To maintain their optimal protein content, it is best to store flour in the freezer (let it equalize to room tempature prior to baking) and refrigeration can work too. The main reason we keep our flour refrigerated is to slow the oxidation process, which makes flour behave differently and can lead to the oil in the germ becoming rancid. I've heard from several bakers that they can tell from how the flour behaves whether it's six months old or six hours old. The gold standard is to grind just as much flour as you need and use it immediately, but we know that's not always feasible.

Freezing flour is an excellent option. If it's frozen in an air-tight container, like a plastic bag, it can remain stable indefinitely, since the oxidation process is effectively stopped. Freezing doesn't seem to do any damage to the flour.

The reason why to refrigerate our flour, when you can keep "regular" store-bought flour in the pantry for months with no ill effects. Conventional flour is shelf-stable because it's been processed to remove the germ (a source of many nutrients) and the bran (a great source of fiber), leaving only the starchy endosperm. Additionally, this flour is usually bleached, which whitens the color of the flour and makes it "softer." Finally, shelf-stable versions of some of the nutrients that were removed are mixed back into the flour as additives to make it "enriched." These additives can affect the flour's texture, gluten development, and taste.

Our flour, in contrast, is made with the whole grain (germ, bran, and endosperm), so all the nutrients are kept intact.