Sour cream is made by adding lactic acid bacteria to light cream that has been brought to room temperature. The mixture is covered and allowed to sit in a warm place – ideally at 72 degrees Fahrenheit -- for 24 hours as it thickens and develops its slightly sour taste. Make your own cultured sour cream by adding either buttermilk or kefir grains to light cream that is at least 18 percent milk fat. Refrigerate cultured cream in a covered container and gently stir any liquid separation back into the cream.

Crème fraiche is made with heavy cream that has been cultured and is similar to sour cream, but with a higher butterfat content. To make crème fraiche at home, start by sanitizing a jar or container, and warm your heavy cream to 86 degrees F. Pour the warmed cream along with your culture into the clean jar and mix well. Allow this mixture to incubate in a warm place for 12 hours. When making cream fraiche, you can use buttermilk or yogurt with active, live cultures as a culture. Or purchase culture starters from cheese-making supply companies.

Use sour cream and crème fraiche to thicken and enrich sauces, soups and stews.
Because its low milk-fat content allows it to break down after prolonged exposure to heat, sour cream is best when added to a sauce or dish at the end of cooking. Crème fraiche, with its higher milk-fat content, is much sturdier and won’t curdle, making it the ideal choice for cream sauces and soups.

Sour cream forms the base for dips and salad dressings, and serves as a topping for baked potatoes. It adds moistness and flavor to baked goods, such as muffins and quick breads. Crème fraiche can be whipped and sweetened for use as a tangy dessert topping. It is also rich enough to be used as a spread in place of butter.