The pros know that stress-free killing is the key to good flavor!

Ending a fish’s life without stress is the key to delicious flavor. When fish are left out in air, and die in agony it promotes rapid Adenosine triphosphate (ATP) degradation and increase in Inosinic acid. This is the worst way to kill a fish.

So what method can control the fish’s flavor or “umami”?

The delicious flavor of fish comes from the postmortem breakdown of ATP, which is the source of biological energy, and the generation of Inosinic acid, which is the component of the umami. Rigor mortis after the fish has died, progresses with the decomposition of ATP. When oxygen supply is cut off after death, energy required for muscles to move is no longer supplied, so flexibility of the muscles is lost and the body starts to contract. This is postmortem rigidity. This state depends on the fish, but it is the lowest point for flavor and after that the fish is managed at an appropriate temperature to increase the Inosinic acid.

This method has been the norm among sushi chefs who didn’t know about the mechanism that produces umami. Since long ago, the daily routine was to purchase fish that were killed first thing in the morning in the market, then increase the umami by keeping the fish in a refrigerator with a controlled temperature for 12 to 48 hours. Nowadays, the method has become common practice among fisherman, distributors and fish handlers at the market.

Now I will explain a number of methods that maintain peak flavor.

Ikezukuri means to take a fish that’s swimming in a tank at the restaurant, and immediately making sashimi after killing it, while the meat is still super fresh. In this state, there is no Inosinic acid, but there is quite a show with movement still in the fish and this preparation method gives the best-tasting texture.

Nojime* means using a massive amount of ice to suddenly reduce the temperature, resulting in death of the fish, either at the fishing site or at the local market. This method is used for small, cheaper mass-market fish that are caught in large amounts. Nojime starts with a reverse calculation for flavor from the day after fishing, but if the process isn’t thorough or there are any deficiencies, the fish won’t stay as fresh, so detailed care must be taken in temperature management.

Hamajime* means to cut the spinal cord at the production site, drain blood and spinal fluid, then pack in ice from afternoon the next day and wait for the peak flavor, which will be about two days later. That’s when the seafood is shipped to make it to make it to the consumer auction the next day. As time passes, inosinic acid is generated and the aim is to use the fish in sushi at peak flavor.

Ikejime is used so that the peak flavor will be reached during afternoon and evening business hours. The spinal cord of the live fish is cut and spinal fluid drained at the early morning market. This results is a firmness from the remaining ATP, and delicious flavor from the Inosinic acid that is generated as time passes. After some time has passed, even fish for which Ikejime is applied, can reach the same state as Hamajime if used after being refrigerated for one to two days, in order to maximize the Inosinic acid generated. Of course sushi chefs find their own balance of firmness in meat or added flavor, and incorporate this balance for the optimum combination with their shari in each piece of sushi.

Finally, maintaining freshness by using Ikejime, has become common practice overseas, and the term “Ikejime” has also become standard among the fishing industry. There are many websites that go into further detail on Ikejime, which you can reference from the links below.

*At markets in Japan, the term “kill” is not used for living fish, instead the word “shimeru” meaning to “close” or “tighten” is used. This expression is thought to have come from the sentiment of showing respect and appreciation for all living beings, not only humans.

Related Contents

http://fr.gaultmillau.com/news/premiere-poissonnerie-ikejime-a-paris

https://elisabethscotto.com/2016/02/27/ikejime/

https://www.huffingtonpost.fr/2018/12/18/le-poisson-ikejime-la-technique-ancestrale-venue-du-japon_a_23617381/

https://www.lemonde.fr/m-gastronomie/article/2017/04/27/l-ikejime-cet-art-japonais-qui-sublime-le-poisson_5118590_4497540.html

https://guide.michelin.com/sg/en/article/dining-out/what-is-ike-jime

https://www.1843magazine.com/food-drink/ikejime-a-humane-way-to-kill-fish-that-makes-them-tastier


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Revision date: May 1, 2020

What is Jukusei sushi?

The fish used in sushi is generally salted or soaked in vinegar then matured for a number of days while the umami Inosinic acid component increases. This is called “Jukusei” (aging). Sushi made with toppings that have been aged in this way are called “Jukusei sushi”. The aging period depends on the type, individual size and origin of each fish, and some are even aged for over four weeks. However, the preparations are not only difficult and time-consuming, the discolored parts and inedible parts must be trimmed, so these toppings tend to be expensive. If gone too far, the Inosinic acid converts to hypoxanthine and rots. The ability to make this judgment is important. In the end, Jukusei is an evolved version of the culture of “maturing toppings” which existed in Edo-style Sushi.

Related Content

https://guide.michelin.com/en/article/features/%E4%B9%BE%E5%BC%8F%E7%86%9F%E6%88%90%E9%AD%9A

https://www.foodandwine.com/cooking-techniques/dry-aged-fish-joint-sherman-oaks


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Revision date: April 25, 2020

 

What is Umami?

Umami describes the delicious taste of savory flavor essences. For many years, people held to the belief that humans can taste only four basic flavors (sweet, sour, salty, bitter) unitil a japanese chemist named Kikunae Ikeda discovered a fifth flavor (glutamic acid) in the early 20th century.

The main umami ingredients are glutamic acid in seaweed, inosinic acid in dried bonito and meats, succinic acid in shellfish, guanylic acid in shiitake mushroom.

Many ingredients contain a wide variety of umami essences. In combination, they create a  synergistic effect which produces an even more potent savory flavor.


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Revision date: October 31, 2018

The migrating route of Inshore Pacific bluefin tuna and fishing place!

Tuna caught in the coastal regions of the Japan Sea is notable as the best bluefin tuna in January. Iki, a small island in Kyushu area is one of the famous ports for tuna.

In February and March, the tuna auction market becomes slack due to rough weather. Just a few tunas from Nachikatsuura where is also the famous port for tuna are on the market.

In March and April, tunas become thin because their eggs need many nutrients.

In May, large tuna is seldom seen in the Tsukiji Fish Market. Even if there is, its body is really thin. “Kinkaimono” which means a shore-fish is generally considered as high-class tuna, but in this season, imported tuna is useful instead.

It is said that Pacific Bluefin tunas spawn around Japanese waters between Taiwan and Okinawa in April and May. And then, they go up to fertile, north sea along the eastern coast of Japan.

In June, “Chubo” which is young and small tuna is taken hugely off the coast of the Sea of Japan. The school of Chubo begin moving northward in this season.

In July and August, tunas can be seen occasionally but their bodies are still thin. Instead, Boston Tuna which is caught in the Atlantic Ocean and nicknamed “Jumbo” is on the market. Its fresh is softer than “Kinkaimono” and it doesn’t have medium-fatty part which “Kinkaimono” has.

In September, Boston Tunas are at their best with plenty of fat on them. The best season of Boston Tuna is limited and ends in October. But fortunately, Japanese tunas come into season.

The school of tunas split up into two groups, the one takes Pacific Ocean route and another takes the Japan Sea route and both of them move northward along the Japanese Islands. Some of them reach the Tsugaru Strait where and the season of Tuna begins from September to next January. Oma town and Toi town is famous nationwide for its catch of tuna from the Tsugaru Strait. The flavor of tuna in September is still weak but it becomes stronger in October. In November, feed of tunas such as Pacific saury or Japanese common squid with plenty of fat increase and flavor of tuna also gets stronger. In December, the peak season comes around.

A catch of tuna falls off in January and it enters the final season. The temperature of sea water gets cold and feed of tuna, squids decrease and the fishing season in this area ends.


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Revision date: August 20, 2018

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What is the difference between maturing and rotting?

When fish die, stopping the supply of ATP (Adenosine Triphosphate), the source of muscle energy, the muscle fibers gradually harden. As time passes, it gently dissolves and the ATP breaks down, changing into umami components due to self-digestion. The umami created by self-digestion of ATP is “maturing” and the process after that is “rotting.”


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Revision date: July 23, 2018

What is Uwami and Shitami?

Large fish that are caught are always kept and transported on their side with their heads facing left from the port to the market and to the restaurant where they are served. The part of the fish facing down when in this position is called “Shitami” or the “bottom body” and the part facing up is called “Uwami” or the top body. The Uwami costs more than Shitami. This is because the Shitami takes on the weight of the Uwami, reducing the freshness and possibly causing cracks in the body (cracking occurs on the edges of the muscles).


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Revision date: May 21, 2018

What is “Hagashi”?

There is a part on the tuna belly called “Sunazuri” or “Zuri” (gizzards). Normally “Jabara,” with the diagonal white lines is the king of tuna, but the fatty tuna is spoiled if the white lines are left in your mouth. Instead, the knife cuts along those lines, gently removing the fish meat from them, making “Hagashi.” If the chef is not skilled, this cut will take time and extra meat is left behind. This is delicate work, making for a delicious and satisfying experience.


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Revision date: May 7, 2018

Why is freshly-caught fish allowed to age?

The most delicious time to eat fish differs depending on if it is served as sashimi, as sushi, or boiled. Fresh does not necessarily mean delicious. For example, Japanese Amberjack should be used in sashimi 3-5 days after being caught, in sushi a week after being caught and it can be used in a stew or boiled once it turns black around the edges. This is because the inosine acid, which is responsible for the umami taste, increases after rigor mortis ends and understanding the timing of the peak in flavor is up to the skill of the sushi chef.


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Revision date: March 12, 2018

Why is Zuke used for lean meat?

Zuke is one of the traditional Edo-style sushi methods. It is said that it was started in the Edo period to stop tuna from rotting when there were large amounts of the fish in the market. Now that there has been advances in refrigeration technology, it’s no longer necessary, but maturing the fish gives it a completely different taste and brings out its umami. Zuke is divided into two broad methods. Here we describe the characteristics of each.

Recently, most sushi restaurants incorporate the “Single Zuke”.

Each slice of tuna is soaked separately, so it can mature quickly. The immersion time is only a few minutes. The idea is to marinate just enough so that the tuna’s aroma remains and the soy sauce doesn’t overtake it.

On the other hand, the old Edo-style method is to perform Zuke after parboiling.

Parboiling means to wrap the fish in a wet cloth, and poor boiling water on the wrapping until the color of the tuna changes color, then turn the fish over and repeat the process. The fish is then put in ice water so the heat doesn’t go too deep in the meat. It is immediately removed once it cools so that it doesn’t get too watery. The tuna is then put in Zuke soy sauce and left to marinate for about half a day. In this method, the soy sauce only soaks into the surface part where the color changed from the parboiling, so the flavor of the tuna remains.

Both methods keep the maximum tuna flavor possible. Tuna is an essential part of Edo-style sushi. There is great diversity between sushi restaurants in the parts, marinating time and flavor of Zuke, which creates a new, original flavor when the lean meat of the tuna soaks up the soy sauce. The fattiest cuts of tuna are most popular. The lean meat has only become more popular due to a rekindled interest in zuke, but in fact during the peak of the bubble economy, there was a time when high-end restaurants in Ginza didn’t know what to do with all their leftover lean tuna meat. It’s almost unbelievable to think of it now.


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Revision date: August 1, 2017