A quarter cup of walnuts offers around 15 per cent of your daily tryptophan, around 20 per cent of your daily copper, over 40 per cent of your daily manganese and a whopping 94.6 per cent of your daily omega 3 fatty acids, according to WHFoods.com. With proper care, you can keep your shelled walnuts for up to six months in the refrigerator and a full year in the freezer. If you leave them at room temperature or in the refrigerator for too long, however, they can become rancid.
Examine the walnuts closely and squeeze them gently. Healthy, fresh walnuts should be hard when you squeeze them. They should not look wrinkled, withered or otherwise old.
Smell the walnuts. If they have even a faintly bad or strange smell, they have probably become rancid, and you should not eat them. This smell might be similar to fish or even paint thinner. If they do not have a clear smell or only smell like walnuts, they are almost certainly not rancid.
Nibble a tiny piece of one of the walnuts. Some walnuts are naturally slightly bitter, but rancid walnuts have a distinctively bitter flavour. If your walnut tastes bad, spit it out and discard the rest of the batch, as they are probably all spoiled.
Considering your walnuts' age and storage can help you determine how likely they are to be rancid. If you have only had them for a few weeks and have kept them in an airtight container in the refrigerator for that time, they will almost certainly be fresh. If, however, you have left an open package of walnuts at room temperature for a month, rancidity is significantly more likely.