Izushi

A cold-season fish and rice ferment

Izushi is a northern Japanese preparation in which fish and vegetables are layered with rice and kōji and left to ferment. The Ministry of Agriculture, Forestry and Fisheries describes it as a lactic ferment associated with Hokkaido and other cold coastal communities from Hokkaido south into Tōhoku. Hokkaido preparations are made in late autumn or early winter and eaten around New Year and at family gatherings. The food differs from sushi seasoned with vinegar after cooking rice: fermentation is part of how izushi is made.

Fish and vegetables vary by place. The Hokkaido heritage entry lists herring, hokke, salmon, cabbage, carrot, daikon and ginger among common materials. The measured recipe printed on that page is narrower: it names small hatahata, or Japanese sandfish, with daikon, carrot, ginger, rice kōji and rice. The page says recipes differ by region and household; this fish-specific batch should not be treated as the one formula for all izushi.

The printed Hokkaido batch

The page attributes its one-barrel recipe to Mutsuko Yamagiwa of Hokkaido Bunkyo University. It lists 0.6 kg of small hatahata, 0.25 kg daikon, 25 g carrot, 10 g ginger, 5 g kōji, 20 g rice, 10 g salt, a small amount of sugar, 20 cc sake, 120 cc vinegar and bamboo leaves as needed. The printed directions call for removing fish heads, rinsing repeatedly and soaking the fish for one day in vinegar diluted five to six times. They then describe layering vegetables, salt and sugar, fish, ginger, kōji and rice in a sake-rinsed, bamboo-leaf-lined barrel, repeating the layers without gaps, adding a weight and leaving the barrel in a cool, dark place.

The MAFF page also gives a general preparation description in which fish is salted and then desalted; its printed recipe instead gives the vinegar pretreatment described above. The source does not reconcile these accounts, so this record preserves the exact printed recipe without adding an extra salt-curing or desalting step. It says an approximate 40-day period applies when making twice the listed amount. It does not specify how long the listed one-barrel quantity takes, or the barrel’s capacity.

What the source leaves open

The heritage description identifies cold fermentation, but the recipe supplies no numerical fermentation temperature, pH endpoint, salt concentration target, safety validation or tested shelf life. It also does not explain the role of vinegar in this particular version. Those gaps matter when reading a measured recipe for raw fish: listed ingredients and traditional timing do not establish a safe process. No missing controls or values are inferred here.