Japan — kasuzuke developed alongside sake production, making use of the substantial volume of kasu produced as a byproduct. Narazuke from Nara (Nara's sake brewing tradition is over 1,000 years old) is among Japan's oldest documented fermented foods.
Kasuzuke is the pickling of fish, meat, or vegetables in sake kasu (酒粕) — the lees (pressed solids) remaining after sake is pressed from fermented rice mash. The kasu contains residual sugar, amino acids, yeasts, and alcohol; it acts simultaneously as a preservative, a flavouring agent, and a tenderising medium. The most celebrated kasuzuke: Narazuke (奈良漬け, from Nara Prefecture) in which vegetables are pickled in sake kasu for months to years; and sakekasu-marinated fish such as gindara no kasuzuke (black cod in sake lees), one of Nobu Matsuhisa's most celebrated dishes.
Kasuzuke delivers the concentrated flavour of sake — the fermented rice sweetness, the amino acid depth, and the alcohol's penetrating character — embedded into the food itself. Grilled kasuzuke fish develops an extraordinary caramelised crust from the sugar and amino acids, while the interior remains moist and infused with sake character. The flavour is simultaneously sweet, savoury, slightly alcoholic, and deeply umami — a uniquely Japanese combination of fermentation and Maillard reaction.
Sake kasu preparation: the kasu is mixed with sugar, mirin, and salt to create a spreadable paste. Fish marination: fish is buried or coated in the kasu paste for 24–72 hours (longer for firmer fish like black cod). The sugar and amino acids in the kasu caramelise dramatically during cooking (grilling or broiling), producing the characteristic amber-caramelised surface. The alcohol penetrates the fish, denaturing surface proteins and acting as a preservative while the amino acids begin flavour development. Vegetable Narazuke: cucumbers, melon, or daikon are salted first, then transferred to progressively older and stronger sake kasu baths over months — the final product is intensely flavoured, amber-coloured, and deeply complex.
Black cod (gindara) is the perfect kasuzuke fish because its high fat content and firm texture absorb the kasu magnificently and its flesh remains moist during the high-heat grilling required for proper caramelisation. Nobu's Miso Black Cod (which uses white miso rather than kasu) demonstrates the same principle and achieved global fame. For Narazuke, the traditional Nara method uses the kasu from Nara's famous sake breweries — the best Narazuke pickles are aged 3–5 years and taste of sake, caramel, and deep vegetable umami.
Using low-quality sake kasu — the quality of the kasu (from a premium junmai sake vs. basic futsushu) dramatically affects the flavour. Not wiping excess kasu before grilling — kasu burns quickly and produces bitter char. Under-marinating fish — 24 hours is the minimum; 48 is better. Using fatty fish without accounting for the fat's interaction with the kasu's sugar — very fatty fish (salmon) can caramelise too quickly and burn before the flesh cooks through.
Preserving the Japanese Way — Nancy Singleton Hachisu; Nobu: The Cookbook