Tuna, a naturally meaty, oily fish, is most often available as large steaks. Cut to 1 or 1 1/2 inch thick, tuna steaks are flaky, firm and rich tasting when cooked. Boiling fresh tuna steaks helps preserve the fish’s natural moisture, as overcooking in high heat conditions can lead to dried out, chalky textured fish. Marinate your tuna steaks before cooking and flavor the boiling liquid to gently season your steaks.
Choosing the Steaks
Tuna steaks, regardless of the type of tuna need a firm texture and no signs of browning or discoloration when raw. Good quality tuna steaks will have a meaty aroma and meat that is either dark or deep red. Steaks can be bone in or boneless, but because tuna is a large fish, the steaks are most often sold deboned and almost always sold skinned, as the tough skin is inedible.
Flavor the Steaks
Do not wash your steaks before cooking, pat them dry with paper towel. Tuna steaks can be cooked as is, but marinating gives the meat a chance to pick up more flavors. Rub dried spices, such as oregano, thyme and rosemary, directly onto the flesh and let sit, in the fridge in a food-safe container, for a minimum of 20 minutes. Fresh herbs and spices can also be used, as can oil or acid based marinades. Mix soy sauce, sesame seed oil, minced ginger and garlic and toss your steaks in the marinade to evenly coat, letting rest for at least 10 minutes before cooking. Wet marinades penetrate the flesh more quickly than dry rubs.
Flavor the Cooking Liquid
You can always add flavor to your boiled tuna by seasoning the cooking liquid instead. Use the same seasonings for your cooking liquid as you would for marinating — so in the case of a dry rub, add the dried spices directly to the cooking liquid. Bring the liquid to a rolling boil, 212 degrees Fahrenheit, before cooking the tuna. You can also boil your tuna in liquids other than water, such as stock or diluted white wine. Cooking your tuna in flavored liquid will lead to a more gently seasoned steak, as there is less time for the flavors to penetrate the flesh.
Doneness and Tuna Fish
A 1 1/2 inch thick tuna steak, weighing around half a pound will cook in roughly 10 to 15 minutes at a rolling boil. Cover the pot when boiling the steaks for faster cooking. Tuna needs to be cooked until the internal temperature reads 145 F for guaranteed food safety as set out by the U.S. Department of Agriculture. However, overcooking tuna, even during boiling, will lead to dense, hard meat and a chalky texture. Because of this, tuna steaks that have been frozen and defrosted correctly in the refrigerator, are best cooked only to medium rare, or an internal temperature of 125 F. This helps you avoid ruining your steak.
References and Resourcesthe kitchn: Build a Menu -- 5 Tips for Matching Side Dishes with Main Dishes
The World's Healthiest Foods: Tuna
FoodSafety.gov: Safe Minimum Cooking Temperatures
Joy of Cooking; Irma S. Romabauer