Darkening has more than one cause
UC Davis describes brown patches after rough handling and darkening of stalks and gills during drying in Agaricus mushrooms. It also discusses bacterial blotch and decay. Thus a dark area is not automatically mold, but neither is it proof of harmless bruising. A photograph or a color description cannot establish the cause in a particular package. [1]
Use storage history and the whole condition
Utah State Extension recommends choosing firm, unblemished mushrooms without mold and keeping them refrigerated, with breathable packaging after opening. Do not treat trimming off a spot as a validated way to make spoiled mushrooms safe. If the mushrooms have visible mold, are slimy or otherwise clearly deteriorated, discard them rather than using an internet image match to justify eating them. Uncertain storage history also matters. [2]
A hypothetical package comparison
Consider a fresh package with a documented handling bruise and an older package with spreading discoloration and loss of firmness. Calling both “black spots” removes information needed to judge their condition. The sensible inspection considers the whole package and its history; it cannot promise safety from the appearance of a single spot. [1][2]
| Finding | Interpretation |
|---|---|
| Localized dark patch | May have several causes |
| Visible mold or marked deterioration | Do not use as food |
| Normal-looking surface | Not a laboratory test for safety |
Sources for this article
- UC Davis — Mushroom produce fact sheet (2002)
Source consulted: 2026-09-20. This is a reference resource, not a claim that we conducted the studies or tested a product. - Fruit and Vegetable Guide Series: Mushrooms | USU
Source consulted: 2026-09-20. This is a reference resource, not a claim that we conducted the studies or tested a product.