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Why do nuts turn rotten?

Walnuts, almonds, pistachios…we love them and store them at home. But if they are in large quantities, storing becomes a problem as they turn rancid. And that they have gone rancid cannot be told by the smell, one has to taste to find out!

According to science, the speed with which nuts turn rancid is in direct proportion to the amount of polyunsaturated fatty acid they contain. Fastest to slowest to turn rancid, in order: walnuts, pistachios, peanuts, almonds, cashewnuts. Unshelled nuts, protected by nature’s armour, will keep for a year or even two, especially if refrigerated. So if your nuts were fresh to begin with - that is, bought from a reputable supplier - their shells might keep them fresh for a year if they are stored in a cool place. Shelled nuts, especially those that have been chopped or roasted, are more prone to rancidity. Secured in an airtight container, they can be stored for four or five months in the refrigerator and for up to a year in the freezer. Cashewnuts are an exception. They are never sold in their shells as the shells are toxic. Cashewnuts are available with the skin on. These are better for storage. 

How can you tell if a nut is rancid? If you are shopping in a store, ask for a sample if possible. Smell is not reliable; taste is the best test. If it tastes sour or rank, shop somewhere else.