White flax seeds contain plant-based fats, which can go rancid over time if they are exposed to heat, light, or air. To keep them fresh, store the seeds in an airtight container in a cool, dry place, such as a pantry cupboard. Avoid keeping them near the stove, oven, or a sunny window, because heat and light speed up oxidation.
For longer storage, you can put the container in the refrigerator or freezer. This is especially helpful if you buy a large pack or live in a warm climate. When you take seeds out of the fridge or freezer, let them come to room temperature before opening the container to prevent condensation from forming. Condensation can introduce moisture, which may cause the seeds to become sticky or spoil.
Whole flax seeds generally stay fresh longer than ground flax, because the outer shell protects the oils inside. If you grind your own seeds, use the ground powder within a few days or store it in the fridge in a sealed container. Always check the smell before using – fresh flax seeds have a mild, nutty aroma. If they smell bitter or like old oil, they have probably gone rancid and should be discarded. Also check the best-before date on the package, but remember that proper storage can help the seeds keep their quality until that date.