Tuna's succulent flesh absorbs marinade quickly, making it a poor candidate for overnight preparation. For tuna tartare, called ahi poke in Hawaiian cuisine, you want the texture of raw fish. When it soaks too long in marinade, especially one containing citrus juice or vinegar, the appealing pink flesh turns gray. It can also lose its creamy mouthfeel, developing the consistency of commercially canned tuna – fine for a tuna salad sandwich but not a tartare.
Tuna tartare is typically composed of finely diced fresh tuna and minced herbs and seasonings ranging from citrus juice or vinegar to garlic or shallots, sesame, ginger, soy sauce, scallions and chili peppers, all held together with oil. It might be presented with avocado, crackers or a lightly poached egg on top. Serve it immediately, or marinate the tuna in the refrigerator for up to 15 minutes.
Any raw food preparation carries a greater risk of foodborne illness than does a cooked dish. To minimize this, purchase scrupulously fresh fish. Sushi- or sashimi-grade tuna costs more, but it typically gets flash frozen, which kills potentially harmful microbes, explains food science expert Harold McGee in “Keys to Good Cooking.” Hold the fish until serving time in the refrigerator, and clean your hands, all utensils and your work surface with soap and hot water both before and after you prepare the dish.