1 l milk
2-3 tbsp sour cream
Bring milk to boil, and pour the boiling milk in a thermos.
Let sit overnight.
Then, pour the milk from the thermos into a glass jar, and let cool to 40 C (104 F).
Pour half of the glass in a separate dish, stir thoroughly with sour cream, and then pour back into the glass jar.
Let sit at room temperature for 2 – 3 hours.
Ryazhenka is ready.
Then, keep in a refrigerator.