Essences are good for using in cream and butter sauces, for mixing with lemon juice and oils for salad dressing, or reduced and added to butter to make a shellfish butter.
This recipe works for lobster, shrimp, or prawn shells (crab shells don’t give up much flavor or color and are usually too hard to process), and is one we developed at Stars in San Francisco in the early 1980s. I have since seen this method only in the restaurants of people who worked there, but it could be as old as the Hobart mixer. In the nineteenth century and early twentieth, the shells were processed in huge mortars with a pestle, but that practice disappeared along with slavery in the kitchen.
Classically, any essences made from shells (the classic sauce Nantua, for example) call for cooking the shells in the oven. Tossing raw shells in hot olive or canola oil in a frying pan for a few minutes until deep red is passable, but I hate the flavor the shells tend to get (with the inevitable overcooking) in the oven. Boiled or sautéed shells give a much subtler flavor.
If the shells are not cooked, steam them covered in
If using shrimp shells, grind the shells in a food processor just enough to break them up. If using lobster shells, just put them in the bowl of an electric mixer fitted with the dough hook or paddle, and turn on the mixer at the lowest speed possible for 15 minutes. Wrap some aluminum foil around the top of the bowl and the mixer arm to keep the lobster shells from jumping out of the bowl as they are being crushed. After 15 minutes, add
Add the remaining fish stock and mix on low speed until the shells are completely broken up in small pieces and the stock in the bowl has turned red, about another 15 minutes. The long mixing time is necessary to break up the shells gradually and extract the full flavor and color.
Scrape out all the shells and any essence sticking to the sides of the bowl into a sieve placed over a bowl.
Strain completely, pressing down on the shells, reserving the liquid and discarding the shells.
Refrigerate for up to 2 days or freeze for up to a month.
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