First things first: If you've been buying precooked shrimp, or even pre-peeled and pre-deveined shrimp, stop right this instant! I mean it!
Precooked shrimp are unfailingly pre-overcooked-shrimp, and it's impossible to add flavor to them the way you can with raw shrimp. Shrimp that are raw but peeled and deveined are a small step up, but they often get mangled and beaten up in the cleaning. You are much better off buying whole, headless shrimp (or, at the very least, easy-peel) and cleaning them yourself. It's a little more work, but worth the effort. The video above will show you everything you need to know.
Shopping and Storage
There are a number of choices to make when you're buying shrimp:
- Frozen versus fresh: The vast majority of shrimp are processed and frozen right at the farm or on the boat before they ever get anywhere near your fishmonger or supermarket. This means that the "fresh" shrimp you're seeing at the fish counter are simply frozen shrimp that have been defrosted and put on display. There's no way to know how long they've been there, so you're better off buying frozen shrimp and defrosting them at home. In a bowl under cold running water, shrimp should take about 10 minutes to defrost. Small price to pay for freshness.*
- IQF versus block frozen: IQF stands for "individually quick frozen," and means that each shrimp was frozen on its own before being bagged. Block shrimp come frozen together in a large block of ice. As a general rule, the faster you freeze something, the smaller the loss in textural quality, so go with the IQF. They also have the advantage of being much quicker to defrost.
- Size: Forget labels like "medium," "large," or "jumbo." These are unregulated terms that are decided on by the packager or the supermarket. Instead, look for a set of two numbers, such as 26-30 or 16-20. These indicate the number of individual shrimp that it takes to make up a pound. So a package labeled 16-20 will contain shrimp that weigh in at a little less than an ounce apiece. The smaller the number, the larger the shrimp. For super-large shrimp, you may see a number like U-15, which means that it takes under 15 pieces to make up a pound. There's not much difference in flavor between the sizes—look to individual recipes to specify the right size of shrimp you need.
- Additional ingredients: Shrimp, like scallops, are often treated with STP (sodium tripolyphosphate), a chemical designed to help them retain moisture. More than anything, this is a ploy to bulk up their weight and sell them at a higher price. Check the ingredient list on your package of frozen shrimp. It should list shrimp, possibly salt, and nothing else.
* NB: Some really good fish markets will offer never-frozen wild shrimp. If they carry these, they will advertise them as such. As long as you can trust that they are fresh, snatch 'em up and eat them immediately! They're a real treat.