Prawns can be purchased raw or cooked, with heads on or off. It is most economical to buy tails only, as more meat is obtained by weight. However, a whole prawn has more flavour, as do the heads and shells of any shellfish. Even if you are buying them pre-cooked, they will be full of flavour and can be used to produce excellent stocks and sauces. Prawns are generally graded by size for sale and are sold by weight, so the bigger they are the more expensive they will be. As an approximate guide, 20–25 prawns per kg yields prawns of a suitable size for most recipes. Unless local and fresh, prawns are either cooked as soon as they are caught or are deep frozen because, as in the case of crab and lobster, the meat loses flavour and texture very quickly. So even when a sign in a fishmonger says ‘fresh prawns’, unless locally caught, they may be frozen and defrosted. Where possible buy prawns still frozen, rather than defrosted, as they deteriorate quickly after defrosting. When checking for freshness, look for tails that are still firm and taut. There should be no obvious discolouration.
1. Hold the prawn by the tail. Using your other hand, twist the head and pull it away from the tail. Put the heads aside (they can be frozen along with the tail shells and used later to make shellfish stock).
2. The tail shells are soft and hinged and can be removed piece by piece or in several pieces at a time. Start to peel away the shells from the underbelly of the prawn. The tail tip can be kept on or carefully removed.
3. Make a shallow incision, 1–2mm deep, down the length of the back of the tail to expose the intestinal tract. (This is usually dark, but it can be almost translucent.) Carefully pull this away and discard. The prawn tails are now ready to cook.