Food & Drink

Aged Sushi Has Become A Keyword For Top Sushi Chefs

There are approximately 23,000 sushi restaurants in Japan and it is a $13 billion industry. How do you differentiate yourself from other restaurants in the fierce competition? 

One of sushi chefs’ keywords is jukusei sushi or sushi made with aged fish. It sounds like an oxymoron – we have firmly believed that sushi must be made with the freshest fish possible. However, in the last 10 years or so, forward-minded sushi chefs began aging raw fish for even up to several weeks and sushi connoisseurs are following them.  

It is totally safe to eat that “old” fish. Also, aged fish is not stinky. Aging may sound alarming as it triggers our image of funkiness from fermentation. But aged sushi is not the same as fermented sushi. The history of Japanese sushi began approximately 1,200 years ago. The original form of sushi was made by fermenting fish with rice, salt and natural lactic acid and was served to the nobles. This type of sushi still exists as a regional specialty, such as narezushi, which is known for its sharp odor.

On the other hand, the more modern style of sushi called Edomae sushi, including aged sushi, was born in the 18th century and does not involve fermentation. Therefore, it does not carry any strong flavor. 

The purpose of aging fish is to increase umami. Umami is the fifth taste after sweet, salty, sour and bitter. Umami is a Japanese term, but it is ubiquitous globally from Italian parmesan cheese, American bacon, Mexican mole to Asian fish sauce; basically, it is the rich savoriness in your mouth. (Umami was scientifically identified by the Japanese chemist Kikunae Ikeda in 1908.)  

Right after fish is caught and killed, an energy-carrying molecule in the cells of all living things called ATP (adenosine triphosphate) is broken down and converted to inosinic acid, an umami-producing compound. Depending on the type of fish, the level of umami can dramatically increase by being aged. 

But the chef has to know exactly when to stop the process to avoid inosinic acid turning to another compound called hypoxanthine – that is when the fish starts rotting. 

That is why aging fish is an extremely laborious process: carefully applying preservative ingredients to the fish such as salt and vinegar, meticulously controlling moisture and temperature of the environment, relentlessly checking the conditions for the right timing to stop aging, which widely varies depending on the type of fish and each catch. 

Eiji Ichimura, the sushi master at Ichimura at Uchu in Lower East Side, Manhattan, is one of the chefs who are passionate about aging fish in the U.S. 

He has spent the last 50 years making sushi. “All through these years, I experimented with new elements and different styles, but they did not lead me to where I wanted to be. In the end, I came back to how to maximize the potential of fish.  Aging fish is the best answer to my pursuit of ultimate deliciousness.”    

For example, his scallops may be aged for five days. Kohada, a popular silver-skinned fish that is highly perishable, can be a week old. His bluefin tuna is around two weeks old. 

And the results? His Michelin two stars prove the effectiveness of the aging process.  Take his squid, for instance. It is opulently sweet and the taste lasts longer in your mouth, thanks to the intensified umami after aging.     

Another chef who uses the aging process is Junichi Matsuzaki of Noz 17, a new sushi bar in Chelsea, Manhattan. He started aging fish four years ago when he joined the Michelin-starred Sushi Noz in the Upper East Side. “Sushi Noz’s executive chef Nozomu Abe selectively uses aging techniques and I was inspired,” says Matsuzaki. “Edomae sushi inherently involves aging fish. Edomae was born to serve fish just caught off the Tokyo Bay. Back then there was no refrigeration system, which naturally led sushi chefs to come up with various preservation techniques. Simultaneously, they found that aging could improve the taste of fish. So it is normal even for modern sushi chefs to mature fish for a few days. To me, it totally makes sense to try to bring out fish’s peak flavor by extending the aging period,” he says.     

To enhance aged fish’s elevated umami and luscious mouthfeel even further, Matsuzaki uses akazu or red vinegar for his sushi rice. “Red vinegar is made with sake lees, the leftover from sake production, which is also full of umami.”  

You may find aged fish outside sushi restaurants as well. Isao Yamada, executive chef at Kaiseki Room by Yamada in Midtown, Manhattan, serves multi-course traditional Japanese dishes in creative style.  He says, “Umami is an essential element of Japanese cuisine and every chef strives for maximizing it on his or her plates.” For his sashimi course, he may serve 10 day-old yellowtail, for instance. Yamada, an avid fisherman, says, “the freshest fish just caught off the sea and carefully aged fish offer very different experiences of our guests and I would love to serve both. As a chef, it is definitely worth spending time and energy to age fish.”


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