Nuts such as walnuts, hazelnuts, and almonds stay fresh much longer in their shells than after they are shelled. The shell greatly reduces the surface exposed to air and slows the oil inside from becoming rancid. In-shell walnuts can last up to a year in a cool, dry place, while shelled walnuts may start to turn rancid within a few months at room temperature.
How should shelled nuts be stored?
Shelled nuts last noticeably longer when stored in an airtight container in the refrigerator. Freezing them extends their shelf life further, and they can remain close to fresh even after months. Shelled nuts left in an open container on the kitchen counter spoil the fastest because of exposure to light and heat. For high-fat nuts such as walnuts, the change may become noticeable within a few weeks.
How can you tell if a nut has turned rancid?
A rancid nut has a sharper, slightly paint-like smell compared with a fresh one, and leaves a faint burning or soapy taste on the tongue. Discard nuts with these signs because cooking does not reverse rancidity. When buying in-shell nuts, check that the shells have no cracks or holes. This can extend storage life and reduce the risk of pests; an intact shell provides the best protection for the kernel inside.
How should you plan storage for bulk purchases?
Instead of leaving nuts purchased by the kilogram in one large bag that is opened and closed repeatedly, divide them into smaller bags sized for a week's use and keep the rest in a cool place. Roasted nuts turn rancid faster than raw nuts because roasting makes the surface somewhat more porous. Refrigerating roasted nuts can therefore make a more noticeable difference than refrigerating raw nuts. Salted roasted nuts may last a little longer than unsalted ones because salt can somewhat delay moisture absorption. Even so, the difference is only a few weeks and does not replace proper storage. Some nuts, such as peanuts, turn rancid faster than others. Keeping them near the bottom of a mixed-nut container rather than at the top reduces their exposure to air when the top is opened frequently.
If you roast nuts, let them cool completely before putting them in a sealed container. Hot nuts can sweat inside a closed container, allowing moisture to build up and creating conditions for mold. If you frequently open and close a nut jar, check the lid gasket from time to time. A worn gasket may prevent the lid from closing tightly and allow air inside. When preparing a mixed-nut container, chopping the different types to a similar size can be helpful both for appearance and for keeping them fresh for a similar amount of time. Overall, storing nuts in or out of their shells is one of the most important factors affecting how long they stay fresh.