For many cooks and bakers, time constraints and other challenges can make it difficult to keep the refrigerator and pantry fully stocked. If you only have time to cook or bake occasionally, even relatively long-storing ingredients such as flour might reach the end of their usable life before you use them up. Over time, flour can become musty or rancid, and shouldn't be used in your baking.
Storage Life and Label Dating
If you buy your flour packaged rather than in bulk, its bag will usually be imprinted with a freshness date. It has nothing to do with food safety -- it's simply the miller's estimate of how long your flour will retain its best flavor. It's a rather conservative measure and, in practice, your flour's storage life depends on conditions in your pantry. White flour can still be usable up to a year after it's purchased, though six to eight months is a safer estimate. Whole-wheat flour has roughly half the lifespan of white flour, because of its higher oil content.
Your Nose Knows
If you're uncertain how old your flour is or whether it's still usable, just use your common sense. Old flour is sometimes infested with insect life -- primarily the flour beetle -- and that's reason enough to discard it immediately. Your flour might also have a sharply rancid smell, especially if it's stone-ground or whole wheat. Those flours contain more of the grain's oily germ and bran, which oxidize and produce off-flavors and odors. White flour develops milder but still unpleasant musty odors, and can also absorb moldy and musty flavors from its surroundings. When in doubt, mix some of the flour with hot water and sniff it again. Any "off" odors will be more obvious in the heated paste.
Attempting to use dubious flour is usually a bad idea. It's seldom harmful, though molds and mold spores can have unpleasant effects and insects are always distasteful. The main reason to avoid using stale, musty or rancid flour is that its unpleasant smell is almost always accompanied by unpleasant flavors as well. This carries through in your baking, and will spoil the taste of all but the most robustly flavored baked goods.
The Question of Storage
The qualities of your storage area have a lot to do with your flour's storage life. If you live in a hot and humid climate, your flour will have a shorter shelf life. That's also the case if your pantry or cellar is damp, moldy or subject to severe fluctuations in temperature. For example, if you live in an area with hot summers and cold winters, your unheated garage is not an ideal year-round storage spot for your flour. The best storage locations provide an even, moderate temperature, are shielded from direct light, and have good ventilation to prevent the buildup of mold spores or stale smells.
Helping Your Cause
If you find that your flour often develops unpleasant flavors -- either because you bake infrequently, or because you're an enthusiast and keep dozens of flours on hand -- you can help prolong its shelf life in several ways. First, if humidity or flavor absorption is a problem, keep your flour in airtight packaging. This might be a commercial bin, a food-safe plastic bucket, or even a simple poly bag in which to place the flour sack. Another excellent way to prolong the life of your flour, especially in variable or humid climates, is to store it in a secondary refrigerator or freezer. Remove small amounts periodically as needed, and keep the rest well-wrapped in cold storage.
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