Milk that is not homogenized (a process whereby all the
particles are broken down to the same size so that they mix
together) will naturally separate into a top layer, which we call
cream, and a low-fat liquid below. Butter is the result of
churning the top layer of cream until it reaches a semi-solid
state. The liquid left over from this process is buttermilk,
though most commercial buttermilk today is made by adding certain
bacteria to nonfat or low-fat milk.
The USDA grades butter on flavor, body, texture, color, and
salt content. AA is the best, with A, B, and C following in
decreasing desirability. Butter that is marked "light" or "reduced
fat" has had water, gelatin, and skim milk added. Butter is
available salted and unsalted; unsalted butter is usually a better
option for both cooking and baking, as it gives you
greater control over a dish's seasoning.
An increasing number of artisanal butters are on the market,
and they are worth seeking out for their unique flavors and
textures. Some, like Vermont Butter and Cheese's cultured butter, are made
in the European style that churns crème fraîche rather than regular cream. Check out our other picks for
artisanal butters.
An unopened package of unsalted butter will keep for 1 to 2
months in the refrigerator. Because salt acts as a preservative,
salted butter will keep longer (2 to 3 months for an unopened
package). The "use by" date printed on the package can provide a
helpful guideline. Older butter won't be dangerous but the flavor
can start to deteriorate. Once the butter is opened, it should be
used within 3 weeks or frozen. Both salted and unsalted butter
stores well in the freezer for up to 6 months. Wrap butter tightly
because it can absorb other flavors easily.