How to Tell If Mushrooms Have Spoiled: Can You Trim a Suspect Part?

The most reliable way to tell whether mushrooms have spoiled is to check whether their surface has become slimy and to smell them. Fresh mushrooms have a mild, earthy smell, while spoiled mushrooms give off a sour or sharp, ammonia-like odor. Eating spoiled mushrooms can cause food poisoning, so the safest choice is to discard an entire mushroom that is noticeably slimy or smells bad instead of cutting off part and using the rest. This check can also be done right after shopping; if a mushroom in the package already looks suspicious, it may be a sign that the others will spoil soon as well. What are the visual signs of spoilage? A fresh mushroom's surface is dry and slightly dull, while a mushroom starting to spoil develops a wet, slimy layer. This layer is more noticeable underneath the cap and on cut surfaces. The mushroom's color also changes over time; dark brown or nearly black spots on light-colored mushrooms are another sign that spoilage is progressing. Stems that shrink and become thin, and cap edges that curl inward, are also visual signs that a mushroom is no longer fresh. What does the smell tell you? A fresh mushroom has a mild, earthy, neutral smell; if this changes over time to a sour or sharp, ammonia-like smell, the mushroom has spoiled. Changes in smell usually appear before visual signs. Excess moisture collected inside the package can also be a warning sign of bad odors; if the inside of the bag is fogged and wet, most of the mushrooms may start to spoil soon. When checking the smell, slightly opening the package and smelling directly from the top is the most reliable way to detect it clearly. Can partially spoiled mushrooms be sorted out? If only 1 or 2 mushrooms have softened slightly and the overall smell is still normal, removing those pieces and using the rest is a reasonable approach. However, if slime or a bad odor has spread through the entire package, removing a few pieces is not enough. In this case, mold growth or bacteria may generally have spread over a much wider area than is visible; for this reason, discarding the entire package when there is a suspicious odor is safer than trying to salvage a few mushrooms. If in doubt, cooking the mushrooms and checking their smell again is not an option; cooking does not eliminate the risk caused by spoilage. This is because mushrooms have a spongy, porous texture; this structure can carry moisture and microorganisms much deeper than the surface, beyond what is visible. In a firm-skinned vegetable, spoilage generally remains limited to that area, whereas the same boundary cannot be determined as reliably in a mushroom. How should mushrooms be stored to delay spoilage? Mushrooms stay fresh much longer when stored in a paper bag or a ventilated container instead of a plastic bag; plastic retains moisture and speeds up sliminess. Storing them before washing also reduces moisture buildup. Mushrooms should be stored on the middle shelf of the refrigerator, away from other foods with strong odors; because mushrooms readily absorb odors, this helps preserve both their freshness and flavor. Properly stored fresh mushrooms generally keep well for about 1 week; cut or sliced mushrooms keep for a much shorter time. If the original packaging of store-bought mushrooms is perforated, leaving them in that package may be more practical than taking extra measures. Lining the container with a paper towel prevents the mushrooms' own moisture from collecting at the bottom and may extend shelf life by a few more days. Quick summary The formula for telling whether mushrooms have spoiled is to check their smell and texture: if the surface is slimy and there is a sharp odor, the mushrooms should be discarded. Storing them dry in a paper bag is the most effective way to delay this problem.