The best tips for searing tuna start with the fish itself: using a fresh, high quality cut will go a long way towards successfully searing tuna. After the fish is selected, there are numerous marinades or flavorings that can be added according to preference, and any will work as long as the fish is prepared properly for cooking. The searing should be carried out on a well oiled, very hot cooking surface for the best results.
Tuna are large fish that come in several different varieties. Ahi tuna and yellowfin tuna are popular choices for searing, but regardless of what type is selected it is of the utmost importance that it be very fresh and very good quality. Fish that has been frozen for shipment and then thawed for sale will not be as high-quality or have as pleasant a texture as fresh, never frozen tuna. Additionally, since searing tuna generally results in a very rare or even raw center, it is best to select steaks that were cut very recently from a freshly caught fish, and then kept adequately chilled.
The beast cut for searing tuna is a thick steak; definitely no thinner than 1 inch (2.54 cm), but preferably at least 1¼ inches (3.18 cm) thick. Thickness is important because, in order to get a nice brown crust on the outside of the tuna and still retain the rare center, the fish has to be able to cook on the edges without overcooking the middle. Some people might prefer to marinade before searing tuna, often with asian-inspired flavors such as soy sauce and ginger. A marinade is not necessary, however, and simple salt and pepper will still produce a tasty seared tuna.
Before searing tuna, it is important to bring the fish to room temperature so that it cooks evenly; searing chilled tuna might result in warm edges and an unpleasantly cold center. The tuna should be gently patted dry to remove any water from the surface that could interfere with the searing, and either the fish or the cooking surface should be generously oiled to prevent sticking. Whether the surface being used is a grill or indoor frying pan, it needs to be very hot for searing tuna: if the surface is not hot enough, the center of the steak will overcook before a brown crust can form on the outside.
Seared tuna is generally served somewhat rare in the center, often just barely warmed through or at room temperature. This can be accomplished by cooking the steaks over the high heat for a very short time, approximately 60 seconds per side or slightly longer for thicker steaks. If a raw center is not appealing, the steaks can be cooked longer to lessen the rareness.