Nuts are not only a delicious snack, they're also full of protein, healthy fats, vitamins, antioxidants and minerals. Although nuts are high in oil, it's the healthier, unsaturated kind. The bad news is nuts can turn rancid because the unsaturated oils oxidize quickly during exposure to light, heat and air. Nuts that can more easily turn rancid are listed in order of fastest to slowest: walnuts, pecans, Brazil nuts, peanuts, almonds, pistachios, cashews and hazelnuts, according to The Washington Post.
Taste one of the nuts. Ask if you can sample a nut if you're in a store and the nuts are sold loose in a bin. If the nut tastes sour or bitter, it has become rancid.
Smell the nut to learn if it's still fresh. Rancid nuts have an unpleasant fishy odor.
Visually inspect the nuts. Nuts that have darkened in color is a sure sign they've turned rancid. Check that the nuts haven't become shriveled, dry or moldy in appearance.
Purchase nuts from a reputable food store that has a high turnover of their products.