In short: Mushrooms are bad if they are slimy, smell foul, show dark spots or browning, or feel soft and shriveled. Refrigerated mushrooms last 5–7 days; at room temperature, only 1–3 days. If you are unsure, throw them out.
How do mushrooms get slimy?
Mushrooms are very high in water—about 90% of their weight is moisture. When bacteria and other tiny germs grow on the surface, they break down the mushroom's firm cells, and the mushroom becomes soft and slippery. A slimy or wet, slippery surface is one of the clearest signs that a mushroom is bad and not safe to eat.
What does a spoiled mushroom smell like?
Fresh, good mushrooms have an earthy, neutral smell. If a mushroom has gone bad, it will develop a foul odor—something sour, tangy, or unpleasant. This smell means fermentation or decay is happening inside. If you open the container and get a bad whiff, those mushrooms should go straight to the compost.
What color changes mean it's time to throw them out?
Fresh mushrooms are usually pale cream, white, or light brown. As they age, they may get slightly darker or develop dark brown spots or black marks on the surface—this is a sign that the mushroom flesh is decaying underneath. If the browning comes with sliminess, a bad smell, or softness, the mushroom is definitely spoiled.
When do mushrooms feel soft instead of firm?
A fresh mushroom is firm and holds its shape. Over time, mushrooms lose moisture and their cells collapse. A soft, shriveled, or floppy mushroom is past its prime and should not be eaten. Press gently on a fresh mushroom—it should feel springy and solid, not mushy or soggy.
How long do fresh mushrooms actually last?
Refrigerated mushrooms stay good for about 5–7 days. At room temperature (on a kitchen counter), they spoil much faster—in just 1–3 days. This is why storing mushrooms in the fridge is so important. Keep them in a paper bag or a container where air can flow around them, not in a sealed plastic bag.
The four-sign spoilage checklist
Before you cook with mushrooms, do a quick check:
- Texture: Is it slimy or slippery? Throw it out.
- Smell: Does it smell foul or sour? Throw it out.
- Color: Are there dark spots, browning, or black marks? (Especially if they come with other signs.) Throw it out.
- Shape: Does it feel soft, shriveled, or floppy? Throw it out.
If any one of these is true, compost the mushroom. If you are unsure, when in doubt, throw it out—food safety matters more than saving a single mushroom.
Why cooking mushrooms matters
Always cook mushrooms before eating them. Cooking kills harmful germs and makes mushrooms safer and easier to digest. Never eat raw mushrooms straight from the container.
Safety first: Always ask a grown-up before cooking or eating mushrooms. Never pick or eat wild mushrooms, even if they look delicious or a friend says they know which ones are safe. Wild mushrooms look like safe species so closely that even experts can make deadly mistakes. The safe way to enjoy wild fungi is to look at them with your eyes only. The best mushrooms for eating are ones you grow in a kit with an adult, or ones from a trusted food shop.
The short version
Mushrooms go bad when they become slimy, foul-smelling, discolored, or soft and shriveled. A mushroom in the fridge lasts about a week; at room temperature, only a few days. Cook all mushrooms thoroughly before eating. When in doubt, throw it out—and always grow or buy your mushrooms safely, with a grown-up by your side.
Curious questions
Can you eat a mushroom with small dark spots?
If the spots are only surface spots and the mushroom is firm and smells fresh, you can cut them away. But if dark spots come with sliminess, a bad smell, or soft spots, the whole mushroom should be thrown out.
How long do mushrooms last in the fridge?
Refrigerated mushrooms stay fresh for about 5–7 days. At room temperature, they spoil in just 1–3 days, so keep them cold.
What is the 'when in doubt, throw it out' rule?
It means if you are not sure whether a mushroom is safe to eat, it is better to throw it away than to risk getting sick. Food safety is more important than saving a single mushroom.
Why do mushrooms get slimy?
Mushrooms are 90% water. When bacteria grow on the surface, they break down the firm cells, making the mushroom soft and slippery. Sliminess means spoilage has begun.
Should you ever eat raw mushrooms?
No. Always cook mushrooms before eating them. Cooking kills harmful germs and makes them safer to eat.
Sources & further reading
- PMC/NIH — Microbial contamination and microbiome composition of fresh edible mushrooms: a critical review
- University of New Hampshire Extension — Boosting the Quality and Safety of Specialty Mushrooms
- UC ANR — Food Safety Tips for Mushrooms
A note for growers: only grow and eat mushrooms from our kits or from species you know are safe, and always check with an adult. Never eat a wild mushroom unless an expert adult says it’s safe.
