Tuna is a naturally fatty fish, with a rich taste and firm flesh. Most commonly sold as steaks, steamed tuna takes advantage of the fish's natural richness. Because steaming let's tuna's naturally strong taste shine through, it means the steaks can be successfully paired with stronger flavors, such as ginger or garlic. Tuna steaks are always sold skinless, due to its thick, coarse texture.
Choosing Tuna Steaks
Tuna steaks come with the bone-in or boneless. Bone-in steaks take a little longer to cook, but some people believe the bones add extra flavor to the cooked fish. While there are many types of tuna, look for trimmed steaks with firm meat. They should have a clean, meaty -- not fishy -- aroma. Tuna should be dense or dark red, and have no discoloration, including near the bone. Choose tuna that is sustainably harvested, as some tuna, such as bluefin tuna, are over-fished nearly to the point of extinction.
Remove any excess streaks of white -- cartilage and skin -- that may be on the steaks, using the point of a sharp knife. Pat dry the tuna and sprinkle sea salt, pepper and any other seasonings you may want to use. Seasoning your tuna with acid, such as lemon or lime juice, adds flavor, but letting it sit "cooks" the fish. It's best to season with lemon or lime after cooking. Fresh herbs and aromatics, such as minced ginger, cilantro and green onion, can be rubbed directly onto the steaks. Let the tuna sit for 10 minutes to 2 hours to give the seasonings time to penetrate.
Steaming the Steaks
Place the steaks in a shallow heat-proof bowl with a rim. The rim lets you trap the juices during cooking. You can also place your steaks over a layer of fresh herbs or vegetables -- such as ginger and green onion or shredded Nappa cabbage -- in a shallow bowl or steamer. A steamer allows more steam to reach the fish, while a bowl lets you capture the liquid exuded by the fish during cooking. Heat your water until it reaches a rolling boil -- 212 degrees Fahrenheit -- and carefully lower a steaming rack into the pot. Season the water with dried herbs or wine to gently season your fish during cooking. Place the bowl or steamer with the fish into the pot and cover. Cook a 1/2 pound steak, roughly 1-inch thick for 10 minutes, adding an extra 2 minutes of cooking time per 1/2 pound.
Doneness and Serving Ideas
Tuna is best when cooked to medium-rare, as overcooked tuna becomes dry, hard and has a chalky texture. Overcooked tuna also loses its naturally rich flavor. Cook until the internal temperature measures 125 F with a food thermometer. A food thermometer is the only way of guaranteeing the correct degree of doneness, as visible signs -- the flesh will firm up and turn opaque and white -- may mean the inside is undercooked. Serve your steamed tuna over rice or cooled to room temperature with leafy greens for a healthy salad. Dress the fish with the juices collected during cooking, or use some of the steaming liquid mixed with olive oil, white wine vinegar and minced garlic for a fast, simple dressing.