【Reading】こおりじめ

【English Name】Korijime

Koejime is a treatment method in which caught fish are immersed in ice-filled seawater and slowly killed in a low-temperature environment. It is often classified as a type of "nojime" (field-killing).

Compared with ikejime, in which the brain or medulla is processed one fish at a time, the common evaluation is that its effect in terms of preserving freshness is somewhat inferior. However, an effect of reducing stress on the fish's body is recognized, and compared with leaving them untreated, it can suppress quality deterioration.

This method is especially useful at sites where a large catch occurs all at once. Applying individual ikejime treatment to every landed fish is not realistic, and this method of rapidly cooling them with ice water has taken broad root in fishing fields. There is also a view that regards koejime as a form of ikejime, and the boundary between the two remains ambiguous with no established theory.

The flavor of sushi has an inseparable relationship with the freshness of the fish. The scientific effects of ikejime—such as preserving ATP (adenosine triphosphate) and suppressing bacterial proliferation through blood draining—are well known, but koejime, too, has taken root in fishing fields as a practical means of freshness management, bearing an indispensable role in daily operations.