Like all things with a fairly high fat content, nuts are prone to going rancid. Rancidity isn’t life threatening, and spoiled nuts won’t make you sick, but they do taste bad—and feel bad—in your mouth. (And I want nuts to taste and feel good in my mouth.)
Luckily, keeping nuts from going rancid is pretty easy: You just have to keep them cool. Nuts are full of unsaturated fats, which are more prone to spoiling than saturated fats (like lard and butter). Nuts will obviously be alright at room temperature for a few days, but warmer temperatures will eventually cause them to soften and develop sour, plasticky, or moldy flavors and aromas.
Keeping them in the fridge (or freezer) stabilizes these fats to keep them from going rancid. (It also has the added benefit of keeping pests, such as pantry moths, out of your nuts.) This is particularly helpful for nuts with high fat contents, like macadamia nuts, brazil nuts, pine nuts, pecans, and cashews, which are (obviously) more likely to go rancid before nuts with lower fat contents like walnuts, almonds, and pistachios. (These can still go rancid, of course, it will just take a little longer.)
Keep those nuts cold
To keep your nuts tasting and feeling fresh, store them in the fridge or freezer. The fridge is the best place for a small to moderate amount of nuts, or the amount you can see yourself consuming in a four-to-six-month period, which is how long they’ll stay fresh for when refrigerated in a sealed container. If you find yourself with a windfall of nuts, keep as many as you can in their original packaging, and store them in the fridge. (Only if the packaging is sealable, however. If the packaging is something like a flimsy, bulk-bin bag, transfer it to something air-tight and sealable.) The nuts will also stay fresh in the freezer for up to a year—when your fridge supply runs out, just refill it from the freezer, until you are out of nuts, frozen or otherwise.
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