Tenderloin

Marbling is scored at one cross-section. Japan reads a face cut between the 6th and 7th rib, the United States between the 12th and 13th, and neither system goes back and re-scores the tenderloin, the chuck or the round. The carcass takes a marbling verdict from that single face, and every cut off that animal is then sold under it.

So an A5 tenderloin is genuinely from an A5 carcass, and it was also never separately assessed for marbling. Both are true, and sellers tend to say only the first. The tenderloin is typically less visibly marbled than the rib or the strip loin, and that is normal rather than a sign the grade was misapplied.

The tenderloin is the psoas, a muscle that sits tucked inside the loin and does very little work. Muscles that work less stay finer-grained and more tender, and they also tend to carry less intramuscular fat. Tenderness and marbling are close to a trade-off along the animal, and the tenderloin sits at the tender end of it.

That is the whole reason the cut is prized, and in Wagyu it produces an unusual result: a texture very few other cuts reach, with less of the richness that Wagyu is bought for. Whether that is worth the highest price per pound on the menu is a genuine question rather than a rhetorical one.

Treat the grade as a fact about the carcass and ask separately what the tenderloin itself looks like. A seller showing the actual cut, or quoting a marbling description for it rather than for the animal, is telling you more than one quoting only A5. Photographs of a different cut from the same programme are not evidence about this one.

Japanese menus write it as ヒレ, hire. It is the same muscle sold in the United States as filet mignon or tenderloin, though portioning and trim differ by seller, and a chateaubriand is a centre-cut portion of it rather than a separate thing.

One last practical note. Because the tenderloin carries less fat than the rib or the strip, it is the Wagyu cut least forgiving of overcooking: there is not much intramuscular fat to keep it succulent once it is past temperature. Follow the USDA guidance for whole beef steaks, 145F with a three-minute rest, and take it off early rather than late.