Poaching is the technique of cooking foods over low heat in a gently simmering liquid. It is particularly appropriate for cooking fragile foods such as fish, lean poultry and meat, or fruit, that may fall apart, or dry out and toughen over a higher heat. It is also a good way to cook foods that are to be served cold. Depending on the food to be cooked, the liquid used may simply be water or a highly seasoned liquid known as a court bouillon, a flavoursome stock or wine, or a sweet syrup.
The temperature of the poaching liquid is all-important. It must be maintained at a bare simmer (the French say it must just frissonne, or shiver) - a more vigorous simmer may cause the food to fall apart or cook unevenly. A favourite method for poaching fish at Le Cordan Bleu is to bring the cool poaching liquid to a simmer with the fish, then remove the pan from the heat and let the fish continue cooking in the hot liquid; this technique ensures that the fish is gently cooked and is never overdone.
The choice of poaching liquid depends on the desired result. If you plan to serve the liquid as a broth or to make a rich sauce, a well-flavoured stock is indicated. For dishes that do not make use of the poaching liquid, it is appropriate to use a court bouillon, made by simmering water and wine and/or lemon juice with aromatic herbs and vegetables for 20 minutes. For poached fruits, a sugar syrup and sweetened, spiced wine are common poaching mediums; both may be reduced to make a sauce.
Poaching is ideal for cooking whole fish. Make sure that the poaching liquid is cold when you add the fish or the outside flesh will be overcooked before the inside is cooked through. It is helpful to wrap the fish in a tea towel before cooking to help hold its shape and make it easier to handle (poultry and large pieces of meat are usually trussed before poaching for the same reason). A fish kettle, a long narrow pan with a removable rack, is a perfect vessel for poaching a whole fish, but you may also use a large deep pan such as a roasting tin.