Curdling can occur in any dairy product, as milk proteins coagulate and lump together. This causes separation of the curds (the protein lumps) from the remaining liquid. Several factors can cause curdling, including the addition of acid, tannin or bacteria, and a high cooking temperature. Sour cream is already slightly acidic. Commercial products contain lactic-acid-forming bacteria, and homemade sour cream often has acid added directly, in the form of lemon juice or vinegar. Sour cream can to curdle when made into a warm sauce, but you can take steps to prevent this.
Check for curdling agents in your recipe. If you are adding acid, in the form of lemon or lime juice, or tannin, in the form of coffee, tea or potatoes, try not to heat the sauce. It will be warmed through if used cold as a garnish on hot food.
Heat sour cream sauces gently and do not allow them to boil. Stir constantly with a wooden spoon to prevent the sauce on the base of your pan from getting hotter than the rest.
Add a small amount of flour to your sour cream sauce. This will help to prevent curdling. Flour coats the proteins and stops them from collecting together.
If your sauce does curdle, remove it completely from the heat and whisk vigorously to reincorporate the proteins.
Substitute thickened Greek yoghurt for sour cream; it is less likely to curdle. Stir sour cream sauces into your dish at the end of their cooking time instead of heating them separately.
Sour cream sauces will separate when frozen. If possible, freeze a dish before you add the sauce. You can complete it once thawed for use.