Koikoku is the name of a dish of round sliced carp stewed in miso soup. Koku of koikoku comes from kokusho, a kind of soup with miso, and koikoku used to be one variation of kokusho. Kokusho used to be cooked popularly until the Edo period. It is said not only carps but eels, crucian carps, soft-shelled turtles, salamanders, and various wild fowls used to be used to make kokusho. It was a dish of fish or meat with strong smell stewed in thick miso soup. Kokusho almost disappeared after the Edo period, and only koikoku, a variety of kokusho with carp, remains up until today.
Koikoku is mainly eaten in eastern Japan in the inland area of Honshu. As described in Shotaro IKENAMI's "Onihei Hankacho," it seems to have been a favorite dish of Edo people. It is said koikoku helps a mother after giving birth to milk well.
On January 6, 1746, 篠澤佐五右衛門包道, an official liaison (warimoto) of Iwamurata, Saku County, Shinshu, presented koikoku to Toba FUKUSHIMA, a low-ranking Shinto priest of Ise Jingu Shrine. The document is kept by Akiyoshi SASAZAWA, the eighth descendant. The Sasazawa family has run an inn from the Edo period, and they have an event every January 6th at this inn to reproduce koikoku in the original style (the birthday of Sakukoi (Saku carp)).
In Hiroshima Prefecture there is a rite to cook carp for a person one loves to communicate the affection, which has been handed down till today.
How to cook koikoku
Remove the scales from a carp and cut in round slices.
Place the carp on the colander and pour hot water to remove the smell.
Heat water, sake, miso, and sugar in a pot, and after it boils add carp.
Lower the flame after it boils again, skim off the scum, and stew for about an hour.
Serve carp and soup in a bowl and add strips of green onion and citron. You may sprinkle sansho powder or shichimi togarashi (a mixture of red cayenne pepper and other aromatic spices) if you like.
In some regions carp is cooked without being scaled.
It becomes richly flavored and tastes better if cooked with the head of carp.
In addition to carp sometimes other ingredients are added such as tofu (bean curd) and daikon (Japanese radish).