Kyoto Oshizushi Pressed Box Sushi Tradition

Ingredients

• For the cured mackerel
• 2 Pacific mackerel (masaba), whole fillets, skin on, pin-boned; use Japanese Pacific masaba, not Atlantic varieties
• 40 g fine sea salt, for first-stage salt cure
• 200 ml rice vinegar, for second-stage vinegar cure
• For the kombu sushi rice
• 500 g short-grain Japanese sushi rice, washed and drained
• 600 ml cold water, for cooking
• 1 kombu sheet, approx. 10 cm square; for infusing sushi vinegar
• 80 ml rice vinegar, for sushi seasoning
• 30 g caster sugar
• 10 g fine sea salt, for rice seasoning
• To assemble
• 4–6 bamboo leaves (sasa), rinsed; for lining the oshibako if following Toyama masu-no-sushi tradition, or for wrapping finished block

Method

1. 1
   Lay the mackerel fillets skin-side down on a tray. Scatter the 40 g fine sea salt evenly over the flesh. Leave uncovered at room temperature for 30–60 minutes. The surface of the fish will appear visibly wet and the flesh will feel slightly firmer to the touch. Rinse under cold water and pat completely dry with paper towels.
2. 2
   Place the rinsed, dried fillets flesh-side down in a shallow dish. Pour the 200 ml rice vinegar over them; they should be nearly submerged. Cure for 20–40 minutes. The flesh will turn opaque-white at the edges while retaining a translucent rose at the centre. The combined effect of the two-stage cure should read as mild and rounded — not sharply saline. Lift the fillets, pat dry, and peel away the fine transparent outer skin from the flesh side in one sheet.
3. 3
   Steep the kombu sheet in the 80 ml rice vinegar for 20 minutes, then remove. Dissolve the 30 g caster sugar and 10 g salt into the kombu-infused vinegar. Cook the washed rice in 600 ml cold water using your standard absorption method. While the rice is still hot, transfer to a wide non-metallic tub and fold in the kombu sushi vinegar with a cutting motion. Fan continuously until the rice reaches room temperature and carries a faint gloss. Do not press the rice until it is fully cool — hot rice produces a gummy, over-compressed texture.
4. 4
   This is where the dish lives or dies. Line the oshibako (standard Kyoto box: 27 × 9 × 4.5 cm) with dampened cling film or bamboo leaves if using the Toyama convention. Lay the cured mackerel fillets skin-side down in a single even layer to cover the base precisely. Pack the cooled sushi rice firmly over the fish to approximately 2 cm depth, pressing into the corners with wet fingers so no air pockets remain. Set the lid in place and apply firm, uniform downward pressure — weight the lid with a heavy board and additional weights. Insufficient or uneven pressure will cause the block to fall apart when sliced.
5. 5
   Refrigerate under pressure for a minimum of 2 hours; 8–24 hours produces the firmer, more integrated flavour characteristic of Kyoto saba oshizushi. Remove from refrigerator 20–30 minutes before serving — cold suppresses rice flavour and makes the texture excessively firm.
6. 6
   Invert the box onto a clean board. The block should release cleanly as a single unit. Using an extremely sharp knife dipped in cold water, slice into 10–12 precise rectangles with a single drawing cut per slice — do not saw. A correctly pressed block cuts cleanly through compressed rice and fish in one motion; any shredding of the surface indicates either a dull blade or insufficient pressing time.