How Can You Tell If Nuts Have Gone Bad (Rancid)?

Because nuts are high in fat, spoilage most often takes the form of rancidity. This is a chemical change, different from mold or insect damage. Rancid nuts usually still look normal; the main changes are in their smell and taste. The second risk is mold and insect damage. In nuts such as pistachios and peanuts, mold that develops in damp storage conditions can pose a more serious health risk than mold on other nuts. Dust or holes on the shell can also indicate insects. Why Do Nuts Spoil Differently from Other Foods? Nuts such as walnuts, hazelnuts, and almonds are high in fat. Over time, exposure to air and light causes the fat to oxidize and turn rancid. As a result, the main spoilage in nuts is often a gradual change in taste and smell rather than mold. Nuts in their shells turn rancid much more slowly than shelled nuts because the shell protects the fat from exposure to air. Ground or sliced nuts spoil fastest because more of their surface is exposed to air. How Can You Tell If Nuts Are Rancid? Rancid nuts have a bitter taste with a slight paint-like or soapy note; it becomes more noticeable on the palate a few seconds after chewing. Their smell changes too: the mild, sweet, oily scent of fresh nuts gives way to a sharp, waxy odor. These signs may appear even when there is no visible change, so to check for rancidity you can smell and taste one small nut. Discard any nuts with mold, holes, or dust without tasting them, though; taste only reveals rancidity and tells you nothing about toxins produced by mold. Which Nuts Have a Higher Mold Risk? Some types of mold that develop on pistachios, peanuts, and walnuts in damp conditions should be taken more seriously than mold on other foods; these molds may produce harmful substances even when they cannot be seen. The safest approach for a nut with a black, green, or white fuzzy spot is to discard it without chewing it. If the other nuts came from the same container as a moldy nut, check them too and set aside the entire suspect batch before consuming any of it. This advice applies even if the moldy smell is faint. How Can You Spot Insect Damage? In nuts still in their shells, insect damage usually appears as a small hole in the shell—the point where the insect emerged. When such a nut is cracked open, it is usually hollow or dusty inside. In nuts without their shells, fine dust collected at the bottom and small moving specks indicate the same problem. If you notice such signs, inspect the entire batch in the same container, not only the visibly affected nuts; larvae may have spread to neighboring nuts unnoticed. How Can You Slow Rancidity? To slow rancidity, store nuts in a cool, dark place in an airtight container. Nuts left in an open bowl at room temperature may turn rancid within a few weeks. Refrigeration or freezing slows this process considerably, especially during hot weather. Dividing a large quantity into small portions and freezing them lets you thaw only what you need and minimizes the remaining nuts' exposure to air. Buying nuts in their shells is also a practical option if you want them to stay fresh as long as possible.