Kazunoko Sushi
A Comprehensive Overview of Herring Roe in Japanese Sushi Cuisine

Kazunoko 数の子(カズノコ) is the term for salted or dried herring roe or ovary. By preparing it as a whole, it forms a cohesive shape that, with a little imagination, resembles the shape of a small fish. It is a key dish in Japanese New Year's cuisine 御節料理(おせちりょうり). Furthermore, it is also a popular gift for various occasions and is considered an important part of Japanese food culture.

Kazunoko is nowadays usually found as an import product in conveyor belt sushi restaurants. It is made by removing the roe from the belly of the female herring and then drying or salting it. Hand-collected kazunoko, deposited by herring on seaweed, is called komochi kombu 子持ち昆布(こもちこんぶ) and is considered particularly high quality.

The strikingly bright yellow to golden kazunoko is predominantly bleached industrially with hydrogen peroxide. The bleaching process results in a noticeable and aesthetically pleasing color, but it compromises the taste and texture. Unbleached kazunoko is less uniformly colored and darker in hue. Its texture is firmer and the taste is more natural.^[1]

Although the crunchy texture of herring roe is pleasant, the roe itself has little taste. After curing or drying, the roe is rehydrated in water and then marinated in a mixture of soy sauce and mirin. There is a general distinction between dried, salted, and seasoned herring roe. Dried and salted kazunoko is generally rehydrated before consumption, as it would otherwise be inedible.

Ko-mochi kombu is a variation of kazunoko consisting of seaweed to which herring roe adheres. The name ko-mochi kombu is composed of three elements, each bearing a specific meaning. The character 子, pronounced as ko, stands for “child.” The characters 持ち, pronounced as mochi, derive from the verb “持つ,” meaning “to hold” or “to adhere,” and the third element, “昆布,” pronounced as kombu, refers to a type of seaweed. Kazunoko and ko-mochi kombu share the commonality of both products being derived from herring eggs. However, their preparation differs significantly. Kazunoko is obtained by extracting eggs from the belly of female herrings and then curing them in salt. In contrast, ko-mochi kombu is formed by the natural adherence of the eggs to kombu seaweed, involving already deposited eggs. Consequently, kazunoko represents the prenatal phase of eggs still in the fish's belly, while ko-kochi kombu consists of externally deposited eggs. These differences result in variations in texture, taste, and preparation methods, making both delicacies unique components of Japanese cuisine. Fresh seaweed with eggs densely and evenly distributed on both sides is considered particularly high quality.

Hoshi kazunoko refers to dried herring roe in Japanese cuisine. This delicacy consists of herring roe that is dried to achieve a specific texture and unique taste. The drying process, called hoshi in Japanese, intensifies the flavor of the roe and ensures a longer shelf life.

Preparing hoshi kazunoko requires some practice, as the roe must be soaked in a saline solution or seawater before consumption to achieve the right consistency and saltiness. It is appreciated for its crispy texture and nutty, salty flavor, which pairs well with traditional Japanese side dishes.^[2]

Shio kazunoko refers to a Japanese delicacy consisting of lightly salted herring roe. This preservation method aims to maintain the freshness and natural flavor of the roe, while also ensuring a certain shelf life through the addition of salt. The salting is relatively mild, preserving the characteristic texture and taste of the herring roe. Shio kazunoko is particularly popular during holidays and special occasions in Japan, where it is traditionally held as a symbol of fertility and a happy family life. Before consumption, it is often lightly watered to reduce the salt content and achieve the ideal flavor balance.

Enzo kazunoko is a form of preserved herring roe, made by curing in a substantial amount of salt over an extended period. This method results in a more intense flavor and longer shelf life compared to lightly salted variations. While shio kazunoko exhibits a subtle saltiness and highlights the texture and original flavor of the roe, Enzo Kazunoko is cured in a significantly higher amount of salt. This results in a stronger flavor and extended shelf life. Enzo Kazunoko requires thorough rinsing before consumption to reduce the high salt content, whereas shio kazunoko is processed with a lower salt concentration, allowing for finer adjustment to taste.

Ajitsuke kazunoko refers to herring roe that has not only been salted but also enhanced with a variety of spices and flavors. This treatment gives the roe a rich and complex taste that goes beyond simple saltiness. The specific blend of spices can vary, but often includes ingredients such as soy sauce, mirin, sake, and possibly sugar, resulting in a unique flavor profile. Ajitsuke kazunoko is particularly popular as a side dish or holiday dish, highlighting taste variety and culinary craftsmanship.

The earliest mention of herring roe dates back to 1463 during the Muromachi period (1336-1573) in the records of the Yamashina family, the Yamashina Raiki 山科家礼記. The Yamashina family was responsible for the Emperor's affairs, and it is documented that they purchased herring roe for the court in Kyoto. Their records indicate that Ashikaga Yoshiteru, the 13th shogun, ate herring roe. Another mention of kazunoko is found in the records of Toyotomi Hideyoshi, who attended a meal in 1594 at the residence of Maeda Toshiie, where herring roe was served. It is also said that Tokugawa Yoshimune, the 8th shogun of the Tokugawa shogunate, ensured that herring roe became part of the traditional New Year's meal.^[3]

The term “kazunoko” combines kazu, meaning “number,” and ko, meaning “child.” In the Japanese New Year tradition, kazunoko symbolizes the wish for fertility and prosperity, specifically the desire for many descendants in the new year. This delicacy is appreciated not only for its unique taste and texture but also for its deep symbolic meaning in New Year's celebrations. It represents the wish for a rich blessing of children and symbolizes the hope for growth, happiness, and the continuity of the family.

In the language of the Ainu, the indigenous people of Japan, herring is called kado, and since it colloquially means the 'children of herring' (kado no ko), it is simply referred to as kazu-no-ko.^[4] In the past, kazunoko was also affectionately referred to as the “yellow diamond” (kiiroi daiya 黄色いダイヤ).^[5]

Depending on the origin and species of the mother fish, kazunoko differs in texture. The difference in texture is attributed to the environment of the spawning grounds. The spawning grounds of Pacific species in North America and the waters around Japan are rich in seaweed. The species spawning there use this seaweed to deposit their eggs. To prevent the eggs from being washed away by the waves, they are firmly connected and sticky. This surface texture gives the eggs their crunchy consistency. The eggs of the Atlantic herring do not need this sticky property, as this fish species deposits its eggs on sandy ground. Consequently, the roe has a higher water content, resulting in a softer texture.

Herring is caught in various fishing grounds around the world and can be broadly divided into two categories: Pacific herring (taiheiyō nishin 太平洋ニシン), caught off the coasts of the Pacific, and Atlantic herring (taiseiyō nishin 大西洋ニシン), caught off the coasts of the Atlantic. Recently, more and more herring from the Sea of Okhotsk are being imported to Japan.^[6]

As catches in the waters around Japan have declined, companies processing kazunoko in Japan have attempted to transfer processing technology and know-how to overseas fishing areas. Most of the herring catches processed into kazunoko today come from the eastern central Pacific, from San Francisco to Alaska's Bristol Bay.^[7]