THE FIX: That smell is rancid flour. Light and heat speed up the decay of flour, and it’s faster yet in whole-grain varieties. The reason: The higher fat content (from the oil in the grain) makes these flours more susceptible to spoilage. Always store them in airtight containers in the refrigerator or freezer, and bring them back to room temperature before using them. Refined flours that have been stripped of the bran and germ (all-purpose, cake, pastry, and bread) are more stable and can be stored in a cool, dry place (no warmer than 75°).