How Do You Tell If Mussels Have Gone Bad?

The most practical way to check whether mussels have gone bad is the shell test: before cooking, if a slightly open mussel doesn't close when you tap it, it has died and should be thrown away. Mussels with cracked or broken shells should be discarded the same way.

Which mussels should be discarded before cooking?

A live mussel's shell is either closed or slightly open; if you tap a slightly open one with your finger, the shell should close within a few seconds. A mussel that stays fully open and doesn't close when tapped may already be dead and starting to spoil, and should be thrown away uncooked.

Mussels with cracked or deeply broken shells should also be discarded, since bacteria can get in through the damage. Fresh mussels smell mild and briny, like the sea; a sharp fishy or ammonia-like smell is an early sign of spoilage.

What to check after cooking

The standard rule is that mussels whose shells stay closed during cooking shouldn't be eaten; there's a good chance those mussels were already dead or starting to spoil before cooking. The meat inside mussels that do open should look plump, moist and its natural colour.

If the cooked meat looks shrivelled, dried out or has turned greyish, the mussel's freshness before cooking is also questionable; in that case it's safer to throw it out without tasting it.

Storage and food safety

Fresh, live mussels should be stored in the fridge covered with a damp cloth for no more than 1 to 2 days; keeping them in an airtight container or straight in water suffocates and kills them, making them spoil faster. Cooked mussel leftovers should be eaten within 3 to 4 days from a sealed container in the fridge.

Eating spoiled or questionable mussels raises the risk of shellfish-related food poisoning; with mussels, discarding every doubtful one is the safer habit rather than assuming a slightly off one is still fine.

Do the same checks apply to frozen mussels?

The shell-tap test doesn't apply to frozen, shelled mussels; instead, check whether the package is sealed tightly and whether there are heavy ice crystals on the meat, a sign of freezer burn. If the meat looks greyish or has a sharp ammonia smell once the pack is opened, the mussels shouldn't be eaten even though they were frozen.

Frozen mussels shouldn't be refrozen once thawed, and should ideally be cooked the same day; leaving thawed mussels out at room temperature for a long stretch leads to the same rapid spoilage seen in live ones.

Checking whether the mussel bag has a harvest or packing date printed on it helps estimate how long they've been sitting around. If there's no date, cooking them the same day you buy them is the safest choice; planning to keep mussels for several days is risky from the outset.

Live mussels are better carried home in a paper or mesh bag rather than a sealed plastic one; the moisture and heat that build up in a closed plastic bag can stress and kill them before they even reach the kitchen.

It also helps to check whether mussels at the counter are sitting directly in ice rather than just on top of it; direct contact with ice helps them stay cold and fresh for longer. That detail gives an indirect clue about how carefully they were handled during transport and sale.