Prawns and shrimps belong to the same family as crabs and lobsters and are similar in a number of ways. They are decapod crustaceans, which means that they have 10 legs and a hard shell covering their body, although the shell that covers prawns and shrimps is much thinner and not as hard as the shell of most other crustaceans.
As with crabs and lobsters, shrimps and prawns must shed their shells in order to grow bigger. There over 300 different species of prawns and shrimps, which are found in most waters all over the world. They are fished in both the ocean and fresh water, and are farmed as well as wild.
When cooked, the shells turn pink and the sweet, meaty flesh turns white tinged with pink; brief cooking is essential, otherwise the flesh will become tough. As with other types of crustacea, prawns fished in cold waters tend to be more flavourful than those from warm waters. Although anatomically incorrect, the part of the prawn eaten, the meaty body, is referred to as the tail. The very small shellfish referred to as shrimps are prawns, too – the term shrimp just indicates their diminutive size.
Generally fresh, uncooked prawns will be anything from translucent to a bluish grey. However, stay away from prawns that are discoloured in the head or shell, or inconsistent with the rest of the prawn, as this can suggest the flesh is starting to go off. In this case, the prawn will often also feel slimy and smell strongly of ammonia. Fresh prawns should smell salty, feel firm and have a nice shiny outer.
If you are buying shell-on prawns, buy double the weight that you would need of shell-off prawns.Tiger or king prawns, which are big and juicy, are the types most commonly sold raw, either whole in their shells, or with their heads removed
The best way to store them is on ice until they are required for cooking. Be aware that freezing in fact does not significantly alter the flavour profile of the prawn, so if you are not able to buy prawns fresh from the markets like this, buying them frozen is also fine – as long as they are not pre cooked.
If the prawns are shell-on, you’ll need to peel them. This can be done before or after cooking, but peeling them after cooking makes for a juicier, more flavourful prawn.
Grip the body of the prawn in one hand and twist the head off with the other (this can be used to make stock). Turn the prawn over and pull the shell open along the length of the belly, working from the head end downwards
Once the shell is off, check to see if there is a black line running down the back of the prawn. This is the intestinal tract – if it’s black, it’s full. It’s not harmful to eat, but the prawn looks better without it, and it can be a bit gritty. Removing it is called ‘deveining’. Using a small, sharp knife, make a shallow cut along the length of the black line, then lift it out using the tip of the knife.
To butterfly a prawn, peel and devein as above, leaving the tail on. Then make a deep cut along the belly of the prawn, open it out and press it down so that it’s flat. If you want the prawns to be straight, peel (leaving the very end of the tail on) and devein, then insert a wooden skewer along its length.