Tsukudani(佃煮?) is small seafood, meat or seaweed that has been simmered in soy sauce and mirin. High osmotic pressure preserves the ingredients. Its name originates from Tsukudajima, the island (in present-day Chūō, Tokyo) where it was first made in the Edo period. Many kinds of tsukudani are sold. Traditionally made tsukudani is preservable and has been favored as a storable side dish in Japanese kitchens since the Edo period.
Tsukudani can be made with kombu or wakame seaweeds. It is usually eaten with steamed rice as a flavoring agent since the flavor is very intense (approximately 1 Tbsp for one bowl of rice). Finished tsukudani is served chilled from the refrigerator where it takes on a gelatinous texture.