Why do sushi cooks season rice while it is hot, then let it cool before shaping nigiri?

Answer: Hot mixing distributes seasoning; cooling makes rice comfortable to shape by hand.

Hot mixing removes the vinegar’s acid; cooling kills bacteria before shaping. — Cooling does not kill bacteria, and mixing with hot rice is not intended to remove all the vinegar’s acidity. The cooking steps prepare flavor and handling temperature, not sterilization. Safe holding still depends on appropriate time, temperature and acidification controls.

Hot mixing distributes seasoning; cooling makes rice comfortable to shape by hand. ✓ — Freshly cooked hot rice is mixed with vinegar seasoning so it is distributed evenly. Gentle cutting and folding while fanning cools the rice and helps remove surface moisture. After the excess heat has dissipated, it can be shaped comfortably by hand; cooling here does not mean it must become refrigerator-cold.

Cold rice absorbs vinegar best; shaping piping-hot rice prevents sticking. — The usual sequence is to season freshly cooked hot rice, not chill it first for better absorption. Shaping piping-hot rice is uncomfortable and does not provide a special protection against sticking. Gentle handling preserves the grains as the rice cools.