Causes, Storage Tips & When to Throw Them Away

One of the questions we're asked most often is: "My mushrooms feel slimy. Are they still safe to eat?" The short answer? It depends. 

Mushrooms are naturally made up of around 90% water, so a little moisture is completely normal. But when that moisture builds up, or the mushrooms have simply been sitting around for too long, they begin to break down. This results in the sticky, slippery texture we all recognise as slime.

The good news? Understanding why mushrooms turn slimy can help you reduce food waste, store them better, and know exactly when it's time to cook them or compost them.

Why Do Mushrooms Become Slimy?

Fresh mushrooms are living organisms. Even after they're harvested, they continue to breathe, releasing moisture into their surroundings. When that moisture can't escape, it collects on the surface, creating the perfect environment for the mushrooms to soften and eventually spoil.

Is a Little Moisture Normal?

Yes! Fresh mushrooms can sometimes feel slightly damp, especially after refrigeration. That's very different from a thick, sticky coating. Here's a simple guide:

Not All Slime Is a Bad Sign

Before you throw out every mushroom that feels slippery, there's one important exception. Some mushroom varieties are naturally slimy or gelatinous, even when they're perfectly fresh.

Take Nameko mushrooms, for example. They're known for their glossy caps and naturally sticky coating, which becomes even more pronounced when cooked. It's this unique texture that makes them a favourite in Japanese cuisine, where they're often added to miso soups, noodle dishes, and hot pots to gently thicken the broth.

Similarly, fresh mushrooms can sometimes feel slightly damp from natural moisture released during storage, this isn't the same as spoilage. The difference lies in how the mushroom looks, smells, and feels overall. 

They're good to use if:

Signs of spoilage are :

• Thick, sticky slime across mushrooms that aren't naturally slimy

• Mushy or collapsing texture

• Sour or unpleasant smell

• Visible mould or significant discolouration

If you're ever unsure, remember: texture alone doesn't tell the whole story. Always consider the mushroom's smell, firmness, and the variety you're working with.

How to Keep Mushrooms Fresh for Longer

A few simple habits can dramatically extend your mushrooms' shelf life.

Store them in paper, not plastic

Paper bags or their original packaging allow moisture to escape while keeping mushrooms cool.

Wait to wash them

Only rinse mushrooms just before cooking. Washing them in advance adds unnecessary moisture and speeds up spoilage.

Keep them cool

Store mushrooms in the refrigerator and avoid leaving them out on the counter for extended periods.

Use them while they're fresh

Most fresh mushrooms are best enjoyed within 5–7 days of harvest.

Can You Still Cook Slightly Slimy Mushrooms?

If your mushrooms have only a small amount of surface moisture but still feel firm and smell fresh, they're usually still perfectly fine to cook. However, if they're sticky, mushy, or have developed an unpleasant odour, it's best to compost them and start with a fresh batch.

If you don't cook mushrooms regularly, dried mushrooms are a fantastic alternative.

They're shelf-stable, packed with flavour, and simply need a soak before cooking. Plus, they make it easy to enjoy gourmet mushrooms without worrying about freshness.

TLDR : Mushrooms turning slimy is simply part of their natural life cycle. The key is knowing the difference between a little moisture and true spoilage. Store them well, cook them while they're fresh, and you'll enjoy better flavour, texture, and less food waste.

Looking for more mushroom care tips? Read our guide to Shopping, Cleaning & Storing Mushrooms, or explore our collection of fresh and dried mushrooms to keep your pantry well-stocked.

Frequently Asked Questions

Why do mushrooms turn slimy?

Mushrooms become slimy when excess moisture builds up during storage or as they naturally begin to spoil.

Can you eat slightly slimy mushrooms?

If they're still firm, smell earthy, and only have a little surface moisture, they're often still safe to cook. Mushrooms that are sticky, mushy, or sour-smelling should be discarded.

How do you stop mushrooms from becoming slimy?

 Store them in their original packaging or a paper bag in the refrigerator, avoid washing them until you're ready to cook, and use them within a week.

How long do mushrooms stay fresh?

Most fresh mushrooms last 5 to 7 days in the refrigerator when stored correctly.

Why are my mushrooms slimy in the packet?

Condensation can build up inside packaging, especially if mushrooms experience temperature changes. If they remain firm and smell fresh, they're often still usable, but persistent slime is a sign they're beginning to spoil.