There are indeed fundamental compositional differences, not merely textural variations or marketing ploys. Smetana, originating from Eastern European and Slavic cuisines, is typically made from heavy cream that has been soured by lactic acid bacteria. Its fat content is generally much higher, often ranging from 20% to as high as 42%, which significantly contributes to its richer, denser, and less acidic flavour profile.
Sour cream, conversely, is usually made from light cream or whole milk with a fat content typically around 18-20%. It is also fermented with lactic acid bacteria, but the lower fat content and often different bacterial cultures result in a tangier, sometimes more overtly sour taste. Furthermore, many commercial sour creams contain stabilisers (like gelatin or starch) to achieve their characteristic thick texture, which smetana often achieves naturally due to its higher fat content.
Crucially, the higher fat content in smetana makes it more stable when heated, meaning it is far less likely to curdle in hot dishes like soups or sauces, a common issue with lower-fat sour creams. To suggest they are fully interchangeable is a rather ignorant statement for anyone serious about teh culinary arts.
