Cut the bloodline out of tuna.

Do it. It’s the dark, red-brown strip running along the center or side of the steak, and it’s where the strongest, fishiest, almost metallic flavor lives. Remove it if you want clean-tasting tuna.

The bloodline isn’t actually blood — it’s a dense, fatty muscle that stores more myoglobin and enzymes. That’s what gives it that sharp, gamy taste. Cutting it out is straightforward: lay the steak flat, slide a sharp knife under the dark part, and slice it off in one piece. Don’t worry about wasting meat — you’re removing maybe 10-15% of the steak, and the rest will taste miles better.

Some people simmer the bloodline in soy sauce or broth for soup or rice, but if you’re just after a mild, sushi-grade bite? Trash it.