Mussel soup is any soup base that has been flavored with and contains the underwater animal known as a mussel. These small creatures may be purchased from local seafood markets, or plucked fresh clinging to the sides of wave battered rocks. They are often cooked using a steaming method prior to placing in soup, and may be accompanied by other shellfish such as shrimp, oysters, and clams. This type of soup is typically prepared using a thick base of cream, though some few recipes use a liquid broth instead.
A mussel is a small, underwater creature often referred to as a mollusk. It lives in a hard, hinged shell that is symmetrical and typically oval in shape. It may be found in fresh or salt water, and the shape and coloring of the exterior shell is typically determined by the type of mollusk and its native habitat. Shells may appear shiny when underwater and range in color from black to blue, brown, yellow, and green. Mussels feed on microscopic creatures which they suck into their digestive systems through their shells, and naturally filter any water which they expel.
Only live mussels should be used in mussel soup. These small mollusks may be found clinging to the sides of wave crashed rocks and hand picked by adventurous chefs for use in recipes. Those less inclined to brave inclement water conditions may purchase them from local seafood markets. These animals taste best when used soon after purchase, and should typically not be frozen prior to cooking. If the shell of the mollusk is already open prior to being cooked, the animal inside may already be dead and should be thrown away. An open shell may also be a sign the animal is merely resting, and to test whether it is alive, cooks can rap the shell gently against the countertop to see if the creature will snap its shell shut in response.
Live mussels can be steamed before being placed in the mussel soup, which aids in removing them from their shells. A common method of steaming involves sauteing the shells in garlic in a sauce pan before covering them slightly with white wine. This mixture can be allowed to simmer for several minutes until the shells open naturally. Any unopened shells tend to indicate the creature inside was already dead before being placed in the wine, and should be discarded. If the majority of shells simmering are unopened, they have likely not had adequate time to steam and can continue cooking for several minutes more.
The base for the mussel soup can be prepared using any reserved wine from the steaming mixture. This wine should be strained first to remove any sediment that may have detached from the shells while being cooked. A wide variety of herbs and thickeners may be added to the wine, depending on the preferences of the chef. Common choices include fish broth, chicken broth, shallots, parsley, and heavy whipping cream. Once the base has been cooked through, the mussels can be scraped from their shells and added back to the soup a few minutes prior to serving.