Larger shrimp, sometimes called prawns, usually have a long black line running across the back of the shrimp from top to bottom, and located right underneath the shell. This is actually the shrimp’s intestinal tract, and it may contain undigested particles of food or grit, so many people prefer to remove this strip. This process can be made easier by using a devein knife.
The devein knife, sometimes called a devein tool, is a small sharp knife with a narrow tip. In fact the widest part of the knife is right at the handle. The blade then gets progressively narrower until it merely forms a small sharp tip. In order to properly remove the vein from the shrimp, you’ll need to depend upon a sharp knife, since most recipes recommend deveining prawns prior to cooking.
You do have to be a little bit careful when you work with shrimp. Most of them are little bigger than palm size, and you need to be precise in your cuts. To devein the shrimp, you hold it in your hand, with the back facing up, and use the devein knife to make a small incision along the whole back of the shrimp. You should hold the shrimp as high up in your fingers as you can so that your fingers remain away from the devein knife.
The sharp devein knife should easily slit the back of the shrimp shell. From there, you can usually merely pull out the vein with fingertips or toothpicks. You can use the devein knife to loosen the vein at one end so it can be stripped off the shrimp.
If you prepare shrimp often, you’ll probably want to keep one of these knives on hand, or perhaps a couple of them so a few people can devein shrimp at the same time. Prices vary, but since you do want a very sharp knife, expect to pay about $30 US dollars (USD) for a good quality one. On the other hand, if you seldom prepare shrimp, you can also devein with a simple paring knife. This can be a money-saving move, since you’ll get much more use out a paring knife on a regular basis than you will out of a devein knife.
For very small shrimp, you may not need a deveining knife. Often these are sold shelled and with veins removed. Further, deciding to remove the back vein of a shrimp is a matter of preference. They don’t really appear to affect taste much. If you’re not picky, there’s no need to remove the vein.