Basic Knowledge | Sushiblog－Sushiuniversity

What is Ichthyohemotoxin?

a photo of anago blood — Fillet Anago and then make nigiri sushi.

Among the fish that belong to the Anguilliformes order such as Eel, Conger eel, and Moray eel, some contain toxic components in their blood serum. This type of serotoxin is called Ichthyohemotoxin and indicates lethal and hemolytic actions. However, this is not the official name of the toxin, and the chemical structure is also not clear.

If a human were to drink a large amount of fresh blood from these fish, they would suffer from symptoms such as diarrhea, constipation, vomiting, cyanosis, arrhythmia, paresthesia, paralysis and respiratory distress, and it would then sometimes result in death. If the blood gets in your eyes, it causes an intense burning sensation, swollen eyelids, and a foreign body sensation that last for days. Sufficient caution must be practiced when preparing these fish, but there is no concern for toxicity if it is cooked. Incidentally, in case of Ichthyohemotoxin, found in eel’s blood, the toxicity completely disappears when cooked for 5 minutes at 60℃, so there are no issues with eating eel Kabayakai.

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Revision date: November 15, 2022

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What are Konacha and Mecha?

When it comes to green tea, I’m sure you’ve heard of Gyokuro (玉露) and Matcha (抹茶), but you are likely not familiar with Konacha (粉茶) and Mecha (芽茶). Let’s remedy that by explaining both Konacha and Mecha here.

First and foremost, the three broad tea categories based on the processing method of the young leaves include green tea, oolong tea and black tea, but these are all made of leaves picked from the same trees, and then end up as completely different teas just by changing the processing method. Oolong tea and black tea are made by artificially fermenting the tea leaves as part of the processing. On the other hand, green tea is made without fermentation. The raw material of green tea that is eventually made into Sencha, Gyokuro and Tencha (碾茶), which is the raw material for Matcha among others. Then Konacha, Mecha, etc. are byproducts of the process for making Sencha and Gyokuro.

First of all, Sencha is the foundation of Japanese tea.

Sencha is known for its gentle flavor with a lingering, but subtle sweetness amidst the inherent fresh scent and bitterness. Generally, the color of Sencha is a transparent yellowish gold. Freshly picked tea leaves are immediately steamed, stopping the fermentation process. The steaming process gives each completed, individual tea leaf a deep green color. Tea was originally introduced to the world from China, but Sencha is the only tea with a unique, deep flavor created by Japan. About 80% of the tea produced in Japan is said to be Sencha. The most delicious Sencha comes around from the end of April to May, which is the beginning of the tea season. The appropriate volume of tea when steeping for one person is 2 to 3 grams of tea leaves to 70 milliliters of hot water and the appropriate water temperature is around 70℃ in order to bring out the sweetness and umami.

Next, we’ll describe Gyokuro.

By blocking sunlight and growing in the shade during the sprout timing, the leaves for Gyokuro grow full of theanine, which is an umami component, ending up with tea leaves that have a unique sweetness. It is common to focus only on taste, but the fragrance, described as “enveloping” is also wonderful and should not be discounted. This fragrance is often described by people from outside of Japan as a having a seawater-like scent or being salty. Yame in Fukuoka, Uji in Kyoto and Okabe in Shizuoka prefecture are the three famous production spots for Gyokuro. The appropriate volume of tea when steeping for one person is 2 to 3 grams of tea leaves to 20 to 30 milliliters of hot water and the appropriate water temperature is around 50 to 60℃ in order to bring out the sweetness and umami. This will give you the ultimate cuppa that is the epitome of luxury.

Most of the Agari (cup of tea to finish the meal) served at sushi restaurants is Konacha.

By avoiding the use of a teapot and only preparing the number of teacups needed, directly in the cup, strong tea can be made just by adding the hot water later. Conventionally, steaming is a very important step in making tea, but it isn’t necessary with Konacha. Konacha raw ingredients are mainly made up of the broken tea leaves from the Gyokuro and Sencha manufacturing process.

Brewing konacha results in a dark, deep green color. As the name suggests, it has a lot of powder in it, so the tea leaves in powder form settle in the bottom of the teacup. There for it also carries the benefit of being richer in nutrients than other teas. The sense of transparency is moderate and has a bit of a more somber color. The appropriate amount of water when brewing konacha is one gram of tea leaves to 40 to 60 milliliters of hot water. Konacha is strong, so making it with water that is about 80℃ gives it a mellow flavor. Tea that is made quickly with hotter water gets a moderate bitterness typical of Japanese tea and cleanses the palate.

Also, Japanese people have treasured food since long ago. For example, the leaves of vegetables like daikon radish are sauteed and consumed rather than discarded. As a society they have spent many centuries making efforts to figure out how each part can be made delicious. Mecha is made by collecting the cut-off tips of sprouts and leaves in the process of manufacturing Gyokuro and Sencha. There are many people who think Mecha is tea made just from picking the small buds from tea trees, so don’t make that mistake.

Mecha is a strong green tea that gets a strong scent when brewed. The longer the extraction time is, the stronger the tea, so if the color is too dark it changes the impression it gives and also affects the flavor. That’s why it’s important to pay close attention to extraction time. In general, the volume should be 2 grams for 70 milliliters of hot water–the same as Sencha. When preparing for more people, fewer tea leaves should be used. When brewing, wait patiently for the rounded Mecha leaves to open up. Around 80℃ is the appropriate temperature, but if less bitterness is preferred then it can be made with hot water at 90℃.

In summary, Konacha and Mecha, which are teas used at sushi restaurants, are made from the broken-off parts of the tea leaves carefully selected for Sencha and Gyokuro. They don’t require the steaming step of the tea-making process, so they can be prepared quickly and include the appropriate amount of bitterness for cleansing the palette, making them perfect pairings for nigiri sushi.

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What is Ikekoshi?

When a fish is pulled from the sea, it is put into an extraneous environment with sunlight, temperature and hot human hands that it isn’t used to, so it starts to swim violently with all its might, trying to get away, in a perpetual state of tension. If cooked in this state, blood will still be running through all the cells of the body. There is no sense of transparency in the meat at this point, especially the white meat. The body also hardens. The entire body reeks of blood. In other words, the meat of white fish is full of blood, making it unsuitable for preparing as food.

Fish are placed in a tank with enough water and oxygen, only in numbers so that they do not rub up against each other. A lid is placed on the tank to create a temporary dark space. At this time, the temperature of the water is an ideal, low temperature. This keeps the fish from struggling. After being left for half a day, it will regurgitate anything undigested that was eaten prior to being caught, become acclimated to the dark space and settle down. The bloody tone from struggling fades throughout the body and the fish relaxes.

Creating this state is called “Ikekoshi”.

Ikekoshi methods differ depending on the species of fish, but the idea is to keep this state for only one day at most. When left for two or three days, the fish loses meat, starts to swim around the dark chamber that it has now grown accustomed to, and its body, tail and fins rub up against other fish or the sides of the tank, causing damage. This hurts the meat quality and appearance so it is something the fisherman must look out for.

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Revision date: August 5, 2022

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Do you know why canned crab is wrapped in paper inside the can?

Crab protein has a high sulfur content. This sulfur can bind with the iron in the can, resulting in ferric sulfide that causes black spots in the meat. Black discoloration of the crab meat significantly mars the appearance and reduces the product value. In order to prevent this, parchment paper with superior water resistance and oil resistance is used to keep the crab meat from coming in contact with the can.

Meanwhile, the trace amounts of magnesium, ammonium and phosphoric acid contained in crab and fish meat sometimes bind to create magnesium ammonium phosphate glassy crystals. This chemical phenomenon is called struvite.

These crystals have no taste or odor and dissolve easily in the stomach so they are not considered to be an issue under the Food Sanitation Act. However, large crystals may hurt the oral cavity so efforts are made to improve production methods to prevent generation of crystals and keep any crystals that do form as small as possible. However, parchment paper does not reduce the struvite phenomenon.

In summary, do you now understand the truth of why crab meat is wrapped in white paper? Of course, nowadays the surfaces of cans are processed in a way that the iron doesn’t start to dissolve, so perhaps the correct theory is that the parchment continues to be used to give a sense of luxury.

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Revision date: August 1 2022

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What makes good quality Kuromaguro?

There are three elements that make good quality Kuromaguro（Bluefin tuna）.

They are decidedly, color, fragrance and texture.

First of all, color does not simply refer to the color of the cross-section when the fish is cut with a butcher knife.

It refers to how long the fish maintains its “characteristic coloring”. After all, tuna darkens as time passes, eventually turning a burnt-brown color. The true, visual charm of Kuromaguro is the eye-awakening red color that catches your attention when the sushi is placed on a counter or plate. This wonderful coloring is a characteristic of tuna caught through longline fishing or single‐hook fishing. On the other hand, it is said that those caught in round haul nets don’t hold their color and don’t last long. When frozen tuna is thawed, it turns brown within a day. This focus on color is based more on Japanese restaurants that serve sashimi at tables that are located farther away from where the food is being prepared, than on sushi. Incidentally, Mebachi, despite also being tuna, holds its color longer than Kuromaguro does and is suitable for take-out sushi. Minamimaguro is a darker red color than Kuromaguro, but it also loses its color quicker. Kihada maintains its color best.

Next, where does Kuromaguro’s appealing fragrance come from?

The truth is that the source of fish flavor components is still being researched and there are a lot of unknowns. What we do know is that this fragrance is made up of many volatile compounds, but since there are only trace amounts of each one, they are difficult to analyze.

Yet, in the case of expensive Kuromaguro, every measure possible is taken to make sure this fragrance is maintained. Kuromaguro is a migratory fish that gets around by swimming at high speeds in the surface layer of the sea. It needs strong muscles to swim this fast. it also needs to circulate blood throughout its entire body in order to vigorously move those muscles. When a tuna violently struggles to resist and twists its body to avoid being caught, the proteins in its muscles (myosin and myoglobin) rapidly react with oxygen and start to degenerate. This causes Yake and the oxidized odor of tuna. It is important to catch the tuna while causing it as little stress as possible, quickly remove the organs and then use ice to rapidly cool the entire body. If this process is delayed then the pleasant fragrance will transform into an odor. In other words, the scent of Kuromaguro all depends on how it is processed after being caught.

The meat of Kuromaguro that is properly processed emits a unique aroma with a slightly acidic taste when you put it in your mouth. That fragrance lingers for a long time and it combines beautifully with the acetic acid of the sushi rice to go straight to your nose. Then, the moment the fish has disappeared down your throat, the scent of the iron and a subtle acidic taste linger very nicely. This experience is only possible with the exceptional Kuromaguro.

As for the texture, this is determined by the fat distribution of the tuna.

Especially in winter, the Harakami cross-section of Kuromaguro is marbled, much like the Ribulose of Wagyu beef. The melting point for the fat of high-quality tuna is low, and it starts to dissolve even at human skin temperature. This is why sushi chefs who are particular about the sense of unity between shari (sushi rice) and tuna, say, “Shari should be skin temperature.”

There are many chefs who say that the umami of Kuromaguro is in the fat. In the first place, Kuromaguro is one of the fattier fish, and especially between autumn and winter, the Kuromaguro that fed on Surumeika and Sanma has exceptional Harakami. The organs of both Surumeika and Sanma are rich, full-bodied and delicious, even when grilled and eaten by humans. In other words, it is the Surumeika and Sanma that the tuna feeds on that determine the quality of meat. As an example of the meat quality of tuna being affected by what that tuna fed on, Kuromaguro in the Atlantic ocean that has fed on Nishin may exhibit the scent of Nishin when made into sashimi.

However, having a high fat content is not the most important factor. For example, farmed Kuromaguro is fed a high-protein diet so that it will be fatty regardless of the season. Yet, the fat is tougher than that of the wild fish and it’s not something that leaves you wanting a lot more. In comparison, the fat of wild Kuromaguro has a fine texture throughout, immediately melts in your mouth and is digested easily. As sushi chefs know, the fresh fish seems to suction to their hands when making the nigiri sushi. In the same way, it has a smoothness that seems to suction to your tongue when you put it in your mouth. Once you’ve swallowed, it leaves you craving more.

This is the depth of wild Kuromaguro.

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Revision date: July 2 2022

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What is Odori?

Both conveyor belt sushi and premium sushi have versions of sushi made with raw sweet shrimp or botan shrimp. However, in Edomae Sushi, boiled shrimp is always used. The use of raw shrimp in sushi started in the Kansai region. Moreover, in the Kansai region, there are many restaurants that make sushi with live Kurumaebi known as “Odori or Kassha”. However, this way of eating may be declining nationwide. It is probably because there is increased texture when boiled, so it tastes better.

Going back to Odori, “Odori” means “dance” in Japanese and it is said that this name came from the fact that shrimp twitches on the sushi rice and looks like it is dancing. If you look up the roots, it seems that this method of serving started at a sushi restaurant in Kyoto City in the early Showa period. It spread throughout the Kansai region, but although Odori may look easy to make, the method is actually quite elaborate.

Let’s introduce the common recipe here. First wash the live Kurumaebi with fresh water and start by bending the head with your hand while detaching it from the body, then peel off the shell. Next, peel the skin off the abdomen and cut the abdomen open vertically. Fresh shrimp is difficult to peel, so it is important to do it very carefully. Next remove the veins from the back and sprinkle on just a bit of mirin and vinegar, then lightly rinse off with ice water. After that, parboil just the tail in boiling, salted water to make it look attractive.

Then make the sushi with the open side facing up. The direction is important because it is easier to tell that the shrimp is dancing when it is arranged this way. To finish, sprinkle lemon juice over the shrimp meat. This stimulates movement of the body.

Now let’s discuss how a customer eats Odori. It goes without saying that since the shrimp is still alive, the moment you dip the topping in the soy sauce, the shrimp twitches in its death throes, convulsing violently. Apparently the customers are greatly pleased to see this. We don’t recommend the faint of heart to order this dish.

Incidentally, eating only the shrimp in this way is called “Odorigui”. In China there is a dish in which living shrimp is soaked in Shaoxing rice wine or fermented alcohol, made drunk, and then eaten once it has settled down. These sorts of methods may be considered cruel in some western countries.

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Revision date: June 6, 2022

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What is Ciguatera fish poisoning?

Ciguatera fish poisoning is a type of food poisoning caused by consuming certain fish that live in tropical and subtropical coral reef areas such as Moray eel, Grouper, Star snapper, Japanese scavenger and Parrot fish.

It is caused by toxins such as ciguatoxin, but it mainly generates from dinophyceae that are stuck to algae. The process of ciguatera occurring involves the food chain. Even if a fish itself doesn’t originally contain toxins, an herbivorous fish may eat algae that turns it toxic. That fish may be eaten by a carnivorous fish, which then accumulates high concentrations of ciguatera in its body. When a human consumes the carnivorous fish it can cause food poisoning in the human. There are as many as 300 species of fish that contain ciguatoxin. The ciguatoxin, which causes the food poisoning, cannot be killed by boiling or grilling, so it can’t be prevented through food preparation.

Symptoms of this food poisoning mainly consist of sensory nerve abnormalities, muscle soreness, itchiness and abdominal pain, but it is rarely fatal. However, it takes quite a long time to recover from compared to other toxins and the average recovery time is said to be two to three weeks. It is vital to diagnose ciguatera fish poisoning as soon as possible. Most symptoms develop within one or two hours and up to to 24 hours after consumption and one unique symptom is dysthermesthesia. This is a form of dysesthesia in which touching cold things feels like its burning. It occurs one to two days after the poisoning and is a known characteristic of ciguatera fish poisoning. Another characteristic symptom of ciguaterafish fish poisoning is joint pain within 24 hours after consuming the fish. In any case, it is important to be seen by a specialist as soon as possible.

Incidentally, the name ciguatera came from Spanish immigrants to Cuba as a name for food poisoning caused by the cigua shellfish in that region. Later it was also used to describe fish poisoning, which causes similar symptoms.

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Revision date: May 9, 2022

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What is Yake or Yake-maguro?

Tuna fishing methods include Purse seine fishing, Fixed-net fishing, Drift-net fishing and Longline fishing, among others. Ocean fishing for tuna in the South Pacific Ocean, Indian Ocean and Atlantic Ocean, is often done by longline fishing. A main line can exceed 150 km in length and have over 3,000 hooks hanging from it. A main line is let out for 6 to 7 hours, and it takes 3 to 4 hours from running the line in the sea, to catching tuna. After that it takes another 10 to 15 hours to reel it up, so the tuna that was caught early may have already died during this time. There are times when sea water may feel warm to the touch, even in the dead of winter. The problem here is, that the body of the tuna that died early, will be warmer if the sea water is warmer. The body temperature will also be unusually high if a tuna caught by a hook ends up struggles for a long time and dying before being reeled in. The same is true for Kuromaguro caught in game fishing.

When this tuna is cut into pieces, the meat is whitish, as if grilled in a fire, so it is called “Yake (焼け)” or “Yake-maguro (焼け鮪)” as “Yake” means “burnt” in this case. The meat can also be a grayish-brown. In the industry it’s known as “White tuna” due to its color. It loses its characteristic red color, the texture of the meat when eating it is flakey and it doesn’t taste good.

Even if the fish body is cooled with ice water after catching, once the meat has been “burnt”, it won’t turn back to red. This renders even the premium Pacific bluefin tuna and southern bluefin tuna worthless, with zero commercial value as food. However, the fishermen don’t just toss the dead fish back into the sea without a second thought. This is mostly processed into pet food. Also, since it can’t be determined externally whether the meat is “burnt” or not, no one can tell until the fish has been cut open. It runs a big risk to the broker and can be a cause of its fishing port brand losing credibility.

It is currently believed that burnt tuna occurs from high temperature and low pH in the muscles of the fish after death, and that there is a complicated, indirect causal relationship between the conditions such as the environmental temperature, fishing method, handling of the catch, length of processing time, type of fish and size of fish. However, the mechanism that causes this phenomenon is not clearly understood.

A lesson on how the price of Nigiri sushi is determined

In order to prosper, a business wants to sell products at as high a price as possible. So how does a chef determine the price of nigiri sushi?

Naturally, the cost price is what it costs the restaurant for the ingredients while the price on the menu is the selling price. The ratio of these two prices is called the cost rate. In the case of a sushi restaurant, the ideal cost rate is 35% or less. A restaurant operating with only Omakase will have a cost rate of 40% with a focus on the quality of the toppings.

For sushi restaurants, handling of this ratio and the yield are very important. Yield refers to the part of the purchased fish and shellfish that can actually be used. For example, when purchasing a whole fish there are bones, skin, eyes, tail and internal organs that cannot be served as sushi or sashimi. No matter how good a chef is when preparing fish, the bones and skin will remain. In other words, the yield rate is the percentage of parts that can be used as sushi or sashimi. Typical fish yield rates are as follows:

Wild Maguro (Tuna): 65~75%

Buri (Japanese amberjack): 50%

Hirame (Bastard halibut): 40%

Tai (Red seabream): 35%

Akagai (Ark shell): 25%

Mirugai (Keen’s gaper): 20%

The weight of just the topping for a single piece of nigiri sushi is 12 to 18 grams, depending on the ingredients and the policy of the restaurant. The market price for rice is said to be about US$5 per kilogram, and assuming a weight of 15 grams per Nigiri, the rice for a piece of sushi is generally said to cost about US$0.05, including vinegar and salt. Even if you count the shari (sushi rice), soy sauce, wasabi, nori, etc., it’s fair to consider the cost to be about US$0.10.

Now, let’s figure out the price of Hirame, for which 3 kilograms were bought at $60 per kilogram. Assume that the weight of one topping is 15 grams.

The yield rate of Hirame is 40%, so the chef can make 1,200 grams of sushi toppings from 3,000 grams of Hirame. (formula: 3000 g × 0.4 = 1200 g). Since the weight of one topping is 15 grams, 80 pieces of sushi can be made from 3,000 grams of Hirame (1200 g ÷ 15 g = 80 pieces).

Next, we calculate the cost of one topping. Hirame is US$60 per kilogram, so US$180 (US$60×3 = US$180) for 3 kilogram. Since this volume can yield 80 pieces, the cost of one topping is US$2.25 (US$180÷ 80 pieces = US$2.25).

Add the shari price of US$0.10 to this: US$2.25+0.1=US$2.35. In other words, the cost of one Hirame nigiri sushi is US$2.35.

If the ideal cost ratio of 35% is applied here we get 2.35÷0.35 (35%) = US$6.71. For a restaurant serving mainly Omakase, 2.35÷0.4 = US$5.88.

In summary, one piece of Hirame sushi is sold between $5.88 and $6.71.

It may feel surprisingly cheap, but if you perform these calculations with Kuromaguro or Uni, it will be $60 to $90 per piece, and then you’ll feel that it is too expensive. Therefore, the total margin is secured by setting the cost rate for Kuromaguro and Uni to 80-90%, while the cost rate for Saba and Ika is set to 10-20%.

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Revision date: January 6, 2022

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Is the combination of Chablis wine and Japanese oysters match made in heaven?

White wine is generally thought to go well with fresh seafood.

For example, every Frenchman knows that Chablis wine and Belon oysters go together like peanut butter and jelly. The soil of Chablis is made of the stratum that dates back to the Kimmeridgian age and a unique characteristic is that the soil is rich in fossils of small oysters and shellfish. That is why oysters and Chablis wine are said to be the perfect pairing. However, surely there are Japanese people who sense the fishy odor when having Chablis wine and Japanese oysters (Magaki) together. Therefore, some people say that sake is definitely preferred over wine.

The reason for this is that the types of oysters in France and Japan differ.

Famous for its Belon brand name, the oyster native to Europe has a flat, rounded shell. It belongs to the genus Ostrea. To be honest, Belon oysters aren’t sweet and don’t have a distinguished flavor compared to Japanese oysters, and the salty fragrance of the sea is dulled, so it can seem less flavorful.

Meanwhile, the Japanese oyster is elongated and shaped like a raindrop. It is characterized by a smell like it swallowed the whole ocean. This is the main species farmed in Japan. It belongs to the genus Crassostrea. The taste is as if the umami components of the sea have all been concentrated together in one little shell.

Going back to pairing Chablis wine with oysters, it’s common sense in the world of flavors that items with basically similar components pair well together.

The issue lies in how wine is made. Chablis wine contains lactic acid because it is made through forced mal-lactic fermentation. Because it contains this lactic acid, it is partially fighting against the Belon oyster, which has a high glycogen content. In addition, lactic acid is called “warm organic acid”, and it has the property of becoming delicious at warm temperatures. Oysters are eaten cold, so they aren’t good for taking advantage of “warm organic acids”.

Therefore, it can be said that rather than Chablis wine, it goes well with cold organic acid white wine that is delicious when cooled to 7 or 8 degrees, for example, German Franken wine.

So then, what should be done when pairing oysters with Chablis wine?!

If you insist on pairing oysters with Chablis wine, go all out and add squeezed lemon so the citric acid will work to mask the lactic acid and succinic acid, in turn making the wine taste good even when cold. Citric acid is a “cold organic acid” that becomes delicious when cooled, and oysters rich in glycogen go well with “cold organic acid”. Cold acid-based white wine is abundant in the refreshing “cold organic acids” known as malic acid and tartaric acid. Oysters lack this cold organic acid (malic acid and tartaric acid), so adding the citric acid of lemon creates an exquisite harmony.

However, in France there was a time when a disease spread that caused the death of the Belon oyster, nearly rendering it extinct. Therefore, since the Japanese oyster has been transplanted so many times, it is said that nowadays, at least 90% are Japanese oysters hybrids of Japanese oysters.

That means the question remains among Japanese as to whether the combination of Chablis wine and oysters really is a match made in heaven or not. Personally, we’ve never heard of oysters served without lemon, so the fishy smell really isn’t an issue at all in the end.

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Revision date: January 6, 2022

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What is Toro Katsuo (Torogatsuo)?

Toro is an absolute at sushi restaurants and it’s only natural to aspire to such a position. That’s why there are so many sushi dish names that start with “Toro”. The most laissez-faire of these is Toro salmon. In this case the definition of Toro is ignored in an attempt to promote sales. Just as bad is Toro katsuo (pronounced “Toro-gatsuo” in Japanese).

Katsuo is born in the warm southern seas. When it reaches about two years old it migrates north in pursuit of Iwashi and other small fish. There are two routes taken by the Katsuo that come to the seas around Japan. One of the routes rides the Kuroshio Current (a warm current) from around the Philippines, passing by Taiwan and the Ryukyus Islands, arriving in southern Kyushu. From there the Katsuo rarely heads toward the Sea of Japan and instead the majority moves northward on the Pacific Ocean side. The Katsuo migration schedule may shift depending on the temperature of the seawater and how the schools of Iwashi and Aji (which the Katsuo feeds on) are migrating that year. The first group appears around Ishigaki Island about January, then in the seas off the shores of Kyushu and Shikoku between February and March. It then moves to the seas off of the Izu and Boso peninsulas between April and June. It reaches the open seas off the southern coast of Sanriku and Hokkaido between July and September.

Another route follows the Ogasawara ocean current from below the equator in the seas off the shore of Papua New Guinea and the seas around Micronesia to the Ogasawara Islands, along the Seven Islands of Izu and approaching the open seas off the Boso Peninsula. The route then goes northward to join with the routes mentioned above.

It’s the Modori-gatsuo that begins reverse migration toward the south at the beginning of autumn when the water temperatures start to drop. Katsuo has a strong appetite before returning south in preparation for the long trip. Unlike the light-flavored Hatsu-gatsuo, the Modori-gatsuo has plenty of fat and its body fattens up quite a bit. The main fishing locations for Modori-gatsuo are in the northern Pacific, such as the waters off the shore of Sanriku. This is the season when it is truly worthy of the name Toro katsuo when served raw, and nothing else should be called by the same name.

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Revision date: December 1, 2021

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What is Warisu?

Warisu refers to the vinegar when doing Sujime.

The fish is first washed in water, then soaked in vinegar. When working with blue-backed fish, the smell of the fish’s fat is removed from the surface with vinegar that has been used once before (and thus has a low acidity). This is called Suarai. When preparing fish with Sujime, cooled Warisu is used, made either with a 10 to 3 ratio of vinegar to ice, or the same ratio of vinegar to cold water. Vinegar with a high acidity that hasn’t been cut with water only soaks the surface of the fish (denaturing it) and the vinegar does not penetrate to the inside. In addition, if the temperature of vinegar is high, such as during summer, the skin and body of the fish soften. That’s why the vinegar is diluted (acidity is between ph 3.3 and ph 3.7) and used as chilled Warisu. After the Sujime of the topping is finished, it is important to place it in the refrigerator and allow the meat to mature slowly. For fish with strong fat, that fat oxidizes faster than the meat can mature, so it must be done very carefully.

What is Sekisaba?

Sekisaba (関サバ) and Sekiaji (関アジ) are ‘designer’ fish known for their high prices.

Of them, Sekisaba is a premium fish that can go for as high as US $50 per fish. So, what kind of fish is Sekisaba and what’s the difference between it and normal Saba (Mackerel)?

Sekisaba is a Saba caught in the Hoyo Strait with a fishing pole by a union member of the Saganoseki branch of the Oita National Federation of Fisheries Cooperative (JF Oita). In other words, Sekisaba is not a type of Saba, but a premium fish created by differentiating the fishing method.

Sekisaba started to become known all over Japan between the late 1980s and early 1990s. Until then, Sekisaba was only known as a commonplace fish that was caught incidentally with Aji and went for US $2 per fish.

However, the Saganoseki branch of JF Oita applied for the first trademark ever in the industry and then grew the brand through methods such as tagging each individual fish by hand. This resulted in recognition of its taste as “Saba that can be enjoyed even as sashimi” (while Saba is generally a fish that loses its freshness easily and not eaten raw), catapulting it to a national constituency After that, the thorough quality management and branding paid off and the price jumped to 10 times that of normal Saba.

The first difference between Sekisaba and normal Saba is that Sekisaba is caught carefully, one at a time. The use of ground bait is also banned so that the Sekisaba won’t eat anything but the natural diet (avoiding odor). Each fisher is only allowed to use fishing lures they make from fish skin or ragworms. Fish caught in this way are let out into a live holding tank on the ship and brought to the fishing port alive. After arriving at the port, the tank on the ship is checked, the fish size is looked at from the water surface and the approximate weight is measured. This method is called “Tsurugai”. This is because when the fish is placed on a scale, it struggles violently and can injure itself. The fish are allowed to calm down in the tank (called Ikekoshi) for a day at the fishing port. At the time of shipping, Ikejime is performed, in which a knife is put into gill parts, the spinal cord is cut, and then it is submerged into saltwater and the blood is let out. After that a processing method called Shinkeijime is performed in which a wire is inserted into the spinal cord to put the fish in a state of asphyxiation. Therefore, there is little damage to the fish, maintaining the freshness. When it is transported to the place of consumption, the temperature is kept at 5°C (41°F). This is because the fish does not lose its crunchiness compared to when it is cooled to 0°C. Even this is not easy to imitate.

The Hoyo Strait where Sekisaba is caught is rich in plankton, which the Sekisaba feeds on, and the flow of the tide is fast. The reason Sekisaba meat firms well and is fatty year-round is thanks to the good environment of the sea it is raised in.

If you come across a Sekisaba that so much work has been put into, try it as sashimi, not Nigiri sushi. This is because Saba, which has a peculiarity to it, is unpopular among some people. However, Sekisaba doesn’t have this off-taste and doesn’t taste like Mackerel, so even people who don’t care for fish should be able to find it tasty.

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Revision date: August 21, 2023

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What is Shiromi?

Hirame is a high-quality fish that goes for at least US $50 per kilogram. It can even exceed US $80 per kilogram, depending on the timing and the fish’s body.

Hirame is a typical shiromi (white meat fish) when winter is approaching and a great sushi topping to start off a meal. Also, the taste is so delicate that the original flavor can be cancelled out just by adding too much soy sauce. How the chef expresses this delicate taste is a tribute to his skill and something that foodies look forward to.

In the US, Hirame is often written as “halibut” on the menu of sushi restaurants. Technically the English name of Hirame is Bastard halibut. Hailbut (referring to Pacific halibut) is called “Ohyo” in Japanese. In Japan, the engawa of massive Ohyo is often used as a substitute for Hirame engawa at conveyor belt sushi, but the two are not confused for each other. There is no mistake that Hirame is related to halibut, but they are completely different species. Incidentally, the price of Ohyo is US $3 to $20 per kilogram. It is incomparably cheaper than Hirame.

Also, depending on the restaurant it may be represented in a variety of other ways such as fluke, flatfish and flounder. These terms refer to relatives of Hirame (鮃) or Karei (鰈), but do not indicate any certain species of fish. In other words, there is generally no distinction between Hirame and Karei in the US and to go even further, all white fish are thought to be the same species.

The delicious taste of fish is dependent on the distribution of fat and the amount of inosinic acid. Therefore, fish taste better in the seasons when they have fattened up. On the other hand, people have a hard time distinguishing between types of fish when comparing the tastes of the parts with less fat. The free amino acids in fish meat differ only slightly between different types of fish. In other words, the flavor of all fish is mostly the same. It is only the amount of fat and the amount of the umami component, inosinic acid, that differ between fish, so apparently even sushi chefs cannot distinguish between fish just by eating the back part, which has a low fat content.

This is part of the reason why in the US all white fish is all lumped into the same category and to top it off, the common consensus there is that white fish has no flavor.

At sushi restaurants in Japan, generally there are at least two types of white fish on offer. It is practically guaranteed that Hirame will be in stock in winter. The light flavor unique to this white meat that spreads with each bite maximizes the aroma and sweetness of the vinegared rice. Recently, white fish with high levels of fat such as Kinmedai and Nodoguro, have become standard, high-quality white fish.

The difference between how even these sorts of white fish are handled in the US and Japan is astonishing. That said, flavorless Hirame is not consumed as sashimi or sushi even in Japan. It is served in dishes with strong flavors, like carpaccio. It’s possible that delicious Hirame is just not available in the US.

Related contents: List of White flesh fish

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Revision date: July 16, 2022

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What is Masuzushi?

The origin of Masuzushi dates back about 300 years. Apparently, in 1717 it was first presented as Ayu narezushi (narezushi is a traditional food, said to be the original form of sushi and made from lactic fermentation of fish) to the third-generation feudal lord, Toshioki Maeda, by Shinpachi Yoshimura, a feudal retainer of Toyama who excelled in cooking skills. Toshioki liked the dish very much and assigned the role of vinegaring Ayu to Shinpachi. After that, it is said that the same narezushi was presented to the eighth shogun of the Tokugawa shogunate, Yoshimune Tokugawa, and that Yoshimune was extremely pleased with it.

Shinpachi’s ayuzushi was made through the painstaking process of washing salt-preserved ayu with sake, then pickling it for around 12 days, removing the rice the day before it was to be served, then adding new rice that had been flavored with sake and salt.

This transformed to the present-day Masuzushi in the late Edo period, when the amount of vinegar was increased. Hayazushi, in which vinegar is added to rice for a quick meal, became popular, and Sakuramasu started to be used instead of Ayu, These factors seem to have contributed to how it transformed into the Masuzushi we see today.

It is made by first filleting fresh Sakuramasu into three pieces and removing the skin and bones, then cutting into 3 mm thick strips. These strips are sprinkled with salt and left for 3 to 5 hours before being washed with a vinegar mixture made of salt, sugar and other seasonings (water is never used for this). The type and amount of seasonings mixed with the vinegar at this time is a secret and determines the house flavor of the restaurant or family. Sakuramasu that has marinated for 1 to 2 hours in the vinegar mixture is placed on sushi rice in the container, then held down with weights to press for several hours to complete the Masuzushi.

Long ago, it was only made with Sakuramasu caught in Jinzu River, so it was made between April and July. However, due to reasons such as a dam being built upstream and water pollution, Sakuramasu produced outside the prefecture and imported Masu (trout) is used now, and it is made year-round.

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Revision date: August 3, 2021

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