Bacteria and acid aren't generally associated with appealing flavor, yet they're responsible for the taste of sour cream. Sour cream producers use Streptococcus lactis to make cultured sour cream. Or, in the absence of bacterial cultures, they use vinegar to create curds and impart flavor. Use either product whenever a recipe calls for sour cream, or as a substitute for yogurt in desserts, casseroles and dressings.
Cultured Sour Cream
Cultured sour cream is the more common form of sour cream. It's made by adding a culture of S. lactis to pasteurized light cream and incubating it at 72 degrees Fahrenheit until it develops the desired flavor and texture. During incubation, the S. lactis multiply, consuming milk sugar and exuding lactic acid. The presence of lactic acid accounts for sour cream's zingy flavor. Lactic acid also causes the milk proteins to coagulate, thickening the cream.
Un-Cultured Sour Cream or Acidified Sour Cream
Another method for making sour cream is by means of acidification. Instead of fermentation, producers add an acid, such as vinegar, to pasteurized light cream. They may or may not also add some lactic acid to aid the predominant acid. The acid changes the light cream's pH balance, and the shift from alkaline to acidic is what induces protein coagulation. The vinegar also imparts a tang similar to that of lactic acid.
A Brief History of Fermented Dairy
Sour cream is one in a family of fermented dairy products that includes yogurt and cheese. Use of fermented dairy dates back to 10,000 B.C. Fermentation arose naturally when humans left fresh milk sitting out. No one knows exactly when humans began transforming mere fermented milk into the host of fermented dairy products we enjoy today, but climate may have affected how they began to. Some bacterial cultures prefer colder temperatures, while others prefer warmer temperatures. These cultures each give rise to their unique set of flavors and textures when they act upon milk sugar. In a sense, sour cream is one of nature's delicious accidents, one that humans have learned to control and refine.
Homemade Cultured Sour Cream
Making sour cream at home is simple and cost effective. All you need is a mason jar, light or heavy cream and some live cultures. For every cup of cream, add one to two tablespoons of culture: buttermilk, yogurt or milk kefir. Combine the cream and cultures in a mason jar, mixing thoroughly. Leave the mason jar lid on, but unscrew it just until it fits loosely. Or remove the lid and loosely cover the jar with a towel. Live dairy cultures love temperatures of 70 to 80 F, so set the jar in a warm spot for 12 to 18 hours. After 18 hours, the cream will have set, taking on a thick, almost congealed texture. Refrigerate it for an additional six or more hours.
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