Sour cream contains 18 to 20 percent fat and is soured by the addition of lactic acid to light cream. In recipes, it can be replaced with whole milk yogurt, which has about 10 percent fat, without a significant difference in texture, but lower fat sour cream or yogurt will yield a less tender cake, and the cake or other baked item will be less delicious. Crème fraîche contains about 39 percent fat, so it is not interchangeable with sour cream except where specified.