Butter is made from the cream portion of cow's milk. The cream is churned until fat globules come together to form a semisolid mass. It is used as a spread, a medium for browning and sautéing, and as an integral ingredient in pastries, cakes, confections and frostings.

By law, butter must be at least 80 percent butterfat and have less than 16 percent water. The rest is milk solids. It is the milk solids that will burn if subjected to high heat. It can be dyed with annatto, a natural coloring agent. Butter is scored by the United States Department of Agriculture (USDA) and assigned quality grades based on flavor, body, texture, color and salt. Grade AA (93 score) is the highest grade and the most common grade available in the retail market. Grade A (92 score) is also sold. Lower grades are rarely seen in supermarkets.

Butter is usually sold in one-pound packages that contain four (4-ounce) sticks. Each stick equals 8 tablespoons or 1/2 cup. Packages should be stamped with a freshness date. At home, butter should be stored in the coldest part of the refrigerator or frozen. Either way, wrap it tightly since it picks up other flavors.

Unsalted and salted butter are available. Unsalted butter has a more delicate flavor and is preferred by many cooks, especially for sauces and baking. Although it varies by manufacturer, salted butter has about 1-1/2 teaspoons added salt per pound. Whipped butter, sold in tubs, has air beaten into it so it is spreadable at refrigerator temperature. Do not substitute whipped butter for regular butter in baked goods. Butter-margarine blends combine the two in varying proportions to produce a product with fewer grams of cholesterol while retaining the flavor of butter. As long as the blend has the same percentage of fat as butter (80), it can be used interchangeably with butter.