Japanese oyster nigiri

Japanese oyster (Kaki)

【Nigiri sushi: Kai】
Kaki (Japanese oyster) is widely distributed in Japan, as well as on the Korean Peninsula and in China. Its shell length is about 5 to 8 cm. Its shape is highly variable because it lives attached to rocks or reefs, but it is usually irregularly elongated and triangular. The season lasts from fall to winter, when glycogen levels are at their highest, and the flavor becomes especially rich.

The main production areas are Hiroshima, Miyagi, and Iwate prefectures, and the size and color vary depending on the region. Hiroshima-grown oysters are large and milky white, while those from Miyagi and Iwate are medium-sized and bluish black.

In many countries, it is common to simply squeeze lemon juice over raw oysters and eat them as is, sometimes even drinking the remaining liquor in the shell. However, when raw oysters are used in gunkan-maki or nigiri sushi, the moisture released from the flesh quickly soaks into the vinegared rice and nori seaweed, disrupting the balance of texture and flavor. Therefore, when serving them as sushi toppings, it is common practice to prepare them first by lightly cooking them in sake or soy sauce, or by using the kobujime (kelp-curing) method to draw out umami while removing excess moisture.

Oysters prepared in this way feature a smooth, silky texture and a rich, pronounced umami flavor. The technique requires gently shaping the sushi to avoid crushing the moisture-rich flesh, making it a true showcase of a sushi chef’s skill.

Although oysters were not originally a traditional topping in Edomae sushi, they have been adopted as a relatively recent addition as ingredient availability has expanded and production techniques have improved. Oysters began to appear in sushi restaurants claiming to serve Edomae-style sushi in the late Showa period, and gradually became part of a broader trend of incorporating a wider variety of seafood beyond traditional sushi toppings.

Scientific name: Magallana gigas (Thunberg, 1793)

【Nutritional information】
The reason oysters have gained popularity as a sushi topping is that it is said that the active ingredients in oysters are good for health. For example, glycogen is nourishing and can help prevent arthritis. They also contain minerals such as iron, manganese and copper as well as vitamins B1, B2 and B12, contributing to a therapeutic diet. Furthermore, zinc is effective in improving and preventing taste disorders. Finally, taurine can help improve liver function.

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(Revision date: June 16, 2026)