Even if you don’t bake all that much, you probably have a bag of flour in your pantry. Beyond bread and other baked goods, the processed wheat powder is used as a breading and thickening agent in a wide variety of cuisines. It’s obviously shelf-stable—which is why we keep it on the shelves of our pantries—but just how stable is it, and how can you tell if it destabilizes?
The short answer is that flour is “good” for 3-8 months at room temperature and pressure, but that timeframe can be lengthened considerably with a few storage modifications. Storing it in the freezer, for example, can extend its lifespan by years, especially if you take care to seal it in an airtight container to prevent odors from creeping in. (Refrigerated flour can last up to a year, but I simply do not have room in my fridge.)
Some flours are more prone to going bad than others. White flour has the longest shelf-life due to how it’s processed. The grain and bran are stripped away, leaving only the starchy endosperm, and the grain and bran are where the oils live. Oils are good for you, but they also go rancid, so whole-wheat flour (or alt-flours made with other oily ingredients, like almonds) are likely to go bad more quickly than their high-processed counterpart.
In addition to oils that can go rancid, moisture is the main factor that accelerates flour’s demise, so keep it in an air-tight container no matter the storage temperature. Wet flour usually quickly turns into moldy flour, so take care not to dip any wet utensils or scoops into the bag.
If you’ve lost track of how long your flour has been sitting in your pantry, give it a peek—and a smell. Look for signs of mold and bugs, and sniff around for anything that smells “off.” Rancid oils have always smelled like crayons to me, but bad flour can also smell musty or sour. Flour doesn’t smell like much on its own, so if you find that your brain is “trying to place” an odor, then that odor does not belong. Toss the flour and buy a new bag. (It’s very cheap.)