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


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Revision date: June 2, 2020

 

What makes a “good” sushi restaurant?

It is probably cutting fish just before serving. For a big size fish, keep its skin on the meat during the process of preparing and cutting into half, and at every serving use sogigiri* as much as customers eat. Protected by the skin, the fish flesh will expose to air for the first time as it is cut. The skin blocks the oxidation process significantly because the fat in fish centers right  under the skin in general. Needless to say, even with any amazing fish, it loses flavor if the fat gets oxidized.

*Sogigiri-A method of cutting which makes a slice thinner with a greater surface, by holding the knife diagonally and cutting in line with the cutting board. Usually used for white fish with firm flesh because it is easier to be eaten when served thin.

Hirazukuri-A method of cutting which gives thickness to each slice so that the texture of sashimi can be enjoyable. This is used for akami like tuna.


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Revision date: April 1, 2020

What are side dishes at sushi restaurants?

A side dish at a sushi restaurant is a wonderful experience. It’s best when they serve seasonal sashimi, grilled items, or sake and fish that are fit well in sushi restaurants, but some places serve dishes that are easily mistaken as the main dish, such as deep sea bass hot pot. Eating an exaggerated dish like that doesn’t leave much room for sushi. Side dishes at sushi restaurants are only meant to be an appetizer to the sushi. A sushi restaurant that serves small dishes that don’t fill you up, but help tickle your appetite, transitioning into the sushi pieces, is a good restaurant.


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Revision date: March 2, 2020

A technic to freeze tuna is quite amazing!

Once tuna caught in the open sea is processed by draining its blood on the ship, it is flash-frozen at ultra-low temperatures (-60℃). Ultra-low temperatures stops the enzymatic hydrolosis of protein, oxidation of fat and cultivation of microorganisms so it can be stored over a long period of time. The process can prevent discoloration for over two years and maintain a freshness worthy of being served as sashimi. Therefore, skillful sushi restaurants mature the thawed tuna in the refrigerator for about one week to attain the perfect balance of umami and change in color.


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Revision date: February 4, 2020

Are Hamachi and Buri the same thing?

In the United States and other countries, “buri : right image” is called yellowtail, but this word refers to fish like “buri” and “hiramasa” and actually can be applied to a large number of fish. Actually, it isn’t far off since a layman can’t tell the difference between a “buri” and “hiramasa” just by the pretty yellow line on the side of the fish’s body.

In Japan, “buri” is the most well-known fish that goes by different names depending on its stage in life (shusse fish). Actually “buri” has many different names even depending on the region you are in. For example, in the Kanto region, it may be called wakashi (0 to 30 cm) → Inada (30 to 60 cm) → Warasa (60 to 80 cm) → Buri (80 cm or more), and from Kansai on further west, it is called, Tsubasu (0 to 30 cm) → Hamachi (30 to 60 cm)→ Mejiro (60 to 80 cm) or Buri (80 cm or more).

This is where the term “hamachi” came from West of Kansai, full-grown buri, at about 30 to 60 cm is called Hamachi. In other words, Hamachi is a young buri.

Of course, it’s not that simple. You can get hamachi sashimi at grocery stores all over Japan, all year long. Hamachi is not only used from Kansai on westward, it is also used at grocery stores throughout Japan. This may lead you to believe that hamachi is a different fish and not the same as buri, but you would be mistaken.

Behind the curtain, buri cultivation is thriving in Japan (and throughout the world). More than 80% of the buri on the market is said to be farmed. Because it is not apparent by appearance whether the buri was raised in the wild or by aquaculture, the wild-raised fish is called buri by market affiliates in order to make it easier to understand. That means farmed products have come to be called hamachi.

Also, in the Setouchi region, people preferred to eat the young hamachi rather than the adult buri. Kagawa Prefecture became the first in the world to successfully cultivate hamachi in 1928, and that is what led ‘hamachi’ to become synonymous with ‘farmed fish’. Of course, that would be one reason that people call farmed buri, hamachi.

As an aside, three cousins (closely related species) of buri are often used as sushi toppings in sushi restaurants. In the Fish Name Dictionary, the translations of these cousins are Goldstriped amberjack (Hiramasa : right image), Greater Amberjack (Kanpachi), and Japanese amberjack (Buri). Sushi University also adopts these terms.

But if you dive deeper into the fish name dictionary,
Hiramasa is known as amberjack or yellowtail or hiramasa kingfish. Kampachi is known as amberjack or yellowtail. Buri is known as… you guessed it: amberjack or yellowtail.

When lumping them all together, they are called yellowtail, as is common in the U.S.

I’m sure you’re interested in the price, and while the price of the seasonal winter buri varies, it is generally around $10-20 per kilogram. Since there is very little distribution of hiramasa, the price is said to be about double that of buri. The price of kampachi : right image is somewhere between that of buri and hiramasa. These prices refer to the wild-caught fish.

Finally, if you eat and compare buri, kampachi and hiramasa in sashimi form, most people can’t tell the difference in fat distribution. When made into sushi (buri sushi, hamachi sushi, hiramasa sushi, kampachi sushi), the sweetness of the fat and the flavor of the fish emerge splendidly, and the taste of each fish becomes distinct and obvious. Even the still-developing inada, with very low fat content, is used as a sushi topping and its refreshing taste is unforgettable. This showcases both the depth and greatness of Edomae (Edo Style) sushi.


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Revision date: April 24, 2020

Why did the world’s best sushi restaurant strip of its three Michelin stars!?

Even Japanese people can be overwhelmed by the somehow special atmosphere when they sit down at the sushi counter. This continues even when starting to eat. Other customers are concentrating on eating, quietly. You kind of get the feeling that if you utter anything, you will be asked to leave. If you don’t end up mustering up the courage, you just end up paying the high price for your meal and going home without much more to say of the evening.

Eating sushi at a counter is not inherently this dull. So why do sushi meals so often end up this way? The problem is knowing so little about the sushi, and feeling like you’re the visiting team on the field.

For example, it is taboo for new customers to take the seat positioned directly in front of the sushi chef. This is a special seat reserved for regulars. Even if the seat is empty, a newcomer will be shown to a seat in the back. This is an unspoken rule.

Contrary to their countenance, most sushi chefs are actually friendly and experts in the art of conversation. They especially value the back and forth with regular customers. For example, they have a keen memory, and can reiterate to the customer that their last visit was on the way home from a baseball game and they ordered a second helping of Chutoro fished in Oma. Of course this pleases many customers. A master sushi chef prepares sushi while standing in front of the customer. If there was to be no conversation with the customer, they can make the sushi back in the kitchen and have it served. Sushi restaurants are a place for conversation.

The customer ends up not remembering which fish they ate. For example there are very few people who can name the order of the 15-piece Omakase course they ate. You may be sure you ate tuna. But where was it caught? Was it the belly side or the back side? How long had the fish been matured? To be a bit more frank, how much did it cost? If you ask the chef these questions, next time you visit, you’ll be able to compare different taste based on the fishing location. Knowing the difference in taste based on the part of the fish, and difference in flavor depending on where it was procured, and different taste depending on the preparations will certainly improve your sushi literacy remarkably. It will also lead to a better awareness of your own taste preferences.

But there are limitations to the time allowed for personal conversation. For example, in a normal 2-hour Omakase course, there may be five minutes or so available for conversation. It might not sound like much, but that is also the amount of time allocated to regular customers. Newcomers often can’t find a time to get a word in and end up with only the initial greeting, which takes about 10 seconds.

Of course that’s for Japanese customers who speak Japanese. What about foreign customers who cannot speak Japanese? First of all, conversation is impossible, so this cuts the enjoyment factor of the sushi restaurant in half. But the sushi is delicious, right? Perhaps, but you’ll end up satisfied with the small-world view cultivated for you by the media, limited to whether or not the fish is fatty, or if the meat is fresh and firm. This is something you can experience anywhere that sushi is served in the world.

What we offer is a totally different experience.

You get a seat in front of the master sushi chef, a knowledgeable interpreter is seated by your side, and the Omakase show is presented right in front of you. The obliging chef explains each piece of sushi as you eat with a gentle demeanor. He will also answer any questions you think of on the spot. You won’t be able to say that you don’t know what you ate. We prepare a translated list of your Omakase menu. You are also welcome to take pictures whenever you’d like to preserve the enjoyable memory. All you need to do is forget time and immerse yourself in the Edo-style sushi, one of the staples of Japanese food culture.


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Revision date: November 27, 2019

What is the ideal temperature for sushi toppings?

Tokyo Health Centers stipulate that refrigerated cases where sushi toppings are stored should be kept at 5℃ or lower. This is to maintain the temperature of the toppings at below 10°C at which point bacterial growth is slowed.

However, sushi chefs will remove the topping from the refrigerator and leave it standing out for a while (in the case of tuna, the fat will melt at around 23℃). They do this because if the topping is cold, it becomes difficult to taste the essential nature of the fish. The temperature of the shari is best at human skin temperature (around 36℃) to maximize the taste and sweetness of the rice. However, the ideal temperature differs very slightly depending on the topping.

For example, conger eel which is often lightly grilled or prepared in another, similar way, should have a slightly higher temperature (around 42℃) than the shari, and kuruma prawn, which are boiled, should be the same temperature as the shari.

Overseas, there are laws that state that sushi must be served at 10℃ or lower. This ignores that sushi is best enjoyed at skin temperature. Serving it straight out of the refrigerator makes it no better than purchasing takeout sushi from the supermarket.


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Revision date: November 18, 2019

Why does it taste a little bland when you had tuna at high-class sushi restaurant?

Tuna at top-end restaurants is light in flavor. Its Akami (red meat) has an indescribable acidity with a delicate harmony between the shari vinegar, the nikiri soy sauce, and wasabi. However, on the other side of the coin, it feels almost like a waste to eat it without a sense of luxury. Of course tuna with delicious akami, also has delicious fatty tuna (toro). And you’ll never get tired of it. It would be easy to polish off 10 pieces as a light snack. Contrary to popular belief, it’s not the high fat content that makes it so easy to eat. However, it is because of that popular belief that many people feel that the big chain store farmed fish with lots of fat is more delicious than luxury natural fish.

 


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Revision date: April 16, 2019

What is Red Snapper the same as “Tai” (Sea Bream)?

In the United States, Sea Bream is often called a Red Snapper. However, strictly speaking, this is not correct.

Biologically, Snapper is a generic term for all species in the snapper family (Lutjanidae). Over 100 different species of snapper inhabit tropical coastal waters. Red snapper is mainly fished in the Gulf of Mexico.

So, what is the fish that Japanese sushi restaurants call “tai”?

They say there are over 300 different species of fish with “tai” in the name, making up 10% of Japan’s fish. When we say “tai” in Japanese, we are referring to “madai” or red sea bream. Red sea-bream is categorized in the “madai” family (Sparidae).

Incidentally, relatives of the sea bream often served at sushi restaurants include red sea bream (madai), crimson sea bream (chidai) and yellowback sea bream (kidai). While “kinmedai” (Splendid alfonsino) and “amadai” (horsehead tilefish) have the name “tai/dai” in them, they are not part of the same family as “tai”. Splendid alfonsino is a type of deep-sea fish.

Red sea bream and red snapper look similar, but when served as sushi, their texture and flavors are entirely different. So if you come to Japan, please try and eat natural madai. There is no “zatsumi” (overpowering bitterness) and it has a slight sweetness to it. This is the taste of tai, known as king of the white fish. Just for your own reference.

Related Contents

https://sushiuniversity.jp/visual-dictionary/?Name=Red-seabream-(Tai)


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Revision date: April 28, 2020

Why do we use the counter “kan (貫)” for sushi?

When you sit at the counter and order nigiri a la carte, they will come out in pairs.* There is nothing wrong with counting these in the regular Japanese way “ikko,” “niko.”

*It is said that nigiri-sushi in the Edo period was bigger than it is today, and too big to eat in one bite. In the Meiji period, the custom emerged of splitting this one big portion into two to make more easily consumed portions, and this is why it is common to get sushi in sets of two. However, nowadays making one piece of nigiri-sushi at a time is not very efficient. We think it’s actually easier for the sushi restaurant to make them in sets of two. Of course, you can order them one by one.

But the sushi restaurant won’t count them like that. Formally, sushi is counted in this way: Ikkan (one), Nikan (two).

We have absolutely no idea where the custom of using the “kan” counter came from. It’s also not clear when use of that counter for sushi started.

Of course, there are theories. For example, there is a theory that back at a time when a single unit of money was called “kan.” The price for one piece of sushi was around 1 ‘kan’, and the counting method gained popularity. There is another theory that one sushi roll was counted with the counter for roll “巻” (also pronounced “kan”), then a different kanji was used for it later. However, these are just theories that were created after the fact and the mystery remains unsolved.

Even if you ask the owner of a sushi restaurant, they’ll probably cock their head to one side, think for a moment, and tell you that the “kan” mystery may never be solved.

Sushi rolls wrapped in seaweed rolls are counted in units of 本 (hon/bon/pon) in the wrapped state, and when cut with a knife, the units change to 切れ (kire). While these units are fairly straight-forward for Japanese language speakers and easy to understand, only the enigmatic 貫 (kan) remains a mystery.


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Revision date: April 29, 2020

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Do you know that there are rankings for negitoro (minced tuna)?

The original negitoro is made from medium fatty tuna or nakaochi* chopped up finely with a knife and then mixed with chopped green onions on top. But the tuna may be switched out with filler, leading to a variety in quality of the negitoro available.

First of all, the lowest in the ranking are the offcuts of tuna that can’t be made into sashimi (mainly Yellowfin or Albacore tuna) and this is mixed with vegetable oil and minced. The type of onion used is normally green onions. You can pick this type out because it will be whitish in color. This version is normally served at conveyor belt sushi.

The medium quality uses the nakaochi of cheap Albacore tuna or Swordfish.

High quality negitoro uses the nakaochi of Pacific bluefin tuna or Southern bluefin tuna. Sometimes the green onion sprout is then rolled up inside. If you have a chance to try negitoro in Japan, we recommend you try the top quality options without a doubt. One piece will probably cost around $15 USD. But that’s the price for the real thing!

Finally, let me introduce some negitoro trivia. There is a lot of flesh on the middle bone (spine) and the surrounding area for tuna and the like. This is called “nakaochi*”. Scraping the meat from this area surrounding the spine is known as “negitoru”, which is where the word “negitoro” comes from. In other words, the name “negitoro” is not actually from the words onion (negi) and tuna belly (toro).

What is negitoro like at Sushi restaurants?

Originally, the meat from the middle cut or in between the bones of the tuna was used for negitoro. In order to get meat from these parts, the chef would have to purchase an entire tuna, or buy the cut that includes the mid-ribs. However, both of these purchases are difficult for a single sushi restaurant, so now the chef chops the meat from the body with a butcher knife until it forms a paste that is sticky and smooth from the fat in the tuna. This paste is used for negitoro.


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Revision date: July 21, 2020

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What is Kakushiaji?

Kakushiaji refers to a technique where a single seasoning (For example, sugar, vinegar, soy sauce, salt, etc.) is added to a dish. The Kakushiaji contrasts with the finished dish’s flavor, and is added in an amount too small to notice when served. This produces a clear improvement in flavor.

Examples include adding a little salt to heighten sweetness, or adding a little vinegar to a simmered dish. Sometimes these combination of flavors can be quite surprising, like adding a touch of chocolate to a curry.


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Revision date: November 7, 2018

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

Is the handmade ginger in quality sushi restaurants free?

The ginger served in sushi restaurants is called “gari”. There are people who just chomp down the gari since it’s all free.

However, in certain prestigious restaurants where the gari is handmade, it does end up on the bill. This is because considering the time and ingredients that go into making the gari, the restaurant will be losing money if they don’t charge for it.

 

However, most sushi restaurants purchase their gari from companies that specialize in it. These mostly include pickling manufactures that have expanded to China or Southeast Asia and have factories there.

When made at these factories, large amounts of ginger is soaked in the stock solution, creating gari in bulk. The quality has improved greatly over the years, but often the fibers are crushed making it soggy, or the gari is stained from ume vinegar.

On the other hand, homemade gari and gari made in Japan is flavored with vinegar and salt while sugar is used sparingly as a subtle flavoring. Handmade gari is crunchy and chewy. The color is also the original pale yellow of ginger.

And during the fresh ginger season at the beginning of summer the price of fresh, domestic ginger jumps up to thousands of yen per kilogram. Since ginger has a high water content, it can be wrung out to reduce 1kg of ginger down to 300g. Making delicious gari by hand costs money. It is also a daunting task of making a year’s worth in advance. Once it’s done there has to be a refrigerator dedicated to storing only the gari.

When you put it that way, homemade gari is far more expensive than its imported equivalent. Providing homemade gari is one of the things that sets sushi restaurants apart from each other. Of course even if you’re not charged for the gari, eating too much will affect your sense of taste for the meal.


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Revision date: October 8, 2018

What is the difference between “鮨,” “鮓” and “寿司” (all ready “Sushi”).

As far as I know, there are three ways “sushi” is written on sushi restaurant curtains in Japanese kanji characters: 鮨, 鮓 and 寿司.

Do you know the difference? Most Japanese people don’t know the answer to this question.

Broadly, in the Kanto area 鮨 is generally used while 鮓 is more common in Kansai. 寿司 is used commonly everywhere in Japan.

However, of the three, only 鮨 and 鮓 are seen in ancient Chinese literature. 鮨 was seen as a dictionary entry as early as the 5th to 3rd centuries B.C., and it’s origin is described as combining “fish” and “shiokara” (briny flavor) resulting in the term 鮨.

On the other hand, in A.D. 1st to 2nd century dictionaries, “鮓” appeared, and is explained to depict “a storage container for fish.” Toward the end of the second century 鮓 was used for the term “narezushi”.

But around the third century, the briny meaning of 鮨 and the term “narezushi*” written as 鮓 started to be used interchangeably. That is how the words were imported to Japan.

In Japan, the character “鮓” was often used in literature from the end of the Heian era to the end of the Edo era. Eventually the use of “鮨” was revived during the Meiji era (for unknown reasons). It was a natural transition that Kanto came to use “鮨” and Kansai came to use “鮓”.

Incidentally, the kanji “寿司” was created from the phonetics. Its use for celebratory occasions became commonplace throughout Japan.

*”Narezushi” is the primitive version of Japanese sushi. It means covering seafood with salt and then soaking in rice for a few years as a form of lactic acid fermentation, which brings out the acidity.


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Revision date: April 29, 2020