It's 1998. Google is a newborn company that no one yet suspects will influence nearly every aspect of our lives. The world waits with bated breath after Ross accidentally says Rachel's name at the alter. And fancy restaurants all over the United States are serving plate after plate after plate after plate of grilled tuna.
That we've never had an in-depth grilled tuna recipe on this site, since its founding more than 10 years ago, is not an accident. It's dated. Add to that serious concerns around overfishing of tuna, and there's good reason to avoid it. And yet a pristine slab of tuna, seared over high heat with a perfectly rare center is a lovely thing. In my opinion, it's okay to make it on occasion, as long as you buy your tuna responsibly.*
*This is a concern with most edible creatures from the sea, but many species of tuna are in an especially precarious situation.
If you do decide to make grilled tuna, you want to make sure you do it right. Tuna ain't cheap—especially not the quality you'd want to eat near-raw after a quick jaunt on the grill—so ruining with bad technique is as close to unacceptable as it gets. Let's make sure that doesn't happen.
How to Choose Tuna Steaks for Grilling
Buying tuna should start with researching sustainability. There are many species and sources of tuna that we should all do our best to never buy, whether from a fish market or at a sushi restaurant. There are far too many details to list here, so make sure to head over to Monterey Bay Aquarium's Seafood Watch resource to see which types of tuna from which regions, and caught using which harvesting methods, are the most sustainable. I can't remember, for example, the last time I ordered bluefin tuna sushi and neither should you—no matter how loudly that meltingly fatty toro calls to you. I rarely make pronouncements like this, but some types of tuna are under such extreme threat that an equally extreme statement in support of protecting them shouldn't be controversial.
Assuming you've tracked down a source for tuna that doesn't violate the "never buy" list, you'll next want to think about freshness. You want a piece of fish that's sushi- or sashimi-grade...except that those terms don't really mean anything. They're marketing language, meant to signal that the fishmonger feels confident that the fish you're buying is safe to eat raw. Whether you trust your fishmonger is an entirely different question.
Then again, tuna is one of the very few fish that generally must be processed such that parasites have been killed by extremely cold freezing temperatures. In this respect, at least, tuna is a safer bet than many other fish we commonly eat raw or minimally cooked.
Now, assuming you've found a sustainably caught and safe-to-eat-when-raw piece of tuna, the next thing you'll want to think about is the size and dimensions of the tuna steaks themselves. Tuna is best when it's still more or less raw in the center, since most of the flesh, save the belly, is exceedingly lean and prone to grotesque levels of dryness when cooked even halfway to well-done (one of the reasons we also like to cook tuna sous vide). That means you want a thick piece of fish.
Ideally your tuna steaks should be at least an inch-and-a-quarter to two inches in thickness, which will allow you to sear each side while still leaving enough meaty matter in the middle to remain mostly untouched by heat. Much like a few extra pounds of flab will help distance your internal organs from winter's biting cold, an extra eighth-of-an-inch or more on each side of your tuna steak will leave you with a solid one inch of more or less sushi-like rawness in the center, which is what you want. (If that's not what you want, you're better off doing an entirely different tuna preparation instead, like slowly poaching it in olive oil; or just buy a can.)
How to Grill Tuna Steaks: Step by Step
Step 1: Prep Your Grill
Setting up your grill for tuna steaks follows the same basic best practices for grilling anything else. You want to preheat your grill and grill grate, clean the grate well with a grill brush, and finally oil the grate. A hot, clean, and oiled grill grate will be much less likely to severely stick to your fish than a gunky, cold one.
Because you want to sear your tuna steaks as quickly as possible to minimize the amount of heat penetration, you'll be cooking over the hottest coals possible. You can set your grill up as a one- or two-zone fire, depending on what else you're cooking. There's little chance you'll need a cooler area on the grill to finish your tuna: as soon as it's seared on both sides, it's done.
Step 2: Prep the Tuna Steaks
While your grill is preheating, you can prep your fish. It's important to dry the fish well on both sides, using paper towels—minimizing surface moisture helps speed the searing process along and reduces the chances of the tuna sticking to the grill.
To that end, I also like to lightly rub the dried steaks with a neutral oil like canola or vegetable oil. It's just one more bit of insurance against sticking.
Step 3: Grill the Tuna
Salt draws moisture out of proteins like fish and other meats, so I make sure to sprinkle it on the tuna at the last second. After we've made sure to dry the surface of the fish well, the last thing we want to do is get it wet again before putting it on the grill.
Set the tuna steaks over the coals. Your goal here is to get a sear on the exterior as quickly as possibly, while minimizing how much heat penetrates to the center. Even with all of the preparations we've made, the fish will still likely stick to the grill grate at first, so do your best to refrain from attempting to lift or move the steaks prematurely. They should release on their own once they've browned well.
If the fish has adhered to the grill grate at all, the best way to release it isn't to try to force a metal spatula underneath. Instead, slide a thin metal tool, like the tines of a carving fork, large culinary tweezers, or even the spatula blade itself, down between the grill grates and under the fish. Then gently lift from below, being careful not to force it if it's stuck on tight.
Because of how rare I think grilled fresh tuna should be served, I don't bother with thermometers. There's nothing to measure: Just sear both sides and then pull it off the grill right away.
Still, I understand that people want a little more guidance than just that. What I recommend is to watch the edges of the tuna steak. Tuna is remarkable among fish in that its color change from raw to cooked is so dramatic. Raw tuna is a deep, dark purple-red hue, but once heat touches it, it comes a light beige. By observing the sides of the steak you can get a sense of just how far the heat is reaching into it. Just keep in mind that because heat will swirl up and around each steak, the exterior edge will still cook more quickly than the interior, so it'll begin to shift towards beige before the inside does.
When it's done, remove it from the grill and slice it with the sharpest knife you have, ideally a thin-bladed one like a slicing knife. I think it's good simply drizzled with fresh olive oil and a sprinkling of salt and fresh black pepper.
No matter how you serve it, remember that there's no rush. Because the tuna is so rare in the center, it's not really something that starts out all that hot in the first place—it's just as good at room temperature, or even cold. If you want proof, look no further than the millions of fresh-tuna Niçoise salads that once dominated restaurant menus. Though I'd suggest making a Niçoise with canned tuna instead. One of the worst things about that '90s trend was that rare tuna ended up in everything, even when it wasn't helping the dish.