What is the storage life of flour?
All-purpose flour (white) in cabinet storage will have a shelf life up to 8 months if properly stored in a sealed container or if tightly wrapped, and for refrigerator storage, up to one year.
Freshly ground whole wheat flour, if stored at room temperature with plenty of access to oxygen will, after a few weeks or months, goes rancid. That rancidity is caused by the oxidation and breakdown of the oils in the wheat. Any flour milled from whole grains contains the germs. These are rich in oils (which is one of the benefits of freshly ground flour) and are prone to oxidation or – more commonly – going rancid. Depending on a few factors you can expect a storage life of 4 to 6 weeks.
Don’t try to store unprotected flours longer than a year. Hermetically sealed (for example: Mylar bag) in the absence of oxygen, plan on a storage life of 5 years at a stable temperature of 70 degrees F. They should keep proportionately longer if stored at cooler temperatures.
For optimum shelf life of flour, procure and store the whole grain itself (wheat berries) and do not grind the flour until you need it. Of course you will need a grain mill for this. Whole grain does not lose nutritional value in storage, whereas once ground into flour, the nutrient level begins to drop dramatically. Whole grains will store for decades in an oxygen free environment.
Mylar bags
Use Mylar bags and oxygen absorbers for an oxygen free environment. Air contains about 78% nitrogen and 21% oxygen, leaving about 1% for the other gasses. If the oxygen is absorbed (with the oxygen absorbers in a sealed Mylar bag), what remains is 99% pure nitrogen in a partial vacuum. Perfect for long term food storage.
Mylar bags do not need to be stored in food-grade buckets. The Mylar bags themselves are the barrier between the food and the outside environment, so long as they are sealed. You could leave the Mylar bags in the basement with no buckets, however I would not put them directly on a concrete floor (use a board or shelves) to avoid the potential of condensation due to the temperature difference between the cold floor and the air (even though most of the air is removed – it’s still a risk). Also, a bucket will serve as protection from the bag becoming punctured, especially from curious rodents.
Note that any sealable bag will work (seal-a-meal type vacuum sealer machines), as long as it holds a vacuum.