A. Nicola McKeown, PhD, director of the nutritional epidemiology program at Tufts’ Friedman School and a scientific advisor to the Whole Grains Council, answers: “Yes, whole-wheat flour will go bad sooner than all-purpose flour. This is due to the fact that whole-wheat flour has a higher oil content because it retains the inner germ and outer bran layers. Exposure to air causes the oil in flour to degrade over time, causing the flour to develop a rancid smell. Given this, it is important to consider two things when purchasing flour – the size of the bag you should purchase and how you plan to store it.
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“Flour generally is sold in two- and five-pound bags. If you live alone or don’t bake very often, choose the smaller bag. For best storage practices, choose a cool, dry cupboard to store your flour in, and store it in an air-tight container. The Whole Grains Council says that if stored properly in airtight containers, most whole-grain flours will keep for one to three months on a cool, dry pantry shelf, or two to six months in the freezer. All-purpose flour, on the other hand, can last for 8 to 12 months if stored properly.
“All flours are susceptible to bugs (‘weevils’), so always look at your flour to make sure it’s not a home to these small critters. The bottom line is: If it smells bad or contains small bugs, then discard it!”