For most people, the problem only becomes apparent when the flour is used. An unpleasant smell or a bitter taste can be signs that the fat in the flour has turned rancid.
According to researcher Shiori Koga from the food research institute Nofima, this occurs especially in wholegrain flour, where the outer layers of the grain are still present.
Some people also discover insects in their flour. Simon Ballance from Nofima explains that this is typically due to improper storage.
Flour should be kept dry, dark, and in sealed packaging to avoid such problems.
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The date often causes confusion
Many believe that “best before” means the flour must not be used after that date. This is not the case.
According to the Danish Veterinary and Food Administration, the labeling relates to quality rather than food safety for dry products such as flour.
Ballance points out that flour can often be used long after the date if it has been stored correctly.
In such cases, it is recommended to rely on the senses and assess appearance, smell, and taste.
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Processing makes the difference
Shelf life depends on the type of flour. Sifted wheat flour contains almost no fat and therefore keeps longer than wholemeal flour, explains Shiori Koga.
Oats have a higher fat content and are heat-treated to extend shelf life.
When grain is milled into flour, the surface area increases, and quality deteriorates more quickly. Only when moisture and mold develop does the flour become harmful to health.
Until then, it is primarily a matter of quality.
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Sources: Forskning.no, and the Danish Veterinary and Food Administration.