Butter Basics

• Butter's distinctively rich flavor -- as well as many of its quirks in cooking and baking -- derives from its makeup. Ordinary table butter isn't a pure fat, but a mixture of butterfat, water and milk solids. The fat gives it richness, the milk solids contribute flavor, and the water helps make it spreadable at room temperature. Ordinarily fat and water don't mix, but in butter they form a stable emulsion until the butter is heated. Then, the water separates out and leaves the fat behind. That's what's happening when butter fizzes in your skillet. When the bubbling stops, the water has all boiled away.

Whipping Butter

• The fats in butter crystallize at slightly different temperatures, but when the butter is fresh from your refrigerator they're all quite rigid. As the butter warms, some of the fats soften, making it spreadable, while others remain firm enough to hold the butter's shape. If you whip the cold butter in a food processor or stand mixer, as you would when creaming it for a cake or cookies, the processor's blade or mixer's whisk will carve out trails of air though the fat molecules. The firm butter traps the air, and as you whip the butter it gradually becomes light and fluffy. It's spreadable even at low temperatures, and you'll use less on your toast.

Adding Water

• If you want to further reduce butter's fat content, or make it lighter and more spreadable, adding cold water is one way to do that. All you're really doing is increasing the butter's water content from its natural 15 to 18 percent, without changing the butter in any meaningful way. You can use 1 to 2 fluid ounces of water per pound of butter, or up to 1/4 cup. Whip the butter until it's light and fluffy, then add the water in a slow, steady stream. Scrape down the sides regularly and keep whipping until the water is fully incorporated. You won't notice any difference when using the butter on bread or cooked vegetables, but it can soften your toast as it melts.

Alternatives

• Aside from water, you can use a variety of other ingredients to soften and extend your whipped butter, depending on your intended usage. For example, you can whip the same amount of whole, skimmed or partially skimmed milk into your butter, which retains its full flavor. To simulate the tang of European-style cultured butter, whip in buttermilk instead. If you want a whipped butter that works well on toast but contains less saturated fat, whip in a neutral-flavored oil such as sunflower, canola or grapeseed oil. It softens the butter admirably, but won't make your toast soften the way water or milk might.