At Sushi Bar Nigirite in Shinjuku Ward, Tokyo, a 52-year-old customer from Ichikawa, Chiba Prefecture, recently discovered that what people usually consider important for sushi and sashimi may not always be right when he ordered so-called aged fish.
"I had thought that freshness was the key for fish," he said as he tried the delicacy. "But I've changed my view. It's so wonderful how the [aged] fish's umami flavor gradually spreads in the mouth."
Aged fish refers to raw fish left for several days at low temperatures. Proteins in the flesh are broken down by enzyme reactions, which helps enhance its flavor. A similar method is also applied to aging beef.
The sushi restaurant lists fish names and the number of days they have aged on its menu. On the day of my visit, for example, the menu board showed Oku-Hyuga salmon, a salmon trout from Miyazaki Prefecture, had been aged for eight days and ishigakidai spotted knifejaw for six days.
Since aged fish was placed on the menu in June 2018, the treat has become a signature feature for the sushi restaurant.
"Most customers order aged fish," said Keiichi Tsuchiya, 36, owner of the establishment.
Preparing aged fish usually starts with bleeding and filleting. The quantity of substances that provide umami flavors, such as glutamic acid and inosinic acid, increases when the fish is left at low temperatures.
Sushi Bar Nigirite bleeds fish by pumping water into the body via a high-pressure injector so that the flesh will not be damaged and the fish won't go rotten quickly.
Revolving Sushi Bar Kura, meanwhile, sells about 70 million plates of aged tuna a year. In November, the major chain operator of conveyor-belt restaurants added to its menu a new dish using tuna aged for 48 hours, longer than the conventional 36-hour aging period.
According to a survey by the restaurant information website Gurunavi, the number of establishments offering dishes using aged fish increased fivefold over the four years through October. Kayo Takahashi, an expert on fermented food, said the trend has been inspired not just by the dry-aged meat boom, but also by increased attention to fermented food as being good for health.
According to the government's White Paper on Fisheries, the annual amount of fresh seafood purchased per capita nearly halved to 7.8 kilograms last year from its peak of 14.3 kilograms in 1993. In a bid to stop consumers from turning away from fish, the fisheries industry is coming up with countermeasures.
For example, a cooperative association of fishery products intermediate wholesalers based in the Kawasaki Hokubu Market in Kawasaki last year began selling aged fish fermented using an "aging sheet" to which mold spores are attached. The sheet was jointly developed by Meiji University and a start-up company. When fish flesh is wrapped in this sheet, the meat does not go bad even after about three weeks and gives off an aroma similar to that of milk or nuts, according to the association.
"As refrigeration technology has advanced, we now can eat fresh sashimi anywhere," said Kosuke Nakaoka, an official of a fishery products intermediate wholesaler at the market. "Freshness alone cannot be a selling point anymore."
The Kawasaki municipal government, which aims to make aged fish a new local specialty, in October added the product to its list of gifts given in return for donations made through the furusato nozei tax donation program.
The town of Mihama, Fukui Prefecture, is also among municipalities that are highly interested in aged fish. The coastal town touts a specialty called heshiko, a dish traditionally prepared by fishermen for which mackerel is fermented in rice bran. Last year, the town registered a term meaning "Mihama's aged fish" as a trademark, and it aims to promote local fishery products under the label in cooperation with an izakaya restaurant in Tokyo and a local entity.
Don't try this at home
Aged fish has taken root in Japanese food culture as a nonperishable dish. For example, kabura-zushi in the Hokuriku region involves inserting salted yellowtail and other ingredients into cuts on salted turnips to ferment, while funa-zushi around the coastal areas of Lake Biwa in Shiga Prefecture consists of salted carp fermented together with rice.
However, there are some points to be noted if you are thinking of aging fish at home.
The speed of aging greatly varies among individual fish. They are susceptible to temperature changes caused when refrigerator doors open and close. They could go bad before being aged if they have contact with other foodstuffs in the refrigerator.
"Fish have many microorganisms on the surface and in the gills, and the muscle decomposes very quickly," said Prof. Masao Yamazaki of the Tokyo University of Agriculture. "To prepare aged fish, delicate techniques are required such as fish bleeding, so it is risky to try to make aged fish at home."
Read more from The Japan News at https://japannews.yomiuri.co.jp/
