about 4−5%. Like the scalded milk, Ryazhenka is also free of the harmful bacteria and the enzymes and may be safely stored at room temperature for at the most- forty hours.