Flour exposed to air, light, moisture, or insects tends to spoil. It’s just like any other dry food. If you leave a bag of flour in your cupboard, some problems might arise, causing the flour to spoil.
Mold
First of all, it can develop mold. Flour absorbs moisture and becomes moldy due to humidity or temperature variations. Mold growth and foul odors may develop in flour sacks if stored in a moist environment.
Before you see the mold, you’ll be able to smell it. The best-by date printed on the packet of flour sold in shops is a notably clue to know how safe-keep your flour stock.
If the flour looks and smells fine, you may still consume it beyond the expiration date. But I wouldn’t recommend it if you can’t tell the difference between bad and good flour. Go with what the best-before-date says in this case.
When sniffing the flour bin contents, it is easiest to identify rancidity in the flour. Any flour that has gone rancid will have a foul scent and may even have a different color and texture from regular flour.
Oxidation
This other factor you need to watch out for aside from mold. It happens when oxygen from the air reacts with the nutrients in flour, causing them to degrade.
It’s especially true for whole-grain flours, and that’s because it inherits oils in whole grains that will develop rancid due to oxidation.
Insects
The next possible problem to look out for is insects. Even if you keep your flour in airtight containers, insects like weevils or moths may find it.
There have also been reports of weevils, sometimes known as flour bugs, infesting flours, grains, and rice in the hands of certain homesteaders. When you buy flour, weevils are there because they were already in the bag when you purchased them.
Feminine weevils deposit their eggs in grain before being milled and further processed into flour or other products. The eggs may survive the field-to-table procedure and hatch in the sealed flour, providing the proper circumstances.
Because of the limited amount of processing involved with less refined grains and flours, there is a greater risk that they will include live weevils.
Depending on the environment, it might take weeks or months for them to hatch. However, after they hatch, you’ll have an infestation that’ll be difficult to eliminate.
Additionally, you need to know that flour acts like a sponge, absorbing the odors of anything around it.
So, if you have onions near your flour, chances are, the cake you’ll make with it will then have an oniony aroma. Similarly, flour, or any other food, is not stored near chemicals such as cleaning agents.