Peanut butter's palate-pleasing flavor and rich, smooth texture make it a perennial favorite, especially in households with children. It's also a frugal source of durable protein, which -- unlike meats or dairy products -- is shelf-stable at room temperatures. Mainstream commercial peanut butters don't require refrigeration to retain their fresh flavor, though in some cases you might make a deliberate choice to keep them cold.
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Peanut butter typically enjoys a room-temperature shelf life of three to four months, after which it will gradually begin to lose its fresh flavor and can eventually become rancid. Refrigerating the spread roughly doubles its shelf life, a significant benefit if you enjoy its gooey richness only occasionally. Unfortunately, refrigerated peanut butter is stiff and hard to spread, especially on soft bread. One option is to buy peanut butter only in the smallest containers, so you'll use it up quickly. Alternatively, refrigerate the large -- and more economical -- size, then keep a portion at room temperature in your pantry in a smaller container.
All-natural peanut butters, containing nothing but peanuts and -- sometimes -- a modest quantity of salt, are a special case. They tend to separate between uses, creating a layer of dense peanut butter with oil floating on top. Refrigerating the butter, once stirred, slows that process. Natural peanut butters may also develop musty or stale flavors more quickly than their preservative-laden mainstream counterparts, a second argument for refrigeration. If you grind your own peanut butter in-store, keep it refrigerated. While commercial peanut butters are rigidly tested, peanuts in your bulk-food store might contain the mold that produces carcinogenic aflatoxins.