Naka-ochi and different species of tuna
Tuna sushi is more expensive than salmon. Since we are not an official sushi restaurant, we do not bother purchasing tuna meat. Sushi fish suppliers typically buy their fish from Billingsgate market by weight and debone and cut it into different sections.
During the cutting process, the bits of tuna meat that have been scraped off the bones are called naka-ochi, meaning “inside drop.” These are cheaper than a chunk of tuna meat because the odd bits and pieces do not make for pretty, presentable sushi. Often, a sushi chef will mince this meat and mix it with spring onion to make Negitoro sushi.
We first ordered naka-ochi from the supplier Jo Showa and then from Atariya. When it arrives, it has a vibrant red color due to its freshness, and we try to use it up before the characteristic browning of tuna occurs.
The interesting point to note is the species of tuna from which this naka-ochi comes. Jo-Showa was a mix of Yellowfin tuna and Atlantic bluefin tuna (honmaguro, or real tuna). You can distinguish between the two by their color; Yellowfin tuna has a translucent red color, whereas Atlantic tuna is cloudy red. We were lucky to find some fatty toro tuna in there, which is seen by its more pinkish color. A toro tuna comes from Atlantic tuna, as the Yellowfin rarely has a fatty part.
The flavor of the two species also differs. Yellowfin tuna has a less tuna-like flavor, which is less distinct than the strong metallic, blood-like flavor of Atlantic tuna. Whether someone likes this taste is a matter of preference. Our chef Tonton gets excited when she sees Atlantic tuna because it is a rarer ingredient and her favorite.
Next, the naka-ochi from Atariya was 100% bluefin tuna. It had fewer toro parts, but Tonton was elated. She ate it while talking about how expensive it has become in Japan due to tuna depletion. It was delicious, but I preferred the Yellowfin tuna. Bluefin had a metallic taste like bonito (skipjack) sashimi.
Next time you eat Tuna sushi, check out which species you may have.