Butter Facts

Butter is made from heavy cream by churning it into a solid and then removing the leftover buttermilk. Butter is an emulsion, a combination of two liquids that would not ordinarily mix, like oil and water. Cream is an oil-in-water emulsion, meaning tiny droplets of fat are ensconced in water, which is why it is a liquid rather than a solid. Butter, however, is the other way around. When cream is churned, the emulsion flips to become a water-in-oil emulsion, concentrating the fat and separating out the excess water. This—along with the fact that butterfat is largely saturated fat, which is more stable and given to solidify than unsaturated fat—is why butter is a solid.

There are a number of options when it comes to buying butter: regular or premium, cultured or uncultured, salted or unsalted. By law, butter manufactured in the United States contains at least 80 percent fat. The remainder is made up of water (13 to 19 percent), milk solids (namely, protein and lactose), and salt, which may be added as a preservative and flavoring. Chemically, butterfat is made of molecules called triglycerides that are composed of one molecule of glycerol attached to three molecules of fatty acids. Many of the fatty acids in butterfat are saturated, which provides the fat with a crystalline structure that melts slightly above room temperature. Butterfat also contains up to 3 percent natural emulsifiers such as lecithin, and fat-soluble vitamin A. Premium, European-style butter has a higher fat content—at least 82 percent, and up to 86 percent. Higher-fat butter has a firmer consistency and is slower to melt.

Butter may be manufactured with or without salt. The salt acts as a preservative and adds flavor. Salted butter contains anywhere from 1.6 to 2.5 percent added salt. The level of salt is determined by the manufacturer and can vary among brands. In addition, salted butter almost always contains more water. For these reasons, when cooking—and especially when baking—we prefer to use unsalted butter.

Butter can be difficult to work with in the kitchen because it changes so rapidly with temperature, beginning to soften between 60 and 68 degrees, beginning to melt around 84 degrees, and becoming completely melted at about 94 degrees. It grows quite firm—too firm for many applications—when refrigerated (at around 35 degrees). Getting butter's texture right can be a delicate balance. It must be chilled, but not too firm or soft, to achieve the best flakiness and volume for laminated pastries like the croissants in this class. The best temperature for creaming butter, which adds air pockets for optimal lift, is between 65 and 68 degrees. Melting butter, which allows the water in the butter to interact with flour to form gluten, is key in certain bread recipes. Butter that is browned develops an appealing nutty flavor and deep golden color because the protein and lactose undergo the Maillard reaction producing both color and flavor.