Put the mussels in a casserole with the wine and 100 ml water. Place over a high heat, bring to the boil and cook for a few minutes, stirring often, until all the mussels have opened.
Strain the cooking liquid through a fine sieve into a jug, leaving behind any grit.
Put the mussels in a large bowl with plenty of ice cubes and cover with cold water to cool them as quickly as possible. Reject any mussels that have not opened or are broken, then open each mussel;, discarding the empty half shell.
Arrange the mussels on a platter, cover with clingfilm and put into the fridge until ready to use.