I've made my first attempt at cooking moules frites however I'm a bit disappointed with the results.

The batch of mussels were purchased from an online fishmonger specialising in Cornish seafood in the UK. Two thirds of the batch had already opened so following advice online I discarded them. The remaining ones I thoroughly washed in cold running water and removed any beards visible. On cooking, they all opened however they all tasted gritty and in the shells I could see black sludge.

Have I done something wrong? Is there an additional preparation step I missed? Or is it a bad batch?

Any help or advice is much appreciated. I haven't cooked fresh mussels before so it's a bit of a learning experience for me!

  • 5
    I was under the impression that, as long as open mussels close when you tap on them, they're perfectly fine to cook and eat, so you likely threw away many perfectly fine mussels. If they're dead, they won't close again, and should be discarded. Regardless, you seem to have followed all of the steps... did you scrub them or just wash them?
    – Catija
    Commented May 2, 2015 at 22:04
  • Research where the mussels originate from, there are disctinct sources, spanish mussels and fremch mussels, atlantic and mediterranean, they have different farming conditions and different reputations. Commented May 3, 2015 at 9:19

1 Answer 1


With regards to the grit, if they aren't farmed mussels (which generally are fairly clean) you may want to give them a soak for a while. This will give them the chance to expel any further sand/grid they may contain. There are varying theories of whether to use tap water, salt water, sea water or various other concoctions. And admittedly there are those who say any form of soaking will do all sorts of harm to the flavour. But if the alternative is disappointing gritty mussels, why not give it a try.

And as always, ask your fishmonger for advice. They will know the origin of the product, and whether or not you need to take extra steps in preparing them.

As for discarding opened mussels, don't just discard them when they seem open on arrival. If the shell is not cracked, give them a light tap (on the counter or with a knife) and see whether or not they will close in response. If they close in response, they are fine. If they don't close or tell you to stop it, then discard them.

And if two thirds of the batch really are dead ... I personally would not necessarily trust the other third to be in great shape.

  • 2
    Great answer, just to add, here's a great Serious Eats article that touches on these same points as a source, including information on soaking wild-caught mussels.
    – Catija
    Commented May 2, 2015 at 22:11
  • I've heard that they will eat flour and help clean themselves: cookstr.com/recipes/… one to add to the "various concoctions" list.
    – Mateo
    Commented May 3, 2015 at 3:57

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