Whole Wheat Flour Goes Rancid Faster Than White
White flour is milled from the starchy endosperm alone, with the oil-rich germ and bran removed, so it stays stable at room temperature for months. Whole wheat flour keeps the germ, which contains natural oils that oxidize and turn rancid within a few months at room temperature — you'll notice a slightly bitter, "paint-like" smell when it's gone off. Store whole wheat and other whole-grain flours in the freezer or fridge if you don't go through them quickly; white flour is fine in a sealed container in the pantry.
Sources & methodology: These tips draw on established food-science references —
Harold McGee's food-science writing, America's Test Kitchen /
Cook's Illustrated testing, Serious Eats'
technique reporting, USDA food safety guidance,
and peer-reviewed food-safety research (including UC Davis
cutting-board studies) — not reworded recipe-blog consensus.