There are crabs in all the world’s oceans, in freshwaters and on the
land. I once met a man in Rarotonga called Piri Puruto (‘the Coconut
King’) who kept large red land crabs as pets – crawling free around the
living room. The smallest is the minuscule Pea Crab which lives inside
oysters, and the largest is the Japanese Spider Crab, with a leg span
of up to 4m.
You don’t want to be an Alaskan King Crab fisherman; 300 of every
100,000 are killed every year, the highest fatality rate of all
Like all crustaceans, crabs moult. When their ‘shell’ becomes too tight for comfort, they grow a new one underneath, lose enough muscle to be able to squeeze out of the old one, take on huge amounts of water to stretch the new, still flexible ‘cuticle’ as far as it will go, then gradually replace the water with new tissue. So it’s best to avoid buying or eating a crab which is just about to moult (too shrunken) or which has just moulted (too watery).
Like lobsters, crabs tend to be sold alive or cooked, rather than just dead, as once dead their livers produce an enzyme which rapidly attacks and breaks down the organs and flesh, rendering them mushy and stinky.
If faced with a live crab to cook, here’s how: You can keep him/her in a moist wrapping in the fridge for a day or two if you need time to contemplate your intentions. When it’s time to say your goodbyes, put it in the freezer for a couple of hours to numb its senses. Don’t worry, this won’t freeze it, they’re used to cold climes. Make plenty of strong brine – dissolve 100g (3½ oz) salt in every litre of water, which should be salty enough for a raw egg to float at the surface – and bring it to a rapid boil. Weigh the by now unconscious crab and then plonk it in the water without a second thought and clamp a lid on. (You can do this without chilling the crab first; in this case be prepared to hold the lid down very firmly.) Bring the water back to a boil, reduce the heat and simmer for 15 mins for the first 500g (1 lb 2 oz) plus an extra 10 mins for every extra 500g. Once you’ve dismembered the crab and picked out all the meat – a tedious job requiring lots of white wine and a friend to help – keep it chilled til needed.
Also in common with their fellow crustaceans, crabs go through a remarkable colour-change when cooked. This is because their dark blue-green-red-brown colour is formed by carotenoids (from the plankton in their diet) bound with protein molecules, which are denatured during cooking, leaving the carotenoids free to show their true carroty colours.
Crabmeat tends to taste great because it is full of tasty amino acids, which give it its rich, sweet and savoury flavour. All shellfish share this feature, due to the fact they must increase the ‘saltiness’ of their bodies to balance that of the sea, presumably so that they don’t dehydrate through osmosis.
‘Crab’ derives from the Indo-European word ‘gerbh’, which means to scratch or carve. Piri Puruto’s pet crabs certainly had this ability. ‘Crustacean’ shares an Indo-European root with ‘crystal’, as both involve substances ‘frozen’ into ‘crusts’, of sorts. (Which is more fascinating – food itself or the words we use for it?)
On Food and Cooking, Harold McGee, 2004
Fish, Sophie Grigson and William Black, 1998