Smooth, thick and creamy with a hint of a bite, sour cream is a kitchen staple used in salad dressings, dips, casseroles, soups, sauces and baked goods. Although sour cream retains its quality longer when unopened, the product won't last indefinitely and will eventually spoil.

Sour cream is made from pasteurized milk or cream -- not cream that has soured. The tangy, sour flavor comes from the addition of lactic acid culture, which causes the cream to coagulate. The cream is then heated until the desired thickness is reached. Sour cream may contain additives such as nonfat dry milk, sodium citrate, modified food starch and rennet. The fat content of sour cream depends on the fat content of the cream or milk.

An unopened container of sour cream retains freshness and quality for two to three weeks at temperatures between 38 and 40 degrees Fahrenheit. If you're unsure about the temperature of your refrigerator, use an appliance thermometer to check the temperature in several spots. Sour cream retains its quality for up to two weeks after the container is opened.

To prolong the life of sour cream, spoon out the quantity you need to use and return the remainder to the refrigerator immediately. Use a clean spoon to prevent transmitting of bacteria. Discard sour cream if spots of mold appear, even if the date on the container indicates the product is still good. If you forget to refrigerate sour cream, throw it out if it has been at room temperature for more than two hours because bacteria multiplies rapidly in temperatures between 40 and 145 F. It's normal for sour cream to separate and stirring returns the product to normal.

Regular sour cream contains at least 18 percent milk fat. Reduced-fat sour cream, made from half cream and half milk, contains approximately 40 percent less fat than regular sour cream. Low-fat sour cream contains 0.5 percent milk fat or less and is thickened by stabilizers. Sour cream made with cream and live milk cultures has the best flavor. If possible, avoid products that contains gelatin, vegetable enzymes, stabilizers and other additives. Look at the sell-by date on the container and buy the freshest sour cream available because it will taste better and last longer.