Shellfish subdivide into two types:
- crustaceans such as lobster and shrimp that have an external skeleton;
- mollusks such as mussels and oysters that actually have an actual shell.
Snails that live in the water are often classified as Shellfish, too. But because most people ordering a fancy meal of Shellfish wouldn’t be impressed with a dish of snails, the popular, general definition of Shellfish doesn’t include them. Interestingly, octopus and squid are categorized scientifically as “cephalopods”, which makes them mollusks, which makes them Shellfish. But foodwise, you’re more likely to see them called just “seafood” rather than “Shellfish.”
The American Food and Drug Administration doesn’t include in its definition of Shellfish scallops that have been shucked so that just the adductor muscle remains.
If any Shellfish have a strong smell to them, don’t buy them. Their smell should be very mild.
Treat Shellfish as you would meat: do not put cooked Shellfish on a plate or in a container that has held raw Shellfish.
Do not overcook; one minute they are done, and the very next minute they will be tough.
Have a profound respect for just how perishable fresh Shellfish is. There have been too many unnecessary cases of food poisoning or upset tummies because of improper handling. Buy fresh Shellfish on the day you intend to use them — and keep them in the refrigerator until you do cook them. In the fridge, don’t have them in a sealed plastic bag, or they will suffocate. It’s just to put them in a bowl with a damp paper towel or cloth on top of them. Resist the temptation to put some ice cubes in the bowl: they do better at temperatures that are a bit warmer than freezing, ideally about 38 F / 3 C, and the ice cubes may melt, drowning your critters in fresh water, which they can’t live in.
Frozen will, in general, keep up to 6 months.
Store any cooked Shellfish in the fridge and use within three days.