Funazushi

Funazushi belongs to the oldest stratum of Japanese sushi: narezushi, in which fish was preserved by packing it in rice and letting lactic-acid fermentation do the work, a method that reached Japan from continental Southeast Asia. Salted-and-fermented fish preparations are recorded in early Japanese texts—the term appears in legal and administrative documents from the Nara and Heian periods (8th–12th centuries)—and Lake Biwa, Japan's largest lake, has long been a center of the practice; funazushi is widely regarded as the oldest surviving form of narezushi. Over the centuries, mainstream sushi diverged toward shorter-fermented and finally vinegared, unfermented forms—namanare, then the quick nigirizushi of Edo—until the rice was no longer fermented but eaten. Funazushi preserved the original method, which is why it is treated as a living ancestor of sushi rather than a regional curiosity. It remains a celebrated specialty of Shiga.

Funazushi is an acquired, powerful taste. The flesh is firm and dense, sometimes almost crumbly, with a sourness as sharp as strong vinegar and a deep, funky, fermented aroma that many compare to a pungent aged cheese. Roe-filled females (komochi) are especially prized: the packed orange eggs are granular and rich, with a cheese-like smell and a softer, almost custardy bite against the tangy flesh. It is salty, intensely savory with fermentation umami, and meant to be eaten in thin slices and small bites, often with sake or plain rice to balance it. Well-made funazushi is clean-sour and richly aromatic; a spoiled batch turns rancid and acrid rather than pleasantly sharp.

Funazushi is preserved by lactic-acid fermentation, the principle behind all narezushi. Packing the salted fish in cooked rice creates a dense, near-airless environment in which lactic-acid bacteria feed on the starch and produce organic acids; this drives the pH down to a strongly acidic level that, together with the salt, suppresses spoilage and pathogenic microbes and lets the fish keep for a year or more without refrigeration. The same acids and the enzymatic breakdown of the fish's proteins generate the intense sourness and the free amino acids that give funazushi its deep savory umami and cheese-like aroma; over the long ferment the bones soften enough to eat. The initial heavy salting both starts to preserve the fish and draws out moisture so the later rice fermentation proceeds cleanly. Because the rice is consumed by the bacteria and turns sour and pasty, in the strict traditional method it is discarded and only the transformed fish is eaten.