The grill offers you two ways of preparing tuna. One method is to grill a thinner tuna steak over high heat until it is cooked through. The other method is to quickly grill it over very high heat, searing the outside, which leaves the fish mostly raw, but seared tuna is an Asian favorite that's becoming more and more commonplace in the U.S.
The Basics of Grilling Tuna
No matter how you prepare tuna, always shop at a reputable market with only the highest quality seafood available. Look for tuna with deep red, even color without dark patches. Tuna is great for grilling and is uniquely meaty and delicious. Luckily, it is also easy to cook.
Tuna is a very lean fish and tends to dry out quickly on the grill. While serving with sauce will help, if you cook tuna beyond medium rare it is most likely be dry. To help combat dryness, you can marinate the tuna. Anything with a lot of acid will begin to cook the fish before it hits a heat source (similar to the way ceviche cures fish in acidic citrus juices), so the marinade should be pretty mild and the tuna should not marinate for very long. Use a drizzle of high-quality olive oil, herbs, spices, and a small amount of lemon juice or flavored vinegar and marinate for just a few minutes while the grill heats.
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Fully Cooked Grilled Tuna
If you choose a piece of tuna that is about 1-inch-thick, it will grill in about 8 to 10 minutes, provided that your grill is very hot. Remove tuna from the grill before the surface starts to get crusty and burns. Unlike beef, lamb, or pork, you do not need to let tuna rest before serving. Get it off the grill and onto the plate right away.
Seared Grilled Tuna
For seared tuna, purchase a piece of tuna that is about three inches thick. Prepare it simply with a light brushing of oil and a generous sprinkling of salt and pepper. Preheat the grill until it is very hot. The major difference between grilling and searing tuna is the level of heat. Some gas grills simply can not produce the intensity of heat necessary to properly sear a piece of tuna. In this case, use a heavy cast-iron skillet. The iron skillet will absorb and hold the heat, giving you a good sear as long as you preheat the pan. If you trust your grill to produce the level of heat needed, then go straight to the grate; otherwise, use the skillet or a heavy-duty griddle.
Charcoal grills will allow you to bank up hot coals under the grate to get the kind of intense heat you need. The tuna sears for less than one minute per side, leaving the interior raw. Sear your thick cut of tuna on all four or six sides for about 45 seconds per side. The result is a piece of tuna that has a fantastic seared crust all around and a heated but raw middle.
How to Serve Grilled Tuna
If you've cooked your tuna through and it's a little dry, or you just want to add more flavor, serve it with a sauce or a salsa. Pineapple ango salsa, ginger and lime sauce, or buttery lemon chive sauce all compliment grilled tuna nicely.
Thinly slice seared tuna the way you would a steak and serve it immediately with a spicy wasabi sauce or a balsamic reduction. Tuna can be served with grilled vegetables, rice, or as part of a Niçoise salad bowl.