Rancid flour is peculiar in that the extent of its spoilage is most pronounced after it's cooked. Rolls made with expired flour taste and smell like modeling clay. Sauces may adopt the flavor of sour milk. Determining whether you have rancid flour is as simple as trusting your senses. Perform a simple sniff test if you believe your flour has gone bad.
How to Spot Sour Flour
Flours are made from ground-up grains. The fat in these grains breaks down over time as it's exposed to elements, namely air but also bacteria. Rancid flour has a uniquely sour smell, similar to that of a dank, moldy basement. Dispose of or compost rancid flour, or use it to make glue or modeling dough.
Most home bakers rely on all-purpose flour to make bread, rolls and cookies. All-purpose flour is made by grinding a wheat kernel's starchy endosperm. It has an average shelf life of six to eight months, but it's usable for six to eight months beyond its expiration date if you store it properly. Airtight, cold storage in your fridge or freezer is best for all flours, as this prevents heat and air damage and keeps out pests.