The pros know that stress-free killing (Ikejime) 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.

TYPES OF EDO-STYLE PREPARATIONS

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


We hope this information will be helpful.

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.

How to Jukusei? (How are sushi ingredients matured?)

In order to mature seafood, after completing advance preparations (removing the head and internal organs then washing thoroughly; all blood must be removed), more than adequate considerations must be made for the fat content of the fish and management of the bodily fluids. Specifically, this includes processes like dry aging at a low temperature, removing moisture using salt, utilizing enzymes and fermentation, wet aging by putting the item in a vacuum pack, and wrapping in aging sheets, which were developed thanks to Foodism. These processes may be used alone or in combination, whichever process is most suitable for the fish.

In the initial stage of ‘jukusei’ (maturing), the increase in inosinic acid (the umami component) improves the taste. After that the inosinic acid starts to decrease, and once the long-term maturing stage (two weeks or more) starts, free amino acids such as glutamic acid and aspartic acid really start to affect the flavor. This has all been learned in research.

Let’s take a look at specific aging methods.

For example, for white flesh fish, a somewhat high amount of salt is sprinkled on the fish before it is stored in a refrigerator set at 3 to 4℃ with a humidity of at least 85%. The fish is not wrapped at this time. The fish is flipped over 3 to 4 times a day so that the moisture is extracted evenly. Several days later, the salt on the surface of the body and the body fluids that have seeped out are washed off with water (or thin saltwater). The fish is then wrapped in paper towels and then plastic to avoid contact with the air, and it is stored in a refrigerator at 1 to 2℃. Once the chef deeps the fish is ready, it is trimmed. Excess moisture is removed and then the maturing process continues.

We would like to take this time to point out that fish like Tai (Red seabream) and Buri (Japanese amberjack) are clearly more delicious when matured. However, when farmed tai and farmed hamachi are matured, the scent of the feed they were raised on comes out, so these are better eaten fresh, as sashimi, instead of maturing.

Blue-backed fish like Aji (Horse mackerel) and Iwashi (Japanese sardine) are also not suitable for maturing. Blue-backed fish lose their freshness quickly and judging the maturity is extremely difficult. Furthermore, if the fish is matured without sufficient advance preparations, bacteria breed in the remaining blood and organs. This may cause food poisoning.

These fish can be matured using the following method. The fish is put in salt-ice (water cooled with ice and salt) as soon as it is caught. It is sent to the sushi restaurant in this state and left in the refrigerator to rest for several days. Unfortunately, what happens after this is apparently a trade secret.

The easiest method is to wrap in an aging sheet and put it in the refrigerator. After that the chef trims the fish, checking the state of it. An aging sheet is a cloth made from purely breeding a ‘mold’ that is harmless to the human body, and putting cultures of its recovered spores into the cloth. Originally, it is intended to be used to age meat, but it’s just started to be used for seafood too.

Finally, in a method used for ages by sushi chefs, the akami and toro (tuna) portion are taken out and the chiai* portion is removed to be matured. This is then wrapped in paper towels, put into a plastic bag in order to prevent drying out, then put into the refrigerator to rest. The temperature setting is the most important part of this process and, obviously, this is an industry secret. The chef needs to check the state of the tuna (for example whether the white lines are soft and whether the oil has risen), and any discolored portion is trimmed. After that it is refrigerated. This process is then repeated.

*“Chiai (血合い)” is the part with the most veins, so it is a dark red color. It has a strong odor of blood and has multiple times the acidity of the lean meat, so it is not used as a sushi topping.

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


We hope this information will be helpful.

Revision date: June 2, 2020

 

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.


We hope this information will be helpful.

Revision date: August 20, 2018

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Tuna is allowed to rest before it is used.

Once a bluefin tuna is caught, it arrives in Tsukiji fish market within a day or two. However, that fish is not used as a sushi topping that day. No mater how good the tuna is, it starts out very stiff and is not in a state where it should be eaten. The meat is hard and the white muscle lines are left in your mouth. The odor and acidic taste of the red meat is strong and the unique sweetness of the fish is nowhere to be found. After it has rested the muscles soften, bringing out the fat.

Then, when the sushi chef gets the tuna, he first separates the red, lean meat and the fatty toro portion, rewraps them separately and, seals them in plastic and puts them on ice. Next is waiting for the “young” meat, not yet suitable for eating, to mature. The number of days the fish will be rested depends on the size of the fish and the temperature. The smaller the cut and the warmer the temperature, the shorter the rest time. Generally the time is from 3-14 days.

This “young” fish not ready for consumption is a fresh, deep color but as it matures the color darkens, the fat is brought out and becomes a fleshy color. Proper care must be taken because if it’s rested for too long, the color changes too quickly.


We hope this information will be helpful.

Revision date: August 13, 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.  Also, on the dorsal side there is a part that produces chutoro called wakaremi. This part is also complex with white lines throughout that we want to avoid eating. 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: July 16, 2020

Strong belief that fish is only about freshness

In some cases, the strong belief that fish is only about freshness, may prevent you from tasting the true value of the fish. For example, slicing up a fish that was just swimming, in front of the customer. The umami flavor is weak at first so while the texture is tough (a unique, crunchy feeling), the flavor is lacking. But the idea that freshness is equivalent to deliciousness continues still. This is a typical case of faith in freshness overtaking the actual taste.


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Revision date: April 16, 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

Isn’t it true that fish is all about the freshness??

It’s a well-known fact among professional chefs that some fish don’t rely solely on freshness. Of course there is importance in freshness, but that’s just one element. It’s generally understood that flavor and taste improve with time (maturity).

The umami* found in the meat of the fish is essentially inosinic acid and glutamic acid. After a certain amount of time has passed after a fish has died, the body stiffens and not long after that the rigor lets up. The inosinic acid, which the umami is composed of, comes after the fish has stiffened. It then accumulates in the process of the body relaxing. This is the same in beef and pork in which there is no umami in the meat unless it is hung and matured for a time.

Therefore, ikizukuri sashimi that is still twitching usually won’t have the taste or depth of umami. However, the firm texture of sashimi is also an undeniable enjoyable aspect. It is not all about the umami.

*Glutamic acid, Inosinic acid and Guanylic acid are representative components of umami. Guanylic acid is found in kelp and vegetables (tomato, Chinese cabbage, green tea, etc.) as well as Parmesan cheese, inosinic acid is found in fish (bonito, macheral, sea bream, etc.) and meat (pork, chicken, etc.) while Guanylic acid is abundant in mushrooms (especially dried shiitake mushrooms).


We hope this information will be helpful.

Revision date: July 17, 2017