Mushrooms are highly perishable and go bad relatively quickly. They possess a naturally high water content, often exceeding 90%, making them susceptible to rapid deterioration after harvest. This high moisture, combined with a high respiration rate, creates an environment where spoilage microorganisms thrive, leading to a short shelf life. Their delicate structure also makes them prone to physical and enzymatic breakdown, accelerating the loss of freshness.
How to Tell If Mushrooms Have Spoiled
The most noticeable sign of spoilage is a sticky or slimy film developing on the cap and stem. Fresh mushrooms should feel firm and dry to the touch, but as they age, the breakdown of cell walls releases moisture, which combines with microbial growth to create a slick, mucilaginous coating. This sliminess is a clear indication that the fungi should be discarded, as it suggests bacterial proliferation.
Visual cues also provide strong evidence of deterioration, including the appearance of dark spots or an overall darkening of the surface color. While some discoloration can be due to oxidation, excessive browning or the presence of fuzzy, discolored patches of mold means the fungi are no longer safe to consume. Additionally, a loss of firmness, where the mushroom becomes soft, spongy, or shriveled, shows that dehydration and structural decay have progressed significantly.
The sense of smell is another reliable indicator, as fresh mushrooms typically have a mild, earthy aroma. If the fungi have spoiled, they will often emit a strong, unpleasant odor that can be sour, fishy, or distinctly ammonia-like. This foul smell is a byproduct of spoilage bacteria and is a definitive sign that the mushrooms should be thrown away.
Shelf Life and Spoilage Factors
Common varieties like white button and cremini mushrooms generally maintain quality for about four to seven days under optimal refrigeration. Some whole mushrooms may last up to ten days, but this range depends heavily on how they are handled and stored. The short shelf life is primarily due to the fungi’s high respiration rate, meaning they continue to “breathe” and break down stored carbohydrates quickly even after being picked.
Several factors accelerate this natural spoilage process, with moisture being the most significant contributor. Excess humidity or condensation on the surface of the mushroom encourages the rapid growth of the bacteria that cause sliminess. Temperature fluctuations, such as those experienced during transport or when repeatedly moving the fungi in and out of the refrigerator, also hasten enzymatic browning and decay.
Physical damage, such as bruising or slicing, reduces the shelf life by exposing more surface area to oxygen and microbial contamination. Sliced mushrooms, for example, typically spoil faster than whole ones, often lasting only four to five days even when refrigerated. The increased surface area allows for greater water loss and provides more entry points for spoilage organisms.
Best Practices for Keeping Mushrooms Fresh
To maximize freshness, proper storage focuses on controlling moisture and allowing the fungi to breathe. The most effective method is to store them in a brown paper bag, which absorbs the excess moisture that the mushrooms naturally release during respiration. The open top of the bag allows for air circulation, preventing the buildup of humidity that leads to a slimy texture.
Avoid storing mushrooms in airtight plastic bags or sealed containers, as these trap moisture and carbon dioxide, accelerating decay. The ideal location in the refrigerator is on a main shelf, rather than in the high-humidity crisper drawer, which can also promote sliminess. Additionally, mushrooms should be kept away from strong-smelling foods, as their porous structure can easily absorb surrounding odors.
Delay washing the mushrooms until the moment they are ready to be used. Because they are highly absorbent, washing them prematurely causes them to soak up water, which significantly increases the surface moisture and drastically shortens their remaining shelf life. Keeping them dry until use helps preserve their firm texture and flavor.