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1
Clean the crucian carp thoroughly. Pack the fish completely in coarse salt — every cavity, every surface — and leave under weight in a sealed vessel for 2 to 6 months in a cool environment. The salt draws moisture from the flesh. The fish is ready to proceed when the flesh is firm throughout and has lost a significant proportion of its original weight in liquid.
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2
Remove the fish from the salt cure. Rinse. Pack the fish into a clean vessel in alternating layers with plain cooked rice, pressing each layer firmly to eliminate every air pocket. Seal the vessel and store at a consistent temperature of 12–15 °C. This is where the dish lives or dies: insufficient salt in the preceding cure allows putrefaction rather than fermentation; any air pocket in the rice layers here allows the wrong bacteria to dominate; and any fluctuation in temperature during the months and years ahead risks compromising the controlled lactic-acid environment. Lactic acid bacteria from the environment will colonise the rice and begin the slow transformation of the fish proteins into amino acids.
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3
Leave undisturbed to ferment for a minimum of one year; the full traditional form requires three years. Monitor that the vessel remains sealed and the temperature stable. As fermentation advances, the rice softens to an almost paste-like consistency and the vessel will emit an increasingly pungent, lactic-sour, ammoniac smell — sharp, like a very strong aged cheese. This progressive deepening of aroma confirms active, correct fermentation.
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4
After the chosen fermentation period, open the vessel. The rice will be soft and paste-like. The fish flesh will be transformed: proteins broken down to amino acids, intensely umami-rich, pungent and lactic-sour in character. In the original tradition the rice is discarded and only the fish is eaten; in some modern practice the fermented rice paste is also served. The fish is done when the aroma is complex and fermentation-sharp rather than rotten — the distinction requires knowledge of the process.