Japanese Matsubara-Zushi and Regional Pressed Sushi Traditions of Western Japan

Ingredients

• For the seasoned rice
• 500 g Japanese short-grain rice, cooked, fully cooled, vinegar-seasoned sushi rice
• 80 ml rice vinegar, for seasoning rice; fully absorbed before pressing
• 2 tsp caster sugar, dissolved into rice vinegar seasoning
• 1 tsp fine sea salt, dissolved into rice vinegar seasoning
• For hako-zushi (Osaka box sushi)
• 300 g medium raw shrimp, shelled, deveined, cooked just until opaque in seasoned dashi, butterflied and pressed flat between two boards to uniform thickness
• 2 eggs, made into a thin, firm omelet; sliced to fit mould dimensions
• 1 Japanese cucumber, sliced lengthwise, thin and uniform
• For saba-zushi (Kyoto mackerel)
• 400 g mackerel fillets (saba), pin-boned, skin-on, salt-cured then vinegar-cured until flesh is opaque but fish flavour and acid are both present without either dominating
• 2 large fronds Rishiri or Ma-kombu, moistened until pliable but not over-soaked; must be supple enough to wrap without crumbling or slipping
• For masu-no-sushi (Toyama trout)
• 400 g masu trout (cherry salmon) fillets, thin-sliced, uniform thickness; salted then vinegar-cured
• 8–10 bamboo leaves (sasa), fresh or rehydrated; arranged to line cedar pressing box, contributing herbal fragrance during pressing

Method

1. 1
   Season the cooked rice. Dissolve sugar and salt into the rice vinegar, then fold the seasoned vinegar through the hot rice using a cutting motion. Spread on a flat tray and fan until completely cool and all vinegar has been absorbed. The rice is ready when it holds together under gentle pressure without sticking to the hand and carries a clean, balanced acidity.
2. 2
   For hako-zushi: prepare all toppings. Cook shrimp in well-seasoned dashi until just opaque; butterfly each and press flat between two boards until uniformly thin. Prepare the omelet and slice to mould width. Slice cucumber lengthwise to even thickness. Each topping must be uniform in thickness — irregular cuts will press unevenly, producing inconsistent texture and flavour distribution across the block.
3. 3
   For saba-zushi: cure the mackerel fillets first in a generous layer of salt, then in rice vinegar, until the flesh has turned opaque throughout and the surface is firm to the touch. This is the step on which the dish lives or dies — the vinegar cure must be carried to the precise point where both fish character and vinegar acidity are fully present yet neither overwhelms the other; under-cured fish reads fishy, over-cured fish reads harsh and one-dimensional.
4. 4
   For saba-zushi: moisten the kombu fronds until pliable. Arrange a bed of seasoned rice on the kombu, lay the cured mackerel fillets over the rice in a single, even layer, then wrap the kombu tightly around the assembled block to form a firm torpedo shape. The kombu should be taut but unbroken; a kombu that crumbles was too dry, one that slides apart was over-soaked.
5. 5
   For masu-no-sushi: line the cedar pressing box with bamboo leaves, allowing them to overlap and overhang the sides. Lay the cured trout slices across the bamboo leaves in a single, even layer. Pack the seasoned rice firmly over the fish to an even depth. Fold the overhanging bamboo leaves over the surface of the rice to enclose the block. The bamboo leaf and cedar box are active contributors, not passive packaging — ensure full contact between leaf, fish, and rice.
6. 6
   For hako-zushi: arrange toppings in the oshibako in neat, precise rows — shrimp, omelet, and cucumber in separate, ordered layers over a firm base of seasoned rice. Place the lid and apply firm, even downward pressure. The pressing must be uniform; concentrated pressure at any single point produces uneven moisture and flavour distribution through the block.
7. 7
   Press all prepared forms under weight in the refrigerator. A minimum of four hours is required; overnight (8–12 hours) is the standard. The block is sufficiently pressed when it holds its shape cleanly without the mould, the layers are cohesive and do not separate when handled, and the surface is firm and cold to the touch. Do not exceed 24 hours — prolonged pressing over-acidifies the rice through continued vinegar migration from the fish.
8. 8
   Unmould the pressed sushi cold and cut with a sharp, consistently moistened knife. Wipe and re-moisten the blade between each cut. The block is correctly pressed when the knife passes through cleanly, the cross-section of each slice reveals distinct, intact layers, and the cut face holds its geometry without the layers sliding apart.