-
1
Clean and prepare the nigorobuna at the correct seasonal moment — when spawning cycle fat content and roe are at the desired state. Pack the fish in successive layers of salt within a sealed vessel. The fish must be fully encased with no exposed surfaces. Seal the vessel and store for a minimum of one year. The salt draws moisture progressively; the cure is complete when the flesh has firmed throughout and carries a deep, saline penetration with no trace of rawness.
-
2
Remove the salt-packed fish. Prepare cooked rice and allow it to cool fully. Layer the fish and rice alternately in a clean vessel — rice below, fish placed upon it, rice packed over and around — until the fish is entirely enclosed within a continuous rice bed. This is where the dish lives or dies: the vessel must be sealed to create a fully anaerobic environment, with no ingress of oxygen. Any failure of the seal invites unwanted moulds and destroys the lactic acid microbiome upon which authentic fermentation depends. Weight the lid and store in a cool, stable environment.
-
3
Allow rice-bed fermentation to proceed for one to three additional years. Lactobacillus species drive the fermentation; the rice absorbs fish juices, acidifies progressively, and softens to a paste. Inspect periodically for anaerobic integrity. The fermentation is complete when the fish has taken on a penetrating sourness, a cheese-like intensity, and an ammonia-edged depth, and the surrounding rice has acidified uniformly throughout.
-
4
To serve, remove the fish from its rice bed. Slice thinly at room temperature — cold service suppresses aromatic complexity. Arrange slices cleanly. Accompany with plain steamed rice to provide textural and flavour contrast. The slice is ready when its cross-section shows a fully transformed, evenly coloured flesh of uniform sour intensity with no unfermented pockets.