Enzymes. Molting. Economics. And why soft-shell crabs cost more.
1-Minute NomNom
Why are the shells of soft-shelled crabs so soft? *poke* It might seem they are a different crab species, but they are not.
Crabs, like other crustaceans, have hard outer shells that do not grow as they grow. They discard the old shells (a process called molting), and grow new and bigger ones. Soft-shell crabs are simply crabs that have just molted but their new shells have not hardened yet.
When crabs are ready to molt, they release enzymes to dissolve the exo-skeleton (i.e. the outer shell), separating it from the hypodermis, which is a thin layer of cells under the shell. As it dissolves, the calcium carbonate, CaCO3, from the old shells are absorbed and stored. At the same time, the hypodermis produces a new, thin and soft shell underneath.
When this new shell is ready, the crabs molt. The crabs then use the stored CaCO3 to thicken the new exo-skeleton. The process takes a few days — the blue crab’s shell, for example, takes about 72 hours to harden fully — even though the hardening begins 3-4 hours after molting.
To get soft-shell crabs, experienced fishermen (crabbermen?) catch the crabs just before they molt. They then put them in tanks for monitoring. When molting is complete, the soft-shell crabs are sold. All this extra work and the short time window to do it is why, pound for pound, soft-shell crabs cost more than most other crabs on the menu.
If you have 4 minutes to spare, watch this video of the molting process – but in a water tank — for yourself (you can speed up the video by watching it at 2x the speed):
Second Helpings
If we would like to have fresh soft-shell crabs, we have to get the timing right. We have to look out for the seasons when they molt. In the US, the blue crab molts largely around the summer months, between May and October.
Feed Me!
Which places in the world have the best soft-shell crabs? Share them with me!
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photos: in order – depositphotos/asimojet; stevebonk; asimojet; nipitphand
