Sterilize a glass jar and any utensils you’ll use by washing them well and rinsing with boiling water; this helps ensure a clean fermentation.
Measure your ingredients: for every 1 cup (240 ml) of Heavy Cream use 1–2 tablespoons of Sour Cream as a starter (adjust proportions up or down depending on how much smetana you want to make).
Bring the Heavy Cream to room temperature (around 20–25°C / 68–77°F) by leaving it out for about 30–60 minutes—this helps the culture develop evenly.
Whisk the room-temperature Heavy Cream together with the Sour Cream starter in the sterilized jar until completely smooth and homogenous.
Cover the jar loosely with a lid or a piece of cheesecloth secured with a rubber band to allow airflow, then leave it at room temperature out of direct sunlight for 12–24 hours. The mixture should thicken and develop a mild tang—warmer rooms will ferment faster.
Once it has thickened and tastes pleasantly tangy, stir gently, close the jar, and refrigerate for at least 6 hours (overnight is best) to chill and firm up further.
Store your homemade smetana in the refrigerator for up to 2 weeks. If you prefer an even thicker texture, strain gently through a fine sieve or cheesecloth for a few hours in the fridge.
