In both cases beneath, I steam the PEI mussels for 5 mins. on low heat, on a pan on my stove in 100 mL of white wine. I live in Toronto, Canada.
Case 1: Live mussels from Pusateri's or Whole Foods Market.
They're individually picked as in the left picture beneath, in a string bag like on the right.
or vacuum-packed. Most meat shrink and wither after the 5 mins. of cooking. The meat aren't clumps as they ought be, and can't be plucked. Rather, the meat has crumbled and dismantled, and I have to scoop the spindly slivers of meat with my spoon. See beneath.
Case 2: I've bought PC's Cooked then Frozen PEI Mussels weekly for the past year.
By comparison, every time that I steam these, the edible meat is fleshy like the picture on the right.