Fresh portabella mushrooms last 4 to 7 days in the refrigerator, and they give off several clear signals when they’ve gone bad. Knowing what to look for (and smell for) can save you from an unpleasant meal or a stomach ache.
How They Look When They’ve Turned
The most obvious sign is slime. A sticky or slippery coating on the surface means bacteria are actively breaking the mushroom down. This isn’t a gray area: slimy portabellas should go straight into the compost.
Dark spots are trickier. Some bruising is normal, especially on portabellas, which are handled a lot between farm and store. But if you see many dark spots, large blackened areas, or patches that feel soft and mushy when pressed, that’s decomposition, not bruising. The flesh of a fresh portabella should feel uniformly firm. If it’s turned rubbery, soggy, or breaks apart easily, the internal structure has started collapsing.
Wrinkling is worth noting separately. A slightly wrinkled cap just means the mushroom has lost some moisture. It’s not dangerous, but the texture and flavor will be diminished. A severely shriveled portabella, on the other hand, is past the point of being enjoyable.
The Smell Test
Fresh portabellas have an earthy, slightly musky scent. When they spoil, the smell shifts dramatically. Sour, ammonia-like, or alcoholic odors all point to bacterial growth or fermentation happening inside the mushroom tissue. A fishy or putrid smell is an even stronger warning. If you catch any of these, toss the mushroom, even if it still looks passable. The nose is often ahead of the eyes when it comes to detecting spoilage.
White Fuzz: Mold or Something Harmless?
White fuzzy growth on a portabella can be confusing because mushrooms are fungi themselves. In many cases, that white fuzz is just mycelium, the mushroom’s own root-like network, continuing to grow. Mycelium is bright white, has a cottony or rope-like texture, and stays close to the surface.
Mold, by contrast, tends to be grayish rather than pure white, has extremely fine wispy strands, and often smells like mildew. It also grows fast. If you notice a small patch one day and it’s spread dramatically within 24 to 48 hours, that’s mold. Green, blue, or black fuzzy patches are always mold. When in doubt, the mildew smell is the giveaway.
How to Store Them So They Last
Moisture is the number one enemy of stored mushrooms. Plastic containers and sealed plastic bags trap humidity, creating the exact conditions that cause slime, discoloration, and mold. The best storage method, confirmed through side-by-side testing by The Kitchn, is a brown paper bag in the refrigerator. The paper absorbs excess moisture while still allowing airflow. You can line the bag with a paper towel for extra absorption.
Skip the crisper drawer. Most people leave their crisper set to high humidity, which is great for leafy greens but speeds up mushroom spoilage. A regular shelf in the fridge works better. Don’t wash portabellas before storing them. Rinse or wipe them down right before you plan to cook.
With proper storage, whole portabellas reliably last 4 to 7 days from purchase. Sliced portabellas degrade faster because more surface area is exposed to air and moisture.
Cooked Portabellas Last Longer
Leftover cooked portabellas keep for 7 to 10 days in the refrigerator, giving you a noticeably wider window than raw ones. That said, if they’re mixed into a dish with ingredients that spoil faster, like dairy or fresh greens, the dish’s shelf life drops to match the most perishable ingredient.
Why You Should Always Cook Portabellas
Beyond spoilage, there’s a separate reason to avoid eating portabellas raw. Like all mushrooms in the Agaricus family (which includes white button and cremini mushrooms), portabellas contain a naturally occurring compound called agaritine. Levels in fresh Agaricus mushrooms range from 80 to 1,730 mg per kilogram, varying by growth stage, the part of the mushroom, and whether it was cultivated or wild-harvested. Agaritine has raised some concern in toxicology research.
The good news: agaritine is unstable and breaks down readily with heat. All common cooking methods, including sautéing, grilling, roasting, and boiling, significantly reduce agaritine levels. This is one of the practical reasons food safety experts recommend cooking mushrooms rather than eating them raw, on top of the fact that cooking also makes their nutrients more accessible and their tough cell walls easier to digest.