In Russia and some countries of Central and Eastern Europe, the sour cream called smetana is often used for its resistance to curdling in a range of dishes, from savory starters to sweet desserts. Tasting like a thicker and slightly sourer form of sour cream or French creme fraiche, this yogurt-like dairy product is off-white in color and made by leading a precise mixture of dairy liquids through the curdling process. Though adding this cultured milk to a recipe means adding a product with a milk fat percentage of 40 percent or more, it is still considered a low-fat dairy product due to minuscule levels of saturated fats.
Like sour cream and most other cultured milk products, smetana is most often purchased at the grocery store for use in kitchen recipes. It is not readily available in the United States, though it is in Russia and European countries like Finland and Norway. Commercial manufacturers have the benefit of using a pre-mixed assortment of the bacterial enzymes needed to make smetana correctly. To make it at home, cooks will need a small portion of finished smetana to make a larger batch, since it will contain the necessary rennet culture.
One at-home recipe for this type of sour cream uses just a few basic ingredients and a straightforward preparation. For 1 pint (about 600 ml) of product, about 0.5 pint (about 300 ml) each of skim milk and pasteurized cream is heated to a precise 110°F (about 43°C), and then a small amount of smetana is added — as little as 2 tbsp. (about 30 ml). When fully stirred, it is poured into a container and left at room temperature for a half-day or more.
This homemade sour cream can reportedly last in the refrigerator for as long as a week before spoiling. Store-bought versions can last weeks longer, due to added preservatives and airtight conditions. Before it goes bad, it is used in regular or sauce form to complement dishes of every course, from soups and salads to entrees and baked desserts. The cheese is considered particularly useful for withstanding further curdling, a common problem with some other types of sour cream.
The American version of sour cream is regularly substituted for smetana in recipes, with a mixture of cream and buttermilk. Curdling quickly takes place due to the enzymes in the fat of the milk. Another common substitution is called créme fraîche.