The next time you peel shrimp, don’t throw away the shells. With the shells from shrimp, crab, lobster, crayfish (or a mix), you can quickly and easily make a flavorful broth that’s a wonderful base for soups and sauces and for cooking dishes such as paella, gumbo, and risotto. You don’t even have to make the broth right away. Save the shells that you would have otherwise thrown away, wrap them in plastic wrap, and freeze them until you’re ready to make a batch of broth; they’ll keep for two months frozen, as will the finished broth.
Crush the shells and add aromatics for a bright, bold flavor
The most basic shellfish broth is made by simmering rinsed crustacean shells (and heads if you have them) in water. While this simple broth often suffices, adding aromatics, such as herbs and vegetables, gives the broth a fuller flavor.
Start by sweating the vegetables in butter or oil. A shellfish broth gains a fullness of flavor with an initial cooking of aromatic vegetables, a mirepoix, over low heat. Although you could skip this step and simply combine the aromatics with the shells and the water to make a decent stock, this method will more fully release the vegetables’ flavor into the liquid. I also find that a little butter or olive oil helps the broth tremendously; much of the flavor of crustacean shells is soluble in fat but not in water.
I usually use one medium carrot and one medium onion per pound of shells. (Keep in mind that shells have different weights, with shrimp being the lightest. It takes about 8 pounds of headless large shrimp to get 1 pound of shells, for example.)
Leeks are another aromatic option, as are shallots. Garlic, fennel, and celery are more potent in flavor, but depending on what you’re using the stock for, they can be delicious additions as well.
Crush the shells to draw out the most flavor. To get the most flavor, especially with the harder shells like lobster and crab, it’s important to crush them, breaking them into pieces. A food processor works well for most crustacean shells and heads. It quickly chops the shells into tiny pieces, extracting the most flavor. But beware: don’t put heavy crab shells or lobster claws in the processor or you’ll damage the blade. Crush these harder shells by hand, using a mallet, the end of a European-style rolling pin—the kind without the handles—or the backside of a cleaver. You might want to put the shells in a heavy plastic bag before smashing them to keep the pieces from flying around the kitchen.
Although uncooked shells give the strongest flavor, you can make a good broth from lobster and crab shells that have already been cooked. You may want to freeze shells left over from a lobster dinner. When you add the shells to the pot, sauté them for a few minutes to release their flavor into the fat.
Add water to cover the shells. Once you’ve sautéed the shells and aromatics, add the water. For a pound of shells, add about 4 cups water, which makes an intensely flavored broth. A higher ratio of water to shells isn’t a cardinal sin, however. (If you’re scant on shells, you can also add a little chicken or fish broth to boost the flavor.)
Other flavorful additions include tomatoes, herbs, and spices. I add a tomato, coarsely chopped, with the water for a little acidity and to enhance the color of the broth.
While the broth simmers, you can add other flavorings. I usually add a bouquet garni—a small bunch of parsley, a bay leaf, and some thyme sprigs tied together—but there are many other options. Tarragon, either included in the bouquet garni or chopped and added at the end, is a favorite of mine. A pinch of Spanish saffron is the classic addition for a seafood paella, while steeping scallions and slices of ginger in the broth would make sense for an Asian dish.
Simmer the broth for half an hour, or as long as 45 minutes, but longer cooking won’t improve the flavor and may even hurt it. Skim off any scum that comes to the surface.
Use care when straining lobster or crab shells. Sharp, heavy pieces of lobster or crab shells can tear a fine-mesh sieve, so start by straining the broth through a sturdy colander. Push down hard on the shells to extract their juices. Then use your finest mesh sieve to sift out pieces of disintegrated shell.
Taste after straining. This broth isn’t meant to be eaten on its own, but it should have a pleasantly sea-like flavor. Don’t add salt until you’re ready to use the broth, especially if you’re reducing it as the base for a sauce; depending on your recipe, you’ll want the broth more or less salty.