Bad tasting mussels and avoiding buying them Sometimes when you buy mussels, you find that they taste sort of rancid or at least not very fresh, even if they are alive (or at least closed). 

How can the taste get so bad if they still are alive? And how can you tell at the supermarket or fish monger?
Always check that most of the mussels are alive when you buy them.

Check that the shells are not broken, and that they are wet.

At your house, throw away all the dead mussels and process as soon as possible. 

Cook (steam) as fast and as furious as you can for no more than two minutes. At that point, the mussels should have opened and nearly done.

Overcooking can produce a rubbery texture and spoil the taste.