Category: Edomaesushi

What is the difference between Real and Imitation wasabi?

A photo of Imitaion wasabi
This is imitation wasabi served with uramaki.

When most people think of wasabi, they picture a bright green paste with a strong, nose-tingling heat. In reality, what is served in most sushi restaurants around the world—including in the U.S., Europe, Asia, and China—is usually imitation wasabi.

This is not because restaurants want to mislead customers, but because real wasabi is incredibly difficult to grow and very expensive. The Wasabia japonica plant needs pure spring water, cool temperatures, and several years of careful cultivation, which makes large-scale production nearly impossible. As a result, genuine wasabi is rare even in Japan, and much harder to find abroad.

A photo of Imitation wasabi
Imitation wasabi is a food product primarily made from horseradish. It contains added coloring, flavoring, and thickening agents that give it the appearance and taste of real wasabi.

Imitation wasabi, made from horseradish, mustard, and green coloring, became the practical solution. It is affordable, easy to store, and widely available, which has allowed sushi culture to spread and become popular worldwide. Without this substitute, sushi culture might not have grown as quickly outside Japan.

Even in Japan, most wasabi served at conveyor-belt sushi chains or sold in supermarkets is not 100% hon-wasabi (hon means real). There are powdered forms that must be mixed with water, and smooth pastes packaged in tubes. Their compositions vary: some include a small amount of domestically grown wasabi rhizome, others add mustard powder for extra sharpness, and many rely primarily on horseradish. In other words, “imitation wasabi” in Japan exists on a spectrum—from blends with real wasabi to products made almost entirely from substitutes.

By contrast, at high-end sushi restaurants and traditional ryotei in Japan, chefs freshly grate real wasabi rhizomes on sharkskin graters and serve it directly with sushi. These chefs deliberately choose authentic wasabi because it brings out the natural character of the fish and rice. Its fleeting heat, subtle sweetness, and refreshing aroma work in harmony with the sushi rather than overpowering it. In other words, real wasabi is not just a condiment—it is an essential element that allows the true flavor of the ingredients to shine.

In recent years, a few farms in the United States—in places like Oregon, North Carolina, and California—as well as in Europe, China, and other parts of Asia have begun cultivating real wasabi. However, the same challenges remain: it cannot be mass-produced, so supply is very limited.

So while most people around the world—and even many in Japan—have only encountered imitation wasabi, it exists for very practical reasons. And when diners finally taste freshly grated real wasabi, they often discover a surprisingly delicate, even slightly sweet flavor unlike anything they expected.

For travelers visiting Japan, tasting real wasabi at a sushi restaurant or ryotei is a unique culinary experience. It is an opportunity to appreciate the subtlety and harmony of authentic Japanese cuisine—something that cannot be fully replicated elsewhere.

Related contents:

What is Yamawasabi?

What is wasabi?

The Birth of Edomae Sushi Through Soy Sauce

A photo of soy sauce
The main ingredients of soy sauce are soybeans, wheat, and salt.

The Deliciousness of Nigiri Sushi and the Role of Soy Sauce

The appeal of nigiri sushi lies in the balance between the vinegared rice

’s gentle acidity and the seafood’s natural umami. Soy sauce elevates this harmony, acting like a quiet but essential partner in the background—a supporting role without which sushi would feel incomplete.

So-called Kansai-style sushi, such as oshizushi, bozushi, and hakozushi, which developed from preserved foods, involves seasoning not only the vinegared rice but also the sushi toppings. Therefore, it can be eaten without soy sauce. However, Edomae sushi uses fresh ingredients and values the inherent flavor of those ingredients. This necessitated a soy sauce that wouldn’t compromise the natural taste of the ingredients but rather enhance it.

Soy sauce contributes more than taste. It also helps neutralize the fishy odor that vinegar alone cannot remove. For instance, in hikarimono like kohada, saba, and aji, even a light brush of soy sauce softens the smell and polishes the flavor.

Beyond flavor and aroma, soy sauce also plays a role in preservation. Just as vinegar and salt protect sushi from spoilage, soy sauce has long been recognized for its bacteriostatic properties. In this way, it supported the development of Japanese cuisine, which relies on raw ingredients even in Japan’s humid climate.

Whether through its color, taste, fragrance, or hygienic qualities, soy sauce is woven into the very foundation of Japanese culinary culture.

Traditional Soy Sauce in Edomae Sushi

Edomae sushi originally used seafood caught in Tokyo Bay, but from the Edo period onward, fish such as tuna were also brought in from distant waters. These were often marinated in soy sauce in a technique called zuke. The name itself comes from this marinade, and to this day, sushi shops that uphold Edomae traditions still serve maguro zuke. Thanks to modern freezing and storage methods, fresh tuna is available year-round, so zuke is no longer a necessity—but its deep, mellow flavor endures.

In the past, soy sauce was rougher and less refined than today. To suit their needs, sushi chefs would cook and season it, creating nikiri shoyu (“simmered soy sauce”). This is typically made by gently simmering soy sauce with 10–20% mirin, sometimes with sake, bonito stock, or water. After about 30 minutes, when bubbles form, the heat is turned off. The word nikiri—literally “simmered to completion”—is said to come from this step.

Although improvements in modern soy sauce mean some shops no longer use nikiri, many traditional Edomae sushi restaurants still brush it onto their nigiri, just as they continue the practice of zuke.

Among simmered toppings (nimono) like anago, shako, and hamaguri, another essential sauce is tsume (or nitsume). Made by reducing the simmering liquid of anago or hamaguri with soy sauce, mirin, and sugar until it becomes a rich glaze—about one-tenth its original volume—tsume has been perfected in each restaurant’s own style.

Traditionally, tsume is prepared when high-quality anago arrives. The head and bones are simmered to create a flavorful broth, which is strained and then combined with soy sauce, mirin, and sugar. It is slowly reduced over half a day into a glossy sauce. The choice of soy sauce here is critical, and many sushi chefs say that the depth of a restaurant’s tsume reflects its true character.

Conclusion

In sushi, soy sauce is far more than a condiment. It balances flavors, refines aromas, preserves freshness, and embodies tradition. The delicate ways in which it is used—through zuke, nikiri, or tsume—are a testament to the craft of Edomae sushi and remain central to the essence of sushi culture today.

What is Aka shari?

A photo of aka shari
This is nigiri sushi with aka shari.

The “aka” in aka shari means “red” in Japanese, while “shari” refers to the vinegared rice used in sushi. Literally, it means “red vinegared rice,” but it doesn’t actually refer to bright red rice; instead, it denotes vinegared rice with a slightly brownish hue.

Why is it called “red”?

Typical vinegared rice is made by mixing cooked white rice with rice vinegar or grain vinegar. These vinegars are clear or pale yellow and don’t significantly change the rice’s color. As a result, the general understanding worldwide is that vinegared rice is white. Occasionally, artificially colored vinegared rice—such as blue or purple varieties—can also be seen.

By contrast, aka shari is made with red vinegar or black vinegar. These are dark brown liquids, and when mixed with rice, they produce vinegared rice with a light brown tint. Red vinegar was traditionally used in Edomae sushi, which originated in the Edo period, and this practice gave rise to the term “aka shari.” Its opposite is “gin shari.” While “gin” means silver, in this context it refers to pure white sushi rice.

However, making sushi rice exclusively with red or black vinegar results in a color that is too dark and an aroma that is overpowering, leading to an unbalanced taste. Although these vinegars are rich in umami components like amino acids, using them alone disrupts the overall harmony and can be polarizing in flavor. For this reason, sushi chefs commonly blend them with rice vinegar or grain vinegar. In fact, vinegar producers even sell blended vinegars specifically designed for vinegared rice.

Just as with other fermented foods, not everyone appreciates the flavor of aka shari made with red or black vinegar. While some chefs use it to emphasize the traditional prestige of Edomae sushi, it doesn’t always suit sushi that relies on a refreshing acidity.

Summary

Aka shari refers to sushi rice made with red vinegar, a hallmark of Edomae sushi. Its distinctive flavor and color add depth, but it is challenging to handle and not to everyone’s taste. How red vinegar is blended with other vinegars, and how the final rice harmonizes with sushi as a whole—this is where the craftsmanship and philosophy of the sushi chef truly shine.

What is the difference between Sabazushi and Battera?

Both sabazushi and battera are types of oshizushi made with mackerel. Oshizushi is made by layering vinegared rice with vinegared mackerel and shiro-ita konbu, then pressing the mixture into a wooden mold. Mackerel has been abundant in Japan since ancient times, which led to the development of this dish as a practical preserved food.

There are clear differences between Sabazushi and Battera, so let us explain them.

A photo of sabazushi
The appearance of sabazushi

Sabazushi is said to have originated in the Edo period. Mackerel is salted and transported from its place of origin in Wakasa to Kyoto, where it arrives after 2 to 3 days, by which time the seasoning is just right. This salted mackerel is used to make Sabazushi. Even today, with the development of refrigeration technology, it remains popular with many people and is also a local dish of Kyoto. There are also long-established sushi restaurants that have been in business for generations. Additionally, Sabazushi can be found in other regions such as Hyogo, Hiroshima, and Wakayama, which have adopted the dish from Kyoto.

Sabazushi is prepared using a unique method. First, the air is removed from the vinegared rice to extend its shelf life. Then, the vinegar-marinated mackerel is formed into sticks with a cloth or bamboo mat. Finally, shiroita konbu or rausu konbu is placed on top to prevent the mackerel from drying out. Only half of the mackerel is used so that the thickness of the flesh is evident. The cross-section is rounded, which is why it is also called bozushi (bo means “stick”).

A photo of battera
The appearance of battera

Next, Battera is a type of Oshizushi made by placing thinly sliced mackerel marinated in vinegar and shiroita konbu simmered in sweet vinegar on top of vinegared rice. It is typically shaped using a square mold. The mackerel is cut with a knife to minimize waste, resulting in an almost uniform thickness.

Battera is said to have been invented in 1894 by Tsunekichi Naka, the founder of Sushi Tsune, a sushi restaurant in Osaka. At the time, Sushi Tsune was selling Oshizushi made with Konishiro (Gizzard Shad), which was commonly caught in Osaka Bay. Due to its popularity, the traditional method using a cloth became insufficient for production, so a wooden, boat-shaped mold was used instead.

Customers reportedly referred to the mold as “bateira,” a Portuguese word meaning “boat,” which evolved into “battella.”  Over time, this name further transformed into “Battera.” As the price of Konishiro (Gizzard Shad) rose, mackerel was adopted as an alternative, and due to its ease of shaping, square molds became the standard.

In summary,

Sabazushi: Use a bamboo mat to shape the fish into a round form, using thick slices of mackerel left whole. The cross-section has a rounded shape.

Battera: Shaped into a square using a wooden mold, thinly sliced mackerel is arranged evenly. The cross-section is square.

Sabazushi is a traditional regional sushi centered around Kyoto, while Battera is a type of sushi that became popular among the general public in Osaka.

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The image of the boat-shaped wooden mold used when making battera

What is the difference between Chirashizushi and Barachirashizushi?

A photo of chirasihizushi
This is what most people think of when they hear the word chirashizushi.

Recently, I came across an image on social media of Barachirashizushi made by an American sushi chef. I was surprised to see that Barachirashizushi, a dish traditionally made only by a few sushi restaurants that uphold the Edomae-style, had been created by a sushi chef outside Japan. However, it was labeled as Chirashizushi, which I found disappointing, so I will explain the difference.

The term “chirashizushi” (or “chirashi sushi”) originates from the act of scattering various ingredients over or within vinegared rice and is sometimes referred to simply as “chirashi.” Generally, “Gomokuzushi” refers to vinegared rice mixed with ingredients, while “chirashizushi” refers to vinegared rice topped with arranged ingredients. However, these terms are not strictly distinguished. The names may vary depending on the region (e.g., Kanto or Kansai) and generation.

First, let’s explore the origin of chirashizushi. The term “barazushi” appears here, but it is different from barachirashizushi.

Barazushi, a type of sushi from Okayama, is said to date back to the early Edo period. At that time, the feudal lord of Okayama Domain, Ikeda Mitsumasa (1609–1682), promoted frugality and simplicity. He issued the “One Soup, One Side Dish Edict,” which restricted side dishes to one item other than soup.

They finely chopped ingredients such as simmered shiitake mushrooms, kanpyo (dried gourd strips), and carrots and secretly mixed them into the rice. According to one story, sushi ingredients were placed at the bottom of a box and covered with seasoned rice to disguise them as a simple meal. The box was then flipped over just before serving.

As “Barazushi” spread throughout Japan, a style of scattering the ingredients on top of the vinegared rice rather than mixing them in was developed, and this became known as “Chirashizushi.”

Now, let’s look at the difference between chirashizushi and barachirashizushi, focusing on the names used in sushi restaurants in Tokyo.

a photo of Chirashizushi
The appearance of Chirashizushi

In Tokyo sushi, specifically Edomae sushi, Chirasushizushi refers to a dish where sushi toppings used for Nigiri sushi are arranged on top of vinegared rice (also known as Namachirashi, Fukiyosechirashi, or Edomaechirashi). However, in regions outside the Tokyo area, Chirashizushi generally refers to a dish where seasoned ingredients are mixed into vinegared rice and decorated with shredded omelette and seaweed (also known as Gomokuzushi or Barazsuhi). This is just my personal opinion, but I think that even in Tokyo, the latter is called chirashizushi.

Dishes made with plain white rice rather than vinegared rice are generally called seafood bowls. Sushi restaurants do not serve bowls of plain white rice (they cannot), but some restaurants call dishes made with vinegared rice seafood bowls. In my personal opinion, most seafood bowls served outside of sushi restaurants are made with plain white rice.

A photo of Barachirashizushi
The appearance of Barachirashizushi

Additionally, a dish with randomly arranged sushi toppings on vinegared rice is called “barachirashizushi.” Some traditional sushi restaurants in Tokyo offer two types: chirashizushi, which is primarily served in-store, and barachirashizushi, which excludes toppings that are not suitable for takeout and can be taken home.

Incidentally, chirashizushi made with sushi ingredients is not typically prepared in Kanto-style households. More precisely, it may include decorative toppings such as ikura (salmon roe), tobiko (flying fish roe), and steamed shrimp; however, the standard ingredients are dried shiitake mushrooms, lotus root, carrots, snow peas, and shredded omelet.

Related contents

Types of sushi

How to Make Sushi Rice for chirashi sushi!

The role of green onions in sushi

A photo of Ao-negi
Other names for ao-negi include ha-negi, sho-negi, and bannō-negi.

We think foreigners may be unable to tell the difference between Japanese green onions just by looking at them. There are two main types, but even though they are the same onion, they have different names, which can be confusing. In the Kanto region and northern Japan, shiro-negi (Japanese leeks) are commonly eaten, while in western Japan, ao-negi (green onions) are the mainstream variety. Green onions used as a condiment in udon and soba noodles are also Japanese leeks in the east and green onions in the west.

A photo of Naga-negi
Other names for Naga-negi include Shiro-nrgi and Nebuka-negi.

Onions with more white parts are called “Nebuka-negi (根深ネギ),” while those with more green parts are called “Ha-negi (葉ネギ).” In Eastern Japan, the term “negi” simply refers to Nebuka-negi (also called Naga-negi or Shiro-negi), which is grown by mounding soil around the plant as it grows to protect it from direct sunlight, resulting in a strong flavor and thick stems. Other types are distinguished by specific names such as “Wakegi,” “Asatsuki,” “Bannō-negi (also called sho-negi),” and “Kujo-negi.” In western Japan, the thin Ha-negi grown in the sun is called “Ao-negi,” and Nebuka-negi is sometimes referred to as “Shiro-negi” or “Nebuka.”

In summary, the word negi in Japanese cuisine is a broad term that can refer to several varieties: Ao-negi (青ネギ), common in western Japan; Naga-negi (長ネギ), more popular in eastern Japan; and their subtypes such as Bannō-negi (万能ネギ), an improved cultivar of Ao-negi, and Kujo-negi (九条ネギ), a Kyoto specialty. These variations can be confusing to foreigners, but they reflect how regional food culture has shaped the way green onions are used in Japanese cooking.

Onions Commonly Used in Sushi Restaurants

In Japanese sushi restaurants, several types of onions play important supporting roles in flavor and presentation. The most common are Bannō-negi (万能ネギ), a versatile fine green onion; Ao-negi (青ネギ), the standard leaf onion; Naga-negi (長ネギ), a long Welsh onion often used as Shiraga-negi; and Me-negi (芽ネギ), the tender young sprout onion. Each type has its own distinct characteristics and culinary uses.

Bannō-negi, often translated as “fine green onion,” is actually an improved cultivar of the broader Ao-negi group. Compared to standard Aoba-negi, it is thinner, softer, and milder, making it especially suitable as a garnish for sushi or sashimi.

By contrast, Naga-negi has a thick white stalk. In sushi, it is often shredded into fine strips called Shiraga-negi (白髪ネギ), which are placed on top of fatty fish to balance richness with a refreshing sharpness. By the way, Shiraga (meaning “white hair”)-negi refers to the white part of Naga-negi, sliced thinly like white hair.

Another variation is Me-negi, which are delicate and visually appealing. They provide a crisp texture and a subtle, grassy fragrance that complements lighter sushi toppings.

Together, these different forms of onions demonstrate how sushi chefs carefully choose the right variety to balance flavor, texture, and presentation.

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Condiments for sushi

Types of whales used as sushi toppings

A photo of minke whalesashimi
Sashimi is a standard menu item at whale specialty restaurants.

It has been six years since Japan withdrew from the International Whaling Commission (IWC) and resumed commercial whaling. Many consumers had hoped that whale meat would become cheaper and appear on dinner tables. This is because whale meat is a nutritious and versatile ingredient that can be used in a variety of dishes. However, the amount of whale meat available in circulation has decreased compared to the era of research whaling. What exactly were the Japanese government and the whaling industry trying to protect?

On the other hand, the three countries strongly pushing for a “whale hunting ban” in Japan are the United States, Australia, and New Zealand. Why is Japan not allowed to engage in commercial whaling when Iceland and Norway are permitted to do so? Such inconsistencies also exist.

In fact, very few Japanese people actually want to eat whale meat. According to a survey by Greenpeace, 95% of Japanese people do not particularly want to eat whale meat. It is said that the average annual consumption of whale meat per person in Japan is now 40 grams. It was quite a challenge to find images of whale sushi in our saved files.

In other words, whales may now be used as political and economic tools, transcending issues such as human food and the environment.
To put it bluntly, it may be the fault of a few members of parliament elected from constituencies with many whaling-related interests and hundreds of bureaucrats who do not want to lose their budgets.

This article is simply to show that whale sushi exists as part of Japanese food culture. Although rare today, whale occasionally appears as sushi neta (topping). So, what kinds of whale are actually used for sushi? Let’s take a closer look.

1. Minke Whale (Balaenoptera acutorostrata　Lacépède, 1804)

A photo of Minke whale　nigiri sushi
The appearance of Minke whale nigiri sushi

Minke whales in the northern hemisphere are about 8 meters long. Seen from above, their heads are pointed at the tip. There is a white patch on the upper center of the pectoral fins. The dorsal fin, about 30 cm high, is located toward the rear of the body and is often clearly sickle-shaped. The back is black, the sides are gray with a blurred pattern, and the lower jaw and abdomen are white.

It generally feeds on krill, small squid, and fish. It filters its food through bristle-like baleen plates, made of keratin. The Japanese name for the minke whale is higekujira, which means bearded whale.

  • Description: A relatively small baleen whale, measuring about 7–10 meters in length.

  • Use: The most commonly caught species in Japan’s commercial whaling, widely utilized for sushi toppings, sashimi, and bacon-style preparations.

  • Flavor: The red meat is tender with little odor, making it one of the more approachable types of whale meat.

2. Bryde’s Whale (Balaenoptera edeni Anderson, 1879)

Bryde’s Whale is a close relative of the Sei whale. It was named “Nitarikujira” (meaning “similar whale”) because it resembles the Sei whale. It grows to a maximum length of about 15 meters and is slightly smaller than the Sei whale.

  • Description: A medium-sized baleen whale, usually 12–15 meters long, larger than the minke whale.

  • Use: Its red meat is served as sushi or sashimi, while fatty cuts and tail meat are often cooked.

  • Flavor: The red meat has a richer taste with a pronounced umami and iron-like character.

3. Sei Whale (Balaenoptera borealis Lesson, 1828)

Sei whales are baleen whales belonging to the family Balaenopteridae. They migrate across the open ocean in schools of sardines, feeding on them, which is how they got their name.

Two subspecies are recognized: the northern hemisphere subspecies (B. b. borealis) and the southern hemisphere subspecies (B. b. schlegelii). They are distributed in the southern Indian Ocean, the North Atlantic and South Atlantic, and the North Pacific and South Pacific.

Its body is slender and spindle-shaped, with a sickle-shaped dorsal fin. The dorsal color is dark blue, the ventral color is light blue, and there are blurred patterns in between. The head is V-shaped, enabling it to swim at high speeds. The maximum body length is approximately 18 meters.

  • Description: A baleen whale that grows 12–18 meters long. In the past, it was more frequently caught, but today only limited numbers are harvested.

  • Use: The lean red meat is used for sushi or sashimi, while fattier portions are processed into bacon or fried dishes.

  • Flavor: The meat is tender and relatively mild, with a clean, elegant taste.

4. Sperm Whale (Physeter macrocephalus Linnaeus, 1758)

Sperm whales are distributed worldwide from the Arctic to the Antarctic, with the largest populations found in deep ocean waters. Male sperm whales grow to a length of 15 to 20 meters and weigh between 40 and 60 tons. Their body color is blackish gray, but it becomes whiter with age. In particular, the head tends to become whiter. The dorsal fin is mountain-shaped, with several ridges extending from the rear toward the tail fin. The surface of the body, except for the head, is rough and uneven.

  • Description: A toothed whale and one of the largest whale species, reaching 15–20 meters or more in length.

  • Use: Rarely used as sushi. Instead, its distinctive fatty tissue is made into “toothed whale bacon” or other processed foods.

  • Flavor: The fat has a unique aroma and a very rich, heavy taste.

Types of whale meat

Saezuri

Saezuri is very fatty, and the taste and texture differ between the root and tip of the tongue.  It has a deep umami flavor and is used in simmered dishes and oden. It is one of the most popular delicacies of whale meat.

Onomi

The back section from the dorsal fin to the tail, with fat marbled like snowflakes (shimofuri). Considered the most delicious part of whale meat, it is also known as whale Otoro.

Unesu

The white, accordion-shaped part running vertically from the lower jaw to the navel is called Une, and the red inner part is called Sunoko. These two parts together form Unesu. It has a soft, gelatinous texture and is one of the most popular whale meat cuts, cherished for generations.

Bacon

Bacon is a processed food made by salting and smoking the part called Unesu.

For reference.

Sudachi vs. Kabosu: How Sushi Chefs Use Citrus to Enhance Flavor

A photo of sudachi vskabosu
The appearance of sudachi and kabosu

Sudachi is small in size with an intense aroma and a sharp, refreshing acidity. In contrast, kabosu contains more juice and offers a milder sourness, giving it a soft flavor that enhances other ingredients without overpowering them. Sudachi is about the size of a golf ball, while kabosu is about the size of a tennis ball.

【Nutritional value of kabosu】
Vitamin C
Citric acid
Potassium
Pinene
Limonene

【Nutritional value of sudachi】
Sudachitin
Vitamin C
Citric acid
Potassium
Beta-carotene
Vitamin E
Calcium
Dietary fiber
Polyphenols

At sushi restaurants, these characteristics are carefully utilized. Sudachi is often paired with delicate toppings such as white fish or shellfish, where just a drop can add a refreshing fragrance and highlight the clean flavors of the fish. It is particularly valued when the sushi chef wants the citrus aroma to leave a memorable impression or to give a lighter, fresher finish to the sushi.

Conversely, using sudachi repeatedly in an omakase course can mask the flavors of the sushi toppings.

Kabosu, on the other hand, is chosen when the balance of flavors is more important than fragrance alone. Its gentle acidity and abundant juice make it suitable for richer or fattier fish, grilled items, or simmered dishes, where it softens heaviness and provides an elegant aftertaste.

A photo of Kikabosu
The appearance of Kikabosu

Aged kabosu (Kikabosu), with its mellow and rounded aroma, is sometimes used to enhance the sophistication of high-end sushi. For example, a light drizzle of kabosu over sushi made with the mild-flavored pen shell (Tairagi) elevates the shellfish to a higher level. Sudachi or young kabosu, however, are too pungent and would merely serve as a simple accent.

In short, sushi chefs distinguish between the two by using sudachi when they want to highlight aroma and freshness, and kabosu when they wish to bring harmony and subtlety to the flavor.

【Related contents】

Condiments for sushi

What is ultra-low temperature freezing?

A photo of ultra-frozen tuna
The appearance of ultra-frozen tuna

The freezer compartment of a household freezer typically operates at -18°C. However, in practice, due to factors such as how often the door is opened and closed, the temperature often only reaches around -12°C. While this is cold enough to freeze water, it does not freeze the core of the food, so it may appear frozen at first glance. Proteins, enzymes, and lipids remain unfrozen, causing the taste and texture of the food to deteriorate significantly within a few weeks.

On the other hand, ultra-low temperature freezing can freeze all the components of fish meat, suppressing protein decomposition and stopping lipid oxidation. This makes it possible to store food for up to six months. All living organisms begin to age and deteriorate after death, eventually leading to oxidation and decay. The temperature that can stop this process is the world of ultra-low temperature freezing at -42°C.

Inhibition of enzymatic protein degradation

Under normal conditions, proteins that have ceased activity at room temperature undergo enzymatic degradation. For example, the proteins in freshly caught fish are in a high-molecular-weight state. Through enzymatic degradation, they break down into lower-molecular-weight compounds, advancing the aging process. If this process progresses too far, decay occurs.

Additionally, fish have a high water content of 70%, making them age much faster than livestock meat. Therefore, the key is to quickly cool the fish to ultra-low temperatures after catching them and then thaw them while maintaining the aging process.

Inhibition of fat oxidation

What is commonly referred to as “freezer burn” occurs when the fat naturally present in food rises to the surface and oxidizes, causing the color to turn yellowish and the appearance and taste to deteriorate. To prevent this, it is essential to prevent the food from coming into contact with air. Furthermore, by storing it in an ultra-low temperature environment, the oxidation process itself can be almost completely halted.

Inhibition of microbial proliferation

Even at the -18°C environment of a household freezer, microbial proliferation can be largely suppressed. However, for complete inhibition of all types of microbial growth, ultra-low temperatures are ideal.

Real-world applications

Ultra-low temperature freezing is already widely used in the seafood industry. At Tokyo’s Toyosu Market, premium tuna is stored and transported at -60°C to preserve its deep red color, fatty texture, and fresh taste for overseas shipments. In Hokkaido, Pacific saury is frozen at -50°C immediately after being caught on specialized vessels, allowing them to be enjoyed months later with near-fresh quality. Some Japanese supermarket chains use -45°C freezing for salmon fillets, enabling them to offer sashimi-grade products all year round while minimizing quality loss.

In sushi restaurants, anago (saltwater eel) is often purchased in bulk when prices are stable, stored at ultra-low temperatures, and thawed to maintain quality and cost efficiency. Likewise, ikura (salmon roe) is typically prepared in autumn, its peak season, and frozen for year-round use, ensuring consistent flavor and texture regardless of the season.

The fact that a 10,000-year-old mammoth excavated from Siberian permafrost was still edible after being cooked is a testament to the capabilities of ultra-low temperatures.

What is the difference between Ikura and Sujiko?

A photo of sujiko
The appearance of sujiko

At first glance, Ikura and Sujiko look quite similar — both are salmon or trout roe — but they differ in preparation, flavor, texture, and how they are eaten. Here’s a closer look at their differences.

What is Ikura?

The word ikura comes from Russian, meaning “fish roe” or “small grains.” In Russia, it can refer to various types of roe, including caviar and cod roe. In Japan, however, ikura generally refers to salmon or trout roe, and in the fishing industry, it often means only salmon roe.

Ikura is made from mature salmon roe that is removed from the egg sac, separated into individual eggs through a mesh, and then seasoned — typically with salt or soy sauce. The grains are large, bursting in the mouth with a satisfying “pop,” releasing rich, buttery flavor. Because of its beautiful appearance and texture, ikura is commonly used for sushi, rice bowls, and various appetizers.

What is Sujiko?

Sujiko is made from immature (Not just before laying eggs) salmon roe that is salted while still wrapped in the membrane of the ovary. The eggs remain connected like a string (suji: 筋 in Japanese), which is where the name comes from. Since the eggs are less mature, the grains are smaller than those of ikura, and the texture is more dense and creamy.

There are two main ways to season sujiko:

  1. Traditional salting (塩漬け) – The roe is salted to draw out umami, then salted again to finish the process. Freshness is critical; roe processed immediately after the fish is caught will be less salty and have better texture, while roe processed later will taste saltier and lose some texture.

  2. Soy sauce marinating (醤油漬け) – A modern method that uses soy sauce which does not darken the roe, preserving its bright red color.

Historically, sujiko was considered a very salty preserved food and was thought to pair poorly with vinegared rice, so it was rarely used in sushi. However, with the rise of low-salt and soy sauce–marinated sujiko, it has started to appear in sushi and other creative dishes.

Key Differences

  • Egg maturity – Ikura: mature eggs / Sujiko: immature eggs

  • Grain size – Ikura: larger / Sujiko: smaller

  • Preparation – Ikura: eggs separated / Sujiko: eggs kept in membrane

  • Texture – Ikura: bursts in the mouth / Sujiko: creamy and dense

  • Use – Ikura: sushi, donburi, appetizers / Sujiko: rice topping, onigiri, and now occasionally sushi

Both ikura and sujiko are symbols of autumn in Japan. Knowing the differences will help you appreciate their unique qualities — and choose the perfect roe for your meal.

What is Koku?

A photo of stew
There are many secret ingredients in stew.

Koku is a comprehensive sensory experience derived from the combined stimuli of taste, aroma, and texture in food. It refers to a phenomenon characterized by the complexity of these stimuli, further enhanced by a sense of spatial expansion and lingering persistence.

Just as taste is defined by the five basic categories of sweetness, saltiness, bitterness, sourness, and umami, Professor Toshihide Nishimura of Kagawa Nutrition University explains that koku can also be described through three fundamental elements: complexity, mouthfulness, and lingeringness.

While these three terms are individually recognized internationally in relation to flavor, there is no direct English equivalent that fully captures the nuance of the Japanese concept of koku when these elements are combined.

The first element, complexity, can be objectively evaluated based on the diversity of chemical compounds present in a food. For instance, fermented foods like soy sauce and miso develop hundreds of additional compounds as they age—meaning a batch aged for two years will typically have much greater complexity than one aged for only one year. Similarly, foods that are cooked for extended periods, such as stews, tend to develop a more intricate flavor profile due to the formation of a wider range of substances, which enhances the sense of koku.

The second element, mouthfulness, is closely tied to retronasal aroma—the aroma that travels from the back of the throat into the nasal cavity during chewing and swallowing. Retronasal aroma plays a critical role in how we perceive flavor. This becomes particularly evident when we catch a cold: with nasal congestion impairing our sense of smell, foods suddenly seem flavorless. In fact, the olfactory system is considered more advanced than the gustatory system in distinguishing fine differences. For example, when chewing vinegared rice, the aromas of vinegar, kelp broth, and seaweed gradually rise through the back of the throat into the nasal passages. Aromatic molecules linger on the mucous membranes of the nasal cavity, allowing the brain to continue interpreting them as part of the overall taste experience.

The third element, lingeringness, is often enhanced by the presence of fat. Fat readily absorbs and retains aromatic compounds, allowing them to adhere to the mucous membranes of the tongue and nasal passages, thus prolonging the flavor experience. While we often describe fatty foods as “rich and flavorful,” it’s important to note that fat itself is tasteless and odorless. The perceived flavor comes from the wide range of compounds that dissolve into the fat during cooking, creating a complex and lasting impression.

However, not all taste and aroma compounds in food are present at concentrations high enough to be consciously perceived. Here, the concept of a threshold becomes crucial—the minimum concentration at which a compound can be detected by the senses. Many flavor and aroma molecules exist below this threshold. While they are not individually detectable, they interact synergistically with other components to subtly but significantly shape the overall flavor impression.

These undetectable compounds function like hidden flavors. Rather than asserting themselves directly, they enhance the definition of other flavors and contribute to a balanced and harmonious profile. In this sense, they can be considered koku-enhancing substances that strengthen the depth, complexity, and persistence of the taste experience.

For example, a small amount of yuzu peel added to miso soup, a pinch of salt concealed in a simmered dish, or the synergistic effect of glutamic acid and inosinic acid in kelp-based broth—all of these contribute not through obvious presence, but by shaping the overall flavor, expanding the taste on the palate, and enriching the lingering aftertaste we associate with koku.

Thus, koku is not simply a “rich flavor” but a nuanced sensory phenomenon created by the interplay of clearly perceptible and imperceptible flavor elements. It emerges from thoughtful ingredient selection, careful cooking techniques, controlled aging, and subtle enhancements such as “secret ingredients.” All these components work together to create a dish with true koku.

This is why koku is so difficult to translate directly into English. It is not just a taste, but a layered sensory experience with temporal and spatial dimensions, lying at the very heart of Japanese cuisine. Understanding koku provides valuable insight into the richness of Japanese culinary culture and the refined craftsmanship that brings its flavors to life.

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What is the difference between eel sauce and conger eel nitsume?

A photo of anago nigiri sushi
Besides anago, nitsume is brushed onto sushi toppings that have been simmered in a flavorful liquid, like shako and hamaguri.

In Japanese culinary terms, “nitsumeru” (verb) refers to the process of reducing the liquid content of a sauce containing seasonings by boiling off the moisture, thereby concentrating the flavor and increasing its thickness. Both “eel sauce” and “conger eel nitsume” are sauces made by reducing the liquid content through boiling.

First, you need to understand the difference between eel and conger eel.
In Japanese, the word “unagi” generally refers to a freshwater eel. The scientific name is Anguilla japonica Temminck & Schlegel, 1846. On the other hand, the word “anago” generally refers to the conger eel. Its scientific name is Conger myriaster (Brevoort, 1856).

While both eel sauce and conger eel nitsume are made by reducing liquid through boiling (the process known as nitsumeru), only the latter is traditionally referred to as “nitsume” in sushi restaurants.

So, what is the fundamental difference between them?
Eel sauce (known as unagi sauce or unagi no tare) is a rich, sweet soy sauce-based sauce that is ideal as a dip or drizzling sauce. It does not actually contain any eel ingredients, but it is a sweet, sticky sauce that is perfect as a topping for sushi rolls and other dishes.

“Eel sauce” can refer broadly to both mass-produced sauces and artisan sauces made by eel restaurants. The basic method for making eel sauce is to mix mirin and soy sauce and heat it. Various ingredients such as sake, sugar, tamari soy sauce, water amber, honey, dashi, and potato starch (commercial products often contain thickening agents) are added to create a unique flavor.

Incidentally, most traditional eel restaurants make their eel sauce using only high-quality mirin and soy sauce. This gives the eel a beautiful glaze and subtle sweetness when grilled, as well as a clean aftertaste, which is why it is considered a craftsmanship.

When making kabayaki, the process of applying eel sauce is repeated multiple times. The components of the eel sauce combine with the umami of the eel to create a deeper, more complex flavor. In addition, applying the sauce and grilling it causes chemical reactions such as the Maillard reaction and caramelization, which further enhance the appetizing flavor.

While you can easily buy eel sauce at the market, it’s incredibly easy and tasty to make at home. Eel sauce can be used as a seasoning for other dishes if there is any left over, but it is primarily a sauce specifically made for making kabayaki. By the way, kabayaki is a fish dish where the long-bodied fish is filleted, the central bone removed, skewered, grilled, and then coated with a thick sauce before being grilled again. In Japan, when people say “kabayaki,” they are usually referring to “unagi kabayaki.” Other ingredients used include hamo and anago.

Nitsume is brushed onto nigiri sushi made with anago, shako, shellfish, and other toppings. In sushi restaurants, it is often abbreviated as “tsume.” There are several methods for making nitsume, including reducing the cooking liquid from simmered conger eel, or simmering the head and bones of conger eel to extract the broth, then adding seasonings and reducing it further. In other words, nitsume contains components of conger eel.

Compared to anago, unagi is more flavorful, fatter, and meatier. Moreover, unagi is considered a higher-quality delicacy in Japan and is therefore more expensive. In terms of taste, unagi has a richer, more intense umami flavor. The common opinion is that anago, because of its lighter taste, harmonises better with soured sushi rice and is therefore the preferred choice for making nigiri sushi.

As a side note, while nigiri sushi with eel is common in the Kansai region, eel is not used as a sushi topping in Edomae sushi. Therefore, Edomae sushi restaurants do not serve unagi nitsume.

In summary, unagi (eel) sauce is made by eel restaurants, while anago (conger eel) nitsume is made by sushi restaurants. Eel sauce does not contain eel components, while conger eel nitsume contains conger eel components.

What is Sujime?

A photo of sujime
The fish is marinated in vinegar.

Sujime (酢締め) is a traditional preparation method in which fish is first salted to draw out moisture (Shiojime) and then lightly marinated in vinegar. It is widely used as a sushi topping.

However, the techniques used for Sujime today differ significantly from those of the Edo period. Differences include the amount of time the fish is left with salt and the duration it is soaked in vinegar. Until around the 1980s, it was common practice to soak fish such as mackerel and horse mackerel in vinegar for an extended period. In modern times, thanks to advanced refrigeration technology, fish such as horse mackerel (aji) can now be eaten raw without concern. As a result, the time the fish is salted has been shortened to just a few minutes. Once moisture begins to appear on the surface, it is carefully rinsed off with water. Rather than soaking in vinegar, the fish is quickly dipped, more like a gentle rinse. The goal is to retain the natural flavor of the fish, requiring a delicate and refined touch.

Fish suitable for Sujime are those with a robust umami flavor and a distinctive aroma that can stand up to the acidity of vinegar. Typical examples include blue-backed fish like mackerel, Spanish mackerel, sardines, and gizzard shad. Depending on the case, white-fleshed fish such as barracuda, red seabream, and filefish may also be prepared as Sujime.

There are three main reasons why Sujime is used in sushi restaurants.

The first is preservation. Vinegar has strong antibacterial properties, and before the advent of refrigeration, Sujime was a way to prevent spoilage and extend the shelf life of fish. Vinegar kills bacteria on the surface of the fish, helping to keep it hygienic. Even today, in sushi where raw consumption is the norm, Sujime remains valuable for enhancing food safety.

Second, Sujime plays a key role in reducing unpleasant odors and refining flavor. Blue-backed fish are rich in fat, particularly unsaturated fatty acids found between the skin and flesh. These fats are prone to oxidation, which can cause a strong fishy smell. Additionally, the flesh of fish contains trimethylamine oxide, a naturally odorless compound that, over time and through bacterial action, turns into trimethylamine, which has a strong odor. Eventually, ammonia is also produced, intensifying the smell. Since Trimethylamine is alkaline, treating the fish with acidic vinegar neutralizes it, effectively reducing odor. A quick dip in vinegar removes unwanted smells and balances the umami and acidity, resulting in a more refined taste.

A photo of sujime kohada
The vinegar causes the proteins in the fish to denature.

Finally, Sujime enhances both the flavor and texture of the fish.
When vinegar is added to fish, the proteins are denatured. The pH of fresh raw fish is around 6, but when it is into vinegar and the pH becomes more acidic. The gaps between the myofibrils decrease because of vinegar, tightening the flesh. This creates a texture and mouthfeel distinct from raw fish.

As the pH continues to drop below 4, the myofibril protein starts to dissolve in the acid, so the flesh becomes soft and mushy. But if the fish is salted and tightened before putting it in vinegar, the myofibrils do not dissolve and remain intact, so the flesh continues to tighten. This is why vinegared- marinated fish looks white.

Furthermore, the acidity of vinegar stimulates the taste buds on the tongue, creating a synergistic effect that brings out sweetness and umami. Even with a short vinegar marinade, a mature aroma and depth are added, giving blue-backed fish such as kohada and mackerel a deep, “mature flavor.”

Sujime is not merely a preservation technique; it is a skilled process that brings out the best qualities of the fish. It is one of the key steps in refining the sushi experience to perfection.

What is Namero?

Namero: A Fisherman’s Delicacy from Chiba

A photo of Namero
The appearance of Namero

Introduction

Namero (なめろう) is a traditional local dish from the coastal areas of the Bōsō Peninsula in Chiba Prefecture, which faces the Pacific Ocean.
This region has long been blessed with an abundance of fresh seafood, especially horse mackerel (aji), available year-round.
Originating as a fisherman’s meal, namero was devised to be easily prepared on the unsteady decks of fishing boats, making the most of freshly caught fish.

Main Ingredients and Preparation

The basic recipe involves finely chopping horse mackerel together with miso, green onions, ginger, and sometimes shiso leaves,
then mincing everything together until it becomes sticky and paste-like.
While horse mackerel is commonly used, other blue-backed fish such as sardines, pacific saury, flying fish, yellowtail, and even squid or bonito
are also popular depending on the season and locality.

The use of miso instead of soy sauce has a practical origin—it’s less likely to spill on a rocking boat.
The miso also helps neutralize the strong aroma of oily fish, enhancing only their natural umami flavors.
It is said the name “namero” comes from the phrase “so delicious you’ll want to lick the plate clean.”
Another theory is that the sticky texture makes it hard to scrape off the plate, so you’d have to “lick” it off to finish it.

Misconceptions and Variations

Namero is sometimes confused with “tataki (タタキ),” another chopped fish dish, but they are quite different.
Tataki is usually lightly chopped and often uses soy sauce and vinegar, whereas namero is more thoroughly minced and flavored with miso,
creating a smoother and more cohesive texture.

Over time, regional variations and creative adaptations of namero have emerged.
One notable example is sanga-yaki (山家焼き), a grilled version of namero.
Legend has it that fishermen used to pack leftover namero into abalone shells and grill it in mountain huts while working inland—hence the name “sanga,” meaning “mountain house.”

Another beloved version is “mago-cha (まご茶)” (literally, ‘grandchild tea’), a rustic ochazuke-style dish where namero is placed on hot rice and doused with warm dashi broth.
The name has two possible origins: one being that the dish could be eaten quickly without hesitation (“mago-mago” meaning to fumble),
and the other being that it’s so tasty you’d want to share it with your grandchildren.
The addition of dashi slightly cooks the fish, offering a delightful change in texture and flavor.

Conclusion

Namero is a dish that truly captures the culinary heritage of coastal Chiba, transforming simple, fresh fish into a flavorful and nutritious meal.
With its wide adaptability, regional roots, and deep umami taste, it continues to charm both locals and visitors alike.
Today, it is served as a tsumami (appetizer) in izakayas and sushi restaurants.
Whether enjoyed raw, grilled, or as a comforting bowl of ochazuke, namero remains a timeless symbol of Japan’s rich seafood culture.

What is Arai?

A photo of Koi arai
The appearance of Koi arai

Arai is a traditional Japanese sashimi technique in which raw seafood is rinsed in cold or ice water. Also known as “洗鱠” or “洗魚”, this method is especially popular during the summer months for its refreshing taste and texture.

How Arai Is Prepared

In this technique, thinly sliced or shredded fish is placed in a strainer set over a bowl of ice water and washed until the flesh firms and warps. Some chefs also use running water for the rinsing process. The purpose of this rapid chilling is to stimulate the muscle fibers, causing them to contract and tighten, resulting in a firmer texture and improved mouthfeel.

Benefits of the Arai Method

Washing the fish removes surface proteins and lipids, effectively reducing unwanted odors—often caused by the oxidation of fats—and producing a cleaner, lighter taste. Arai is especially well-suited for seafood that has a strong aroma, high fat content, or soft flesh.

Common Seafood Used in Arai

  • Freshwater fish: Carp (koi) is the most well-known example.
  • Shrimp: Live kuruma shrimp are sometimes rinsed instead of served raw, offering a firmer texture than odorigui (live sashimi).
  • Saltwater fish: Japanese sea bass (suzuki), black sea bream (kurodai), and redspotted grouper (akou or kijihata) are commonly prepared as arai to remove their pungent coastal aroma (known as iso-kusasa).

Historical Context

During Japan’s period of rapid economic growth in the postwar Showa era, marine pollution led to concerns about fish having a “petroleum-like” odor. Suzuki was especially affected and often prepared as arai to mask the smell. This historical context helped establish Suzuki no Arai as a quintessential seasonal summer dish in Japanese cuisine.

Freshness Is Essential

Fish used for arai must be extremely fresh and ideally still alive at the time of preparation. After death, fish rapidly lose ATP (adenosine triphosphate), the energy molecule responsible for muscle contraction. Once ATP is depleted, rinsing in cold water no longer causes the muscle fibers to contract, rendering the technique ineffective. The act of washing forcibly removes ATP and induces contraction, resulting in a firmer texture.

A Seasonal Delicacy

The brief rinsing also helps wash away surface fat, balancing the richness of fatty fish and resulting in a crisp, clean flavor. This quality makes arai not only a method of preparation but also an expression of culinary seasonality and refinement, offering a moment of cool relief during Japan’s hot summer months.

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