A major cause of poor performance by sushi restaurants is that the seafood they purchase remains unsold. Instead of being served to customers as sushi or sashimi, it begins to rot and is discarded. When this situation persists, people resort to things they should not do.

It is used as a freshness preservative to extend shelf life because it prevents oxidation of perishable items by absorbing oxygen in a sealed condition. It is used to prevent the deterioration of pharmaceuticals, clothing, cosmetics, etc., so it is not a suspicious chemical, but it is used in the wrong way.

On the other hand, a factor that significantly increases performance is the use of ingredients purchased at low prices and served as overpriced dishes. For example, a food fraud is to offer a lumpfish caviar as a Beluga caviar. This is like exchanging a $1 bill for a $100 bill.

Those who believe in the goodness of human nature may find it hard to accept that such things are happening, but please take a look at the survey results below.

Oceana, a marine conservation organization, previously released a study that found that approximately 60% of supermarkets and restaurants that sell seafood in New York City had some seafood that was different from the product name. The survey involved DNA analysis of 142 seafood samples from 81 supermarkets, food stores, restaurants, and sushi restaurants in New York City. According to the survey, sushi restaurants were found to have the most fish samples that differed from the product names (76%), followed by restaurants (39%), and supermarkets and food stores (29%). The most common type of fish found to be different from the actual product was white tuna. Of the 17 samples of white tuna brought back from sushi restaurants, 16 or 94% were Escola.

By the way, what kind of fish is white tuna in this survey? White tuna does not exist. In Japan, Yake maguro, which died after being caught violently on longlines, is sometimes called so.

Overseas, however, this does not seem to be the case. Often marketed as “white tuna” or “super white tuna,” this is the common name for two species of fish, Escolar (Aburasokomutsu) and Oilfish (Baramutsu). The flesh of Escolar (Aburasokomutsu) and Oilfish (Baramutsu) are rich in taste and can be substantially cheaper than that of other fish species, leading to some vendors intentionally mislabelling it as Butterfish or Cod.

Escolar contains a waxy ester called gempylotoxin which makes up to 90% of the fish’s total fat content and gives it its characteristic texture. Despite its name, gempylotoxin is not poisonous. However, humans can’t digest this waxy substance, and consuming it can lead to stomach cramps, intestinal discomfort, and an unfortunate encounter with the toilet for some individuals.

Oilfish (Baramutsu) has been banned by the Ministry of Health, Labor and Welfare in Japan since 1970 as a food that falls under the Food Sanitation Law and is not distributed. Escolar (Aburasokomutsu) is also a member of the same family, and its sale is prohibited under the same law.

In South Korea, where it has been consumed as white tuna, there was a move to amend the law to prohibit its consumption, but it has continued to be distributed disguised as tuna since then. In China, some companies offer this species disguised as salmon and cod. In Taiwan, on the other hand, there are no restrictions on distribution, and the fish is eaten as sashimi. Of course, in the U.S. and other countries, it is sold in supermarkets and is therefore an edible fish.

In other words, the only problem is that cheap fish is disguised as tuna to sell it at a higher price.

The post What is white tuna? first appeared on Sushiblog－Sushiuniversity.

The tastiest and most highly utilized Katsuo are Ma-gatsuo and Hon-gatsuo.Anyone can tell a fish is a different species if it looks different. However, there are cases where the appearance is so similar that you can’t just inadvertently make a mistake. That is when there are several species and the difference in value is significant. In the past, the fish was used as a fish fraud, and even today it is often used as a substitute.

So, the marketer adds the prefix Hon (本) in the name of a fish or shellfish to avoid confusion with a substitute. One of the meanings of the Japanese word “hon” is “genuine,” so this may have something to do with it.

For example, Hon-zuwaigani refers to Zuwaigani, which has a shorter fishing season and a much higher price than Beni-zuwaigani. To avoid confusion with Beni-zuwaigani, which has a similar name, the Hon is added to emphasize the fact that it is Zuwaigani.

Other fish names begin with the letter Hon.

・Hon-mirugai is Mirugai clam (Mirugai). To avoid confusion with Shiro-mirugai, which was considered a substitute for Mirugai in the past, Hon is added to emphasize the fact that it is Mirugai. Recently, however, the catch of Shiro-mirugai has been decreasing, and the price of Mirugai has skyrocketed.

・There are five main types of tuna distributed in Japan, including Minamimaguro, Mebachi, Kihada, and Binnaga, of which Kuro (kuro means black)-maguro, the largest, is considered the finest. As the name suggests, half of the fish’s body is black from the back to the lateral line, so it is so-called.

About 2 million tons of tuna are caught annually worldwide, but Kuro-maguro is only about 1% of that amount. Originally, maguro meant Kuro-maguro, but other species (Mebachi, Kihada, etc.) are now distributed, and to distinguish them from Kuro-maguro, what was originally called maguro is now called Hon-maguro.

・Aka-kamasu, also called Hon-kamasu, is considered the most delicious of the kamasu family and is sold at high prices in the market. On the other hand, Yamato-kamasu, also called Mizu-kamasu, is a little less tasty, and the name seems to be used to distinguish Yamato-kamasu from Aka-kamasu.

・The official name of the family Pandalidae called Amaebi is Hokkoku-akaebi. It is widely found from the coast of Hokkaido to Toyama Bay and the eastern coast of the Korean Peninsula. It is widely found from the coast of Hokkaido to Toyama Bay and the eastern coast of the Korean Peninsula.

・Akagai is simply called Tama, Hon-dama, Hon-aka, etc. in the Toyosu market. There is also a Bachi-akagai that is very similar to the Akagai, but its real name is Satogai, which is not as red as Akagai and is smaller in size. Satogai is often mixed in with hon-dama and are called Bachi-akagai from Bachigai (it means out of place).

Finally, some seafood uses both Hon and Ma.

For example, there are four species of bonito: Katsuo, Suma-gatsuo, Marusouda-gatsuo, and Hirasouda-gatsuo. The tastiest and most highly utilized Katsuo are Ma-gatsuo (katsuo) and Hon-gatsuo (katsuo).

For your reference.

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Fish names include scientific names, standard Japanese names, local names, and foreign names.

Scientific names are the scientific names of organisms. They are written in Latin for international uniformity. They are also listed in fish-illustrated books. Standard Japanese names are defined by the Ichthyological Society of Japan. Local names are various names given to one species in different regions. In addition, when looking at English and French names, they do not correspond to species as in the Japanese standard Japanese name, and it is not uncommon for different species to have the same English name, or for multiple species to be called by the same English name. It is rare in the world that each fish species has its standard Japanese name, as is the case in Japan.

In addition to standard Japanese names and regional names, fish names unique to the Japanese language are sometimes used. For example, you have probably heard of the fish named Aji (鯵). Then is Ma-aji (真鯵) a different fish?

Actually, they are the same fish. The “Ma” in the name of a fish or shellfish indicates that it is the most representative, the most superior, or the most valuable among the many related species. The Chinese character “真” means “genuine.

For example, a total of 146 species of horse mackerels have been identified, including Japanese scad (Maru-aji), Bigeye scad (Me-aji), White trevally (Shima-aji), Amberstripe scad (Muro-aji), Red Scad (Aka-aji), Roughear scad (Oakamuro-aji), Great trevally (Gingame-aji), and Torpedo scad (Oni-aji). Ma-aji is the most commonly caught and represented species of Japanese Aji species.

There are other fish names beginning with Ma, which are briefly introduced below.

・Ma-iwashi (真鰯) is a representative of sardines (Katakuchi-iwashi, Urume-iwashi, etc.).

・Kaki refers to Ma-gaki (真牡蠣). Ma-gaki is in season during the cold season and is mostly farm-raised, but there is a type of Kaki that is in season during the summer. It is called Iwa-gaki (岩牡蠣) and is characterized by its larger shells and meat compared to Ma-gaki.

・Anago with high market value are Ma-anago (真穴子), Goten-anago (御殿穴子), and Kuro-anago (黒穴子), but it is safe to assume that most Anago used in sushi restaurants are Ma-anago.

Other Ma (真) include Ma-dai (真鯛), Ma-dako (真蛸), Ma-dara (真鱈), and Ma-hata (真羽太).

Reference.

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What is hybrid fish?

Both Yamame (Landlocked Sakuramasu) and Japanese Iwana (Char) are members of the salmon family. Iwana and Yamame both inhabit the upper reaches of rivers, although Iwana prefers slightly cooler water. In rivers where each species lives alone, both fish occupy the upper reaches of the river, but in rivers where both species live, they do not mix, with Iwana occupying the uppermost reaches and Yamame occupying the lower reaches after a certain point in the upper reaches.

In nature, different species sometimes interbreed and produce hybrid fish. For example, hybrids between Yamame and Iwana are common in nature. The characteristic spots of the Iwana look like those of the Saba (Mackerel), a marine fish, and hence the name Kawasaba. They also rarely become smoltified (silvering) and become the descending sea type, but they do not reach sexual maturity.

Incidentally, the Kawasaba is thought to have been created by the uncontrolled release of Yamame into an area originally inhabited by Iwana, resulting in the mating of two species whose habitats do not originally overlap. The “hybrids” created by thoughtless releases may be a symbol of the destruction of genetic diversity.

What is hybrid artificial fish?

In the aquaculture industry, high growth and survival rates, good flesh quality, and disease resistance are important requirements for a superior species, and artificial crossbreeding has long been used as a method to create such breeds.

In 1964, Kinki University in Japan succeeded in breeding the first hybrid artificial fish, a female Red seabream (Madai) with a male Blackhead seabream (Kurodai). Since then, he has produced many hybrid combinations. The name “Ma-kurodai” is a combination of “Madai” and “Kurodai. In addition, he has created nearly 20 new fish species, including Madai x Hedai (Ma-hedai), Madai x Chidai (Ma-chidai), Ishidai x Ishigakidai (Kin-dai), and Buri x Hiramasa (Buri-hira).

Typical hybrid artificial fish will be mentioned briefly.

What is Buri-hira?

Buri hira is a crossbreed between a female Japanese amberjack (Buri) and a male Goldstriped amberjack (Hiramasa). Buri, which is in season in winter, is characterized by its high fat content and strong flavor, but its meat is tender and its dark red meat (chiai) tends to discolor during the summer. Hiramasa, on the other hand, is firm, has less dark red meat (chiai), and is less prone to discoloration, but has less fat and a lighter flavor, and is only available in summer.

Buri-hira is a very tasty fish that combines the “good points” of these two fish species and combines the “umami” of Buri with the ” chewiness and beauty” of Hiramasa. Because it is completely farm-raised, it can be served all year round, and major conveyor-belt sushi chains have already begun serving Buri-hira. Buri-hira can be caught in the wild very rarely, but they are so few that they are not generally available on the market.

What is Kue-tama?

It is a hybrid species, having as its father a Giant grouper (Tamakai), one of the world’s largest members of the grouper family that can grow to 270 cm in length and 400 kg in weight, and as its mother a Longtooth grouper (Kue), which is a rare and high-end fish with an outstanding taste and popularity.

The hybrid is characterized by the fact that it inherits the growth rate of Tamakai and grows to shipping size in about two years, whereas it normally takes four to five years for farmed Kue to grow to shipping size.

This makes it possible to significantly reduce production costs, and it also has properties that make it resistant to disease and easy to grow. Major conveyor-belt sushi chains have already begun offering Kue-tama.

What is Be-ster?

Be-ster is a hybrid of Beluga and Sterlet, known for producing the finest caviar among sturgeon. Developed by Russia several decades ago for aquaculture, the Be-ster was created amid a worldwide ban on capturing wild sturgeon as an endangered species.

What is Kin-dai?

Kin-dai is a hybrid of a female Barred knifejaw (Ishidai) and a male Spotted knifejaw (Ishigakidai) and was first successfully produced by Kinki University in 1969, and patented and trademarked in 1975.

Ishigakidai, on the other hand, takes more than six years to mature and produces fewer eggs, but grows quickly to commercial size. Kin-dai combines the best features of both, with a good texture and excellent taste. Its name is the same as the abbreviation for Kinki University.

Ishidai is called “Kuchiguro (kuchi means mouth and guro means black)” because its body turns silvery white and the area around its mouth turns black. Ishigakidai, on the other hand, is called “Kuchisiro (shiro means white)” because they have a black body and the area around their mouth turns white. Kin-dai’s entire body turns black, and the tip of its mouth also turns black.

What is Ma-chidai?

Kinki University has also produced a hybrid Ma-chidai, a cross between Red seabream (Madai), which grows well, and Crimson seabream Chidai, which has a less faded red coloration, and has traits that give it a red coloration like natural fish and faster growth than Chidai.

Finally, a second generation has already been produced from the sexes of the hybrid fish. If the hybrid fish are released into natural waters, contamination will occur through genetic infiltration. We should not leave a bad legacy for future generations.

Finally, a shocking incident occurred involving Atlantic salmon, a hybrid artificial fish that has already been put into practical use.

On February 9, 2025, an incident occurred at the world’s largest salmon processing company, Mowi, located in Troms County, Norway, where 27,000 farmed salmon escaped. The company offered a reward of approximately $45 per fish for their capture.

Experts warn that the escaped farmed salmon pose a significant risk to wild salmon in the region. They could compete with wild salmon for spawning grounds, potentially spreading diseases like salmon lice. Additionally, there are concerns about the impact of hybridization, as escaped farmed salmon could interbreed with wild salmon and alter their genes.

The same incident has occurred in Japan. However, no capture operation has been implemented.

Fish that should not exist in the wild have been repeatedly sighted in Kagoshima Bay. According to experts, these are hybrid fish created by artificially crossbreeding the high-value fish kue and the tamakai, known as one of the world’s largest groupers. It is likely that they escaped from a farm, but details remain unclear. The possibility of natural reproduction cannot be ruled out, and experts are concerned about the impact on the ecosystem.

In summary, the possibility of hybrid fish reproducing in the wild cannot be completely ruled out. While it would be costly, safe land-based aquaculture is preferable for preserving the ecosystem.

The post What is hybrid artificial fish? first appeared on Sushiblog－Sushiuniversity.

The role of the pressure receptors in the mouth is to obtain information to determine if food can be digested and nourished. Digestion is made possible by physically destroying the food, making it smaller, and breaking it down with enzymes. Only when the molecules are small enough can they be absorbed by the small intestine and other organs. Chewing in the mouth is the first step in this process. In the process of chewing, the food becomes smaller and smaller, and the texture changes rapidly.

The Japanese are the ethnic group with the most textural language. According to a survey on the number of terms related to texture, Japanese has about 500 words related to texture. In contrast, Chinese has about 150 words, French about 250, and German and English about 100. The Japanese have created a wide variety of foods with different textures by distinguishing and enjoying the differences among these many words used to describe textures.

Texture and taste are not directly related, since they are sensed by different receptors and are carried as information to the brain by different nerves, but the release of taste substances from hard foods is slower, and thus taste is perceived more slowly. On the other hand, the opposite is true for soft food, which tastes more quickly.

Nigiri sushi is made with an emphasis on texture. The act of aging sushi topping is waiting for the texture to soften in terms of physical changes. The purpose of this is for the sushi topping to adhere to the sushi rice. In conjunction, it is waiting for the production of inosinic acid, an umami substance. Shrimp, squid, and other ingredients not only become softer but also change to a gooey state. In this way, there is an aspect that makes it easier to perceive the taste.

Several techniques are used to mix the sushi ingredients and sushi rice in the mouth. We make sure that one or the other does not move first from the mouth to the back of the throat. If the sushi rice remains in the mouth, it is equivalent to eating sashimi, and the synergistic effect of umami cannot be expected. The way to do this would be to slit the sushi topping as much as necessary. The sushi rice and the sushi topping become as if they are one food. Of course, this also serves to improve the texture by cutting off white streaks and small bones.

Even the same portion of the same sushi item can have different textures depending on the sensitivity of the sushi chef. In other words, the taste changes. It is as if one were to choose a 500-word term for the texture, and then cast a spell on the sushi item. It is fun to guess what the sushi chef wanted to express.

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Revision date: February 26, 2024

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We would like to examine this challenging title that appears regularly in the media.

This story has not recently come to a boil; in fact, it is already widely known. However, the reason it is a recurring topic is due to the fact that the assumptions between the writer and the reader do not match. The reason for this is that the writer tends to exaggerate a bit in order to get people to read the article. The readers, on the other hand, are overwhelmingly uninformed and are led to feel uneasy about what they hear. Here’s what we guess.

So, in order to explain this issue properly, we will squash any ambiguities.

There are three major risks.

The first is food poisoning due to bacterial growth. The second is food poisoning by parasites. The third is the medium- to long-term effects on the human body of mercury, dioxin, microplastics, and other substances that accumulate in tunas.

We can say that food poisoning caused by bacterial growth is a very rare and serious matter that can affect the survival of a business, if only in sushi restaurants. Here are some data to support this. According to data from the Tokyo Metropolitan Government, the percentage of food poisoning cases occurring at sushi restaurants is less than 0.8% of the total number of food poisoning cases. The data shows that food poisoning rarely occurs at sushi restaurants.

The reasons for this are largely related to soy sauce, salt, and vinegar. First, soy sauce has bacteriostatic properties, and by marinating tunas and other fish in soy sauce, the growth of bacteria is inhibited. Second, salt has a bactericidal effect, killing bacteria on the surface of the fish. Besides, it uses osmosis to expel the rotting components of fish meat, etc. And vinegar also has a sterilizing effect. Since the ㏗ is 2~4, the bacteria are almost killed when they come in contact with vinegar. Sushi chefs put vinegar on their hands or wipe their knives with a cloth dipped in vinegar to sterilize them. Shari is made with vinegar and salt, so it is also sterilized. In other words, more steps are taken to prevent the growth of bacteria than in any other dish.

Next, we will examine food poisoning caused by parasites; Anisakis accounts for 50% of all cases of food poisoning. It can be said that raw seafood always contains parasites, but removing these parasites is the foundation of a sushi restaurant, and Anisakis, which can be visually identified, cannot be overlooked. On July 2, 2021, a method to kill Anisakis with a high current was also announced and will soon be put to practical use.

Also, it totally depends on where you eat. Do you buy it at the supermarket or fish market and eat it at home or a sushi restaurant? Even at the same sushi restaurant, there is a difference. Is it a conveyor-belt sushi restaurant with a chain or an individual restaurant run by a master and his apprentice? In our opinion, however, food poisoning caused by Anisakis has not occurred in private restaurants.

We will examine the medium- and long-term effects of toxic chemicals. First, let’s look at the effects of mercury. For example, the level of effect is naturally different for those who consume tuna every day and those who eat tuna once a week. Although the Japanese eat a lot more tuna than other countries, the effects of mercury accumulated in tuna have not yet been widely discussed. The effects of mercury on the mother’s body are well known, and the following warning is given by the doctor in charge.

In Japan, if you eat more than 160 grams of tuna per week, you need to be careful. Pregnant women do not bother to eat 160 grams of tuna in the first place. In addition, although Kuromaguro (Bluefin tuna), Mebachi (Bigeye tuna), and Minamimaguro (Southern Bluefin tuna) have safe amounts, Kihada (Yellowfin tuna), Binnaga (Albacore), and Mejimaguro (Young bluefin tuna) do not require any restrictions on the amount eaten. Also, there is no need to worry about canned tuna. This is also a well-known story.

And, this may come as a shock to tuna lovers, but it is the toro part of the belly that tends to accumulate the most dioxin, which is considered the best part of the fish. The toro is mostly fat, and dioxin taken in from feed and seawater accumulates there. In nature, the toro portion of tuna is normally about 20% of the tuna meat. However, in fattened tunas, 70~80% of the body is toro. The meat of fattened tuna is a habitat for dioxin. According to some research data, the amount of dioxin accumulated in fattened Kuromaguro was about 2 to 3 times higher than that in wild tuna, and in fattened Minamimaguro, it was about 2 to 10 times higher.

The final section examines microplastics’ medium- and long-term effects on the human body.

In the North Pacific Ocean gyre, famous for the Pacific Garbage Belt, plastic fragments have been found in the digestive tracts of 10%-35% of the fish examined. Many researchers have noted that microplastics are vectors that bridge harmful pollutants to fish and marine life. U.S. health officials estimate that less than 0.3% of microplastics taken into the human body reach the body’s lymphatic and circulatory systems from the gut. And only a very small fraction of these microplastics affect the body’s organs. Still, the effects of microplastics taken into the body on human health are not fully understood.

In 2014, the Ministry of the Environment’s survey on the actual state of marine debris reported that the amount of microplastics in the waters surrounding Japan was 16 times more than in the North Pacific Ocean and 27 times more than in the world’s oceans. And yet, around 2020, major media outlets are only now beginning to report on the issue. Unfortunately, this is one of the topical issues that Japan is still turning a blind eye to. In fact, this is a more serious problem in the world, and we imagine it will be sensationalized soon. We should put some restrictions on countries and companies dumping plastics into the oceans. Japan must be proactive in this regard in order to achieve the SDGs.

In conclusion, we think this title comes from the media’s self-righteousness.

We are not a researcher and cannot say that it is absolutely safe. It is a medium- to long-term issue that should not be neglected with careful monitoring. But in general, Tuna is an expensive food, so it should be economically difficult to consume it in large quantities. Instead, the media should focus on rice, wheat, corn, and other foods that are consumed daily. For your information.

Related contents:

Worried about mercury in fish? California researchers find a possible fix

We hope this information will be helpful.

Revision date: May 2, 2025

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Sushi continues to spread throughout the world. Nowadays, not only sushi rolls but also Nigiri sushi can be eaten all over the world. But if you have the opportunity to come to Tokyo, we want you to go home with sushi toppings that you can only eat in Tokyo. Not seafood exported from your country, but sushi made from natural seafood caught in the seas around Japan.

First of all, what kind of sushi do you think of when you hear the word “Nigiri sushi”? Most people think of sushi with Hamachi or Salmon on top of vinegared rice.

This is correct if you only look at the appearance. However, from the essence of Nigiri sushi, it is clearly wrong. In order to make your understanding perfect, we dare to confuse you, but we would like to understand the term “Edomae sushi” as well.

What is Edomae sushi?

Nigiri sushi and Nigiri are words you may have heard before. However, “Edomae sushi” is a word you may not be familiar with, so it is important to understand exactly what it is.

It is quite simple.

Edomae sushi consists of Nigiri sushi and Nori maki. Nigiri sushi originated in Edo (now Tokyo) about 200 years ago, while Nori maki is said to have originated 50 years earlier. And Edomae sushi has remained almost in its original form to the present day. We will skip the explanation of Nori maki here, so you can just assume that “Edomae sushi” and “Nigiri sushi” refer to the same thing.

Now let’s dig deeper into the story of Nigiri sushi. You have probably seen Nigiri sushi and Nori maki before. If you do not like fish and nori, you have probably eaten them.

However, many people, including the Japanese, misunderstand Nigiri sushi.

They think that Nigiri sushi is sushi with sashimi such as salmon on top of vinegared rice. Many cookbooks and other books say this as well, so it is no wonder they understand it incorrectly.

To correct here, nigiri sushi consists of prepared fillets on a bed of vinegared rice. Preparation means sprinkling salt on the seafood, soaking it in vinegar or soy sauce, boiling it, simmering it, etc. This preparation is called Edomae shigoto (Edo-style preparation) in Edomae sushi restaurants. To confirm, sashimi is unheated seafood or other ingredients cut into small pieces.

Why do they dare to prepare super-fresh seafood?

The reason is said to be that in the Edo period, there was no such thing as a refrigerator, and people had to devise ways to keep seafood from spoiling even a little.　Then it seems that it is not necessary now. However, this preparation process helps to make seafood more delicious (to give an example, inosinic acid is produced, which, combined with the glutamic acid and other substances that seafood originally contains, produces a synergistic effect of umami). This is why they still use prepared seafood today.

On the other hand, salmon nigiri sushi found overseas uses sashimi. Even in Japan, in regions where fresh seafood is available, sashimi is used. This is because the priority is not the synergy of umami, but rather the texture and security of freshness. And there is no way to know that this is clearly different from Edomae sushi (Nigiri sushi) on the main road.

If you make nigiri sushi with sashimi, you don’t have to be a sushi chef to do it. In fact, to put it bluntly, anyone can do it. There is an experience to make Nigiri sushi for tourists, but you understood that this is only to make Nigiri sushi in appearance, right? And to learn Edomae shigoto (Edo-style preparation), the sushi chefs need a long period of training.

Let’s get to the point here.

Here are 8 sushi toppings you should try in Tokyo. We divided it into 4 so that you can see the opportunity to eat.

The first is the typical sushi toppings at Edomae sushi. It is a sushi topping that can be eaten regardless of the season (of course, there is a season), but it shows the characteristics of the sushi restaurant. The boiled Kuruma ebi, with its beautiful red color, aroma of the sea, and complex umami, is a must-try. Next is not eel but Anago (Japanese conger). The soft- simmered anago instantly falls apart in your mouth, spreading the ummai of the fish, and the restaurant’s unique sauce, called Nitsume, is not to be missed.

Second, sushi toppings are only available at certain times of the year. The season is short, so even if you want to eat it, you will have to wait until the next year when the season is over. For example, don’t you think you can eat Bluefin tuna all the time? The season for fresh bluefin is from around September to early January. This is the time when all parts of the fish are at their best. Shinko, the juvenile kohada, can cost as much as $2,000 per kilogram at the beginning of the season, and sushi chefs are forced to pay a premium for this fish because sushi lovers compete to be the first to eat it. The taste is not as good as kohada, but the aroma may be a cut above.

Chum salmon is not eaten raw in Japan. This is because of problems such as anisakis. Even so, you should definitely try Keiji (young Chum salmon) nigiri, which has a completely different quality of fat. It is very rare and costs more than US$1000 per fish. Then there is Hoshigarei, the king of flounder. The moderate fat and fresh aroma will fascinate you. Next, the Red sea urchin is caught in Kyushu and other parts of Japan. Sea urchin has a rather complex flavor. However, red sea urchin has a refreshing aftertaste. It is a mysterious sushi material.

The fourth is the sushi items that you should eat without grumbling. You should be happy to eat these items in season. Ezobafununi, caught in Hokkaido during the summer, is exceptional. Many people say they can’t eat sea urchin, but if you eat this, you’ll become a sea urchin lover. And then there is Akagai (Ark shell). Many shellfish enjoy the delicate balance of sweetness and bitterness, but Ark shell is a great ingredient to enjoy the scent of the sea.

If you want to eat Hamachi or Salmon, which you often eat as Nigiri sushi, you have to go to a conveyor belt sushi restaurant. Buri, which is farmed, is called Hamachi. Salmon is also mostly farmed, with Norway and Chile being the world’s leading producers. There is no point in going all the way to Tokyo to eat them.

Finally, sushi chefs tend to avoid farmed fish. And the same goes for frozen fish. Some fish can only be used for Nigiri sushi if they are live. The chef cooks fish deliciously, but sushi chef is only trying to bring out the true flavor of the fish. In other words, there is no compromise in the selection of seafood. If the fish is too expensive, sushi chefs may not buy it. And sometimes they have to buy it even if it is too expensive. For your information.

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Revision date: August 12, 2023

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As fish and meat age, their components change, losing their deliciousness while at the same time producing dangerous components that can be harmful to the body. Freshness is determined by the amount of time that has passed since the fish was caught. By knowing the freshness, we can tell how fresh the food is, and at the same time, we can tell if it tastes good and is safe.

To swim, fish consume adenosine triphosphate (hereafter referred to as ATP) in their muscles to generate kinetic energy. While the fish is alive, ATP is resynthesized through respiration and the breakdown of glycogen in the body, even if the muscles are fatigued.

However, if they die and are no longer supplied with new ATP, the binding of actin and myosin, the proteins that make muscles stretch and contract, proceeds unilaterally. In combination with the acidification caused by the breakdown of ATP and the formation of lactic acid, the muscles remain contracted. This is the onset of rigor mortis. Finally, ATP is lost and rigor mortis is completed. If a fish dies while its body is exhausted from strenuous exercise, rigor begins earlier than normal. This means that ATP is consumed when fish resist violently to avoid being caught.

K value is a scientific and objective standard for judging the freshness of fish and other products.

To begin with, the postmortem flesh of fish is said to be alkaline. It becomes more acidic over time. In the process of this change, ATP is broken down into several acids as shown below, and the K value is a mathematical formula that captures some of these acids and calculates them.

ATP→Adenosine diphosphate（ADP）→Adenosine monophosphate（AMP）→inosinic acid（IMP）→hypoxanthine riboside（HxR）→Hypoxanthine（Hx）

The formula is as follows:

K value (%) = (HxR+Hx)/(ATP+ADP+AMP+IMP+HxR+Hx)×100

The rate of degradation varies among fish species, but the pathway to HxR is constant. Fish that die quickly after catching have more ATP, ADP, and AMP. Then, as time passes, IMP increases and finally HxR and Hx increase. These HxR and Hx present a tasteless or bitter taste, which causes a decrease in deliciousness. In other words, a high amount of HxR and Hx is evidence of reduced freshness.

In general, fish with a K value of up to 20% can be eaten raw, i.e., as sashimi. In the case of fish, the K value is about 5% immediately after ikejime. 20-40% is considered to be good freshness. Sushi toppings are around 40%, which is not low by any means, but it is at this value that the flavor of the ingredients is most likely to be extracted. In other words, it is a state of maturing and increased IMP. And if it is 40-60%, it is edible if cooked. In other words, it is better to eat simmered or grilled fish. If it is over 60%, it is in a state of decomposition. Naturally, it is not suitable for eating. It is also known that the rate of increase in K value is large for cod and red-fleshed fish, while the rate of increase in K value is small for white-fleshed fish such as red sea bream and flatfish.

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Revision date: July 25, 2023

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The post What is K value, a formula to evaluate the freshness of fish? first appeared on Sushiblog－Sushiuniversity.

Tuna, which is now a representative of high-class fish, was one of the lower ranks of Gezakana (ge means ‘cheap’, and zakana means ‘fish’) in the Edo period. According to an encyclopedia of the Edo period, “maguro is a very vulgar fish, and even common people who live in houses facing the main street would be ashamed to eat it. Maguro was so low-ranked fish that was said to be the food of poor people living in houses on back streets. However, due to the effects of global warming and overfishing, the number of fish called Gezakana has been decreasing. Therefore, meat is definitely cheaper than fish in supermarkets.

Next, please take a look at the ratings of fish in the Edo period as listed in Chiba University‘s study of classical cuisine.

The following fish are listed as Jyozakana (Top-grade fish)

Tai、Ankou、Amadai、Sayori、Shirauo、Suzuki、Sawara、Ishigarei、Ayu、Tara、Akagai、Kaki、Karei、Kisu、Kurumaebi

The following fish are listed as Chuzakana (Middle Fish)

Tako、Kochi、Hirame、Aji、Ara、Ika、Katsuo、Houbuo、Ishimochi、Ungai、Ainame、Asari、Hamaguri、Bora

The following fish are listed as Gezakana (Lower fish)

Buri、Kurodai、Saba、Iwashi、Fugu、Kohada、Mutsu、Okoze、Shimaaji、Maguro、Nishin、Same

Again, maguro is classified as Gezakana, along with today’s high-end fish such as Kurodai and Fugu, and it seems that most Jyozakana are white fish, and the oily fish, so much appreciated today, was not favored by the people of Edo. In addition, maguro was also called shibi (pronounced “shi,” which is a reference to death), and some believe that it was not popular because it was associated with death.

When large schools of maguro appeared in the seas around Edo (Tokyo) between 1340 and 1844 and were caught in large numbers, they were sold for free because they were not popular.

As a side note, a sushi restaurant made a fortune by purchasing maguro red meat at a low price, marinating it in soy sauce, and selling. This was the beginning of what is now called Zuke.

n this way, red meat was still sometimes preferred, but Toro, which tends to spoil easily, was not looked upon and was often thrown away. Even if it was eaten, it was only in Negima nabe (hot pot) and was rarely eaten raw.

It was not only in the Edo period that toro was not favored.

It was not until the development of refrigeration and freezing technology in the 1945s that otoro and chutoro became as much appreciated as they are today. It is only recently that Otoro and Chutoro have become the kings of fish. Fish grading, in fact, has a great deal to do with safety. Saba, which suddenly loses its freshness, and Iwashi, which is tender and easily loses its freshness, are both Gezakana. In other words, fish that lose their freshness easily were likely to be classified as gezakana.

Another reason was the taste of the Edo people, who preferred light fish such as Amadai, Sayori, and Suzuki to oily fish such as Saba and Buri. It is understandable that Maguro Toro, which is both fatty and perishable, is frowned upon.

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Revision date: July 24, 2023

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In Eastern Japan (such as the Kanto area), Inarizushi is often shaped like a bale or rectangular pouch and features a strong sweet and salty flavor profile. In Western Japan, particularly the Kansai region, it tends to be triangular and lighter in flavor, with a noticeable emphasis on the umami of dashi (soup stock). These regional styles reflect not only taste preferences but also local food culture and beliefs.

Type of Inarizushi

When categorized based on shape, the types of Inarizushi are bale type, triangle type, open type and roll type. They can also be categorized by the type of rice stuffed into the fried tofu (abura-age): either white vinegared rice or vinegared rice mixed with other ingredients. The four elements that make up the flavor are sweetness, soy sauce, soup stock and acidity, and the balance is very important. In the east of Japan the flavor tends to be a stronger sweet and salty while in the west the soup stock is more apparent.

Here we will explain the characteristics of Inarizushi using categories based on appearance.

Bale Type

Inarizushi seems to be a version of Sugatazushi. Perhaps the Sumeshi is stuffed into the fried tofu instead of into a fish (a hypothesis). When looking at literature from the Edo period, there is Inarizushi in the form of a long rod that was cut up and sold. Someone probably thought that if they were going to cut it up into bite-size pieces anyway, they may as well make it in easy-to-eat sizes in the first place (an inference). There are some shops that still sell Inarizushi in long rod form, but the difference is probably in how the fried tofu is cut. You can find this from Sekigahara, Gifu and further eastward.

Triangle Type

Why is the appearance triangular? There are many theories, but the most plausible is that these are meant to be shaped like a fox ear. Inarizushi originated as an offering to the Inari god at festivals. The Inari god is the deity of agriculture and patrons pray to this god at Inari shrines. The head Inari shrine is Fushimi Inari Taisha in Kyoto. Legend has it that fried tofu is a favorite of foxes, who are said to be messengers of the Inari god, so it was made into the shape of fox ears. Another theory is that it is the shape of Mt. Inari where Fushimi Inari Taisha is located. Apparently this is because the triangle type originated at Fushimi Inari Taisha. However, Inarizushi shops in Kansai use lucky bale shapes in order to pray for prosperity in business. On the other hand, Inarizushi made at home or in soba restaurants are usually triangular. This type is found from Sekigahara, Gifu and westward.

Open Type

The open type is a revolutionary style. How it came about is not clear, but perhaps someone just stuffed it too full of ingredients. Since the ingredients are visible, it looks even more delicious than normal Inarizushi. It’s really beautiful when many are lined up. You can imagine how this served as inspiration to those who went on to add a variety of ingredients. It’s also easy to make since all you have to do is fill it with ingredients. It is now widely recognized for its aesthetic appeal and versatility. Open Inarizushi has spread internationally and has become a beloved style in countries such as France, South Korea, Australia, and Singapore.

Roll Type

Almost all roll-type Inarizushi in Japan is made with a dried fried tofu from Kumamoto called Nankanage. Unlike normal fried tofu, it looks like paper in the shape of a sponge and does not form a bag. That’s why the only way to use it was by wrapping it around the rice. Also, this method might have emerged as a practical solution to avoid tearing the tofu while stuffing it.

Summary

Ignoring whether or not it is true that carnivorous foxes really love fried tofu, apparently the foxes that serve as messengers to the Inari god do love it. As foxes were thought to be delivering prayers to the Inari god, their favorite fried tofu was given as an offering to stay on the fox’s good side. After that, they started the practice of stuffing rice that was grown with the blessing of the Inari god. As you can see, Inarizushi is the combination of two ingredients involving the Inari god.

Related contents:

Tips for making great Inarizushi from a sushi chef

TYPES OF SUSHI

We hope this information will be helpful.

Revision date: July 9, 2025

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The post What is Inarizushi (Inari sushi)? first appeared on Sushiblog－Sushiuniversity.