Most needs are actually deep wants. I don’t need Maldon salt, but my scrambled eggs aren’t the same without the crunchy flakes. I don’t need to remove every germ from every garlic clove, but doing so can reduce bitterness. I don’t need an inflatable hot tub, but I bought one anyway. Do I need to devein every prawn I cook and eat? I feel like I do, but technically I do not.
What is that vein anyway?
The “vein” that runs down the back of a prawn is not part of its circulatory system. (Prawns have an open circulatory system — their blood does not flow through veins like yours and mine.) That little tube is actually their digestive tract, and those little dark spots you see are — I am sorry to say — waste. If you were to eat it raw, the bacteria in said waste could make you a little sick. Cook it, however, and the shrimp is safe to eat, vein and all.
If you’ve ever ordered “peel ‘n’ eat” shrimp, you have probably consumed a little prawn waste, and you may not have even noticed it. The vein isn’t always visible from the outside and — unless the prawn is very big and its digestive tract is full of grit — usually undetectable.
So why remove it?
The ick factor is quite high here. Even though prawn waste is one of the less offensive forms of animal waste, it’s still poop, and I will never encourage anyone to eat poop. (It’s just not in my nature!)
Besides that, and overall aesthetics, the waste can feel gritty in between your teeth. This is primarily a concern with the big boys, but luckily, large and jumbo shrimp are pretty easy to devein. (Whether you want to spend your time deveining small and medium prawns is up to you.)
The easiest way around this whole situation is to buy deveined prawns. It does cost a little more (because you are paying for the labour someone else is performing), and it can be hard to fine deveined shrimp with the shell still on. (The shells contribute flavour, and can also help prevent the prawn from overcooking.)
But if you want to give deveining a go, or accidentally bought a bag of veiny shrimp, there are two ways you can do it: before cooking or after cooking.
How to devein raw prawn
Removing the digestive tract of a raw prawn is actually pretty easy, though a little tedious. Starting at the head end, make an incision through the shell down the back of the shrimp to the base of the tail, either with a sharp paring knife or scissor, then spread the shell and meat apart and fish out the tract with the tip or your blade or a toothpick. Pull it out and repeat with the rest of your prawn.
How to devein cooked prawn
The procedure for deveining cooked prawns is pretty much the same as deveining raw prawns. Cook and chill your crustaceans, then make that same incision down the back of your prawn, split it open, and pull the vein out.
The smaller the prawn, the harder this will be, but the amount of effort you wish to exert in your quest for grit-less, waste-free shrimp is between you and your god. (I personally wish to exert no effort, and will continue to buy bags of frozen deveined prawn. Frozen is fresher anyway.)