Small, oily and forgiving in a way that lean white fish isn't — the fat protects it, so the window is wider and the skin crisps easily. Farmed rainbow trout is also one of the few fish that is both cheap and a genuinely sound environmental choice.
Trout are salmonids, related closely enough to salmon that steelhead — a sea-run rainbow trout — is often sold and cooked as salmon and looks nearly identical. Most sold is farmed rainbow, at ten to fourteen inches and under a pound, generally sold whole or butterflied. Butterflied trout is split along the belly with the backbone and rib bones removed, leaving the two fillets joined at the back with the skin on — which is the most useful format, because it cooks in four minutes and there are no bones to negotiate. The pin bones along the centreline of a fillet run at an angle and need tweezers. The skin is thin and crisps unusually well.
Trout carries 5-8% fat depending on species and diet, well above halibut or cod, and that fat is doing the same protective work that intramuscular fat does in beef — it renders slightly, coats the fibers and keeps the fish tasting moist several degrees past where a lean fish would be dry. The practical result is a window of maybe ten degrees rather than five. The flesh sets at around 120-125°F and holds up well to 135°F. Colour varies from white to pink to orange depending on diet, since the pigment is astaxanthin from crustaceans or feed, and says nothing about quality or species. The thin skin has less collagen than a salmon's and crisps faster, in two to three minutes.
The fastest good dinner in the fish case — four minutes total, and the skin crisps into the best part.
HowDry the skin thoroughly, salt it, and lay it skin-down in a hot pan with a little oil, pressing flat for the first twenty seconds so it doesn't curl. Three minutes on the skin, then thirty to sixty seconds flesh-side. Butter, lemon and capers off the heat.
The bone and skin protect the flesh and add flavour, and a whole small fish is very hard to overcook.
HowStuff the cavity with lemon, herbs and butter, score the skin, and roast at 425°F for twelve to eighteen minutes, or grill over medium for five to six minutes a side in a fish basket.
The fat content makes trout ideal for smoking — lean fish goes dry and papery, oily fish absorbs smoke and stays succulent.
HowBrine in a 5% solution for two hours, dry uncovered in the fridge until a tacky pellicle forms, then hot-smoke at 180°F for one and a half to two hours to 140°F internal.
The classic treatment for a small delicate fish: flour, butter, lemon, and nothing that competes with it.
HowDredge lightly in seasoned flour, fry in foaming butter three minutes a side, then finish the pan with more butter, lemon juice and parsley and pour it over.
Trout skin is the best thing about the fish and is easily wasted. It's thin, and it needs a genuinely hot pan and a properly dry surface to crisp — into a lukewarm pan it sticks and tears, and with any moisture on it, it steams into something grey and flabby rather than crisping. Pat it dry, salt it fifteen minutes ahead and pat again, and press the fillet flat for the first twenty seconds so it doesn't curl away from the heat. The bone problem is separate and more annoying: whole trout have a row of fine pin bones running along the centreline of each fillet at an angle, and butterflying removes the backbone and ribs but not those. Run a finger along the line to find them and pull each with tweezers in the direction it points, or accept that everyone at the table will be picking them out.
Farmed rainbow trout is one of the better environmental choices in the case — raised in freshwater raceways with low impact and a good feed conversion ratio — and it's cheap. Buy butterflied if you can; it's the most useful format and most counters will do it. Whole fish should have clear rather than sunken eyes, bright red gills, firm flesh that springs back, and no smell beyond clean water. Steelhead is sold as trout or as salmon depending on the shop and is excellent either way. Flesh colour ranges from white to deep orange depending on feed and tells you nothing about quality. One butterflied trout or one whole fish per person.
Doneness: 125-135°F, which is a wider window than lean fish thanks to the fat. Whole fish is done when the flesh at the thickest point near the spine has just turned opaque and pulls from the bone. Hot-smoked to 140°F.
Steelhead is a rainbow trout that migrated to sea and it looks and cooks almost exactly like salmon, so the two are frequently substituted. Freshwater rainbow trout is smaller, milder, less fatty and more delicate, and it's better suited to fast pan cooking than to the thick-fillet treatments salmon gets. In a recipe, small trout and a salmon fillet are not interchangeable on timing — the trout will be done in a third of the time.
Diet. The pink and orange colour in salmonids comes from astaxanthin, a carotenoid the fish get from crustaceans in the wild or from feed in farms. A trout raised on a diet without it is white-fleshed, and it tastes the same. Colour is not a quality signal in either direction, and in farmed fish it's essentially a formulation choice.
It's the best part if you cook it properly. Trout skin is thin and crisps in two or three minutes into something close to a crisp, which is why the skin-down pan method is worth the effort of drying it. Skin that's been steamed or poached is unpleasant and worth removing. If you're not going to crisp it, take it off.