What useful job does a traditional wooden handai do for sushi rice after the vinegar is mixed in?

Answer: Absorbs excess moisture

Absorbs excess moisture ✓ — Right. A handai is useful because wood absorbs excess moisture while the cook cuts and fans the seasoned rice, helping the grains stay glossy instead of wet and pasty. Kikkoman explicitly says this prevents stickiness. The bowl is not decorative nostalgia; it is a passive humidity-control tool sitting right in the prep step.

Adds cedar fragrance — No. A clean handai is not meant to season sushi rice with cedar perfume or barrel flavor. Sushi rice already has a carefully balanced dressing of rice vinegar, sugar, and salt. The wooden tub's contribution is mostly texture management, not adding a new aroma that would compete with the fish.

Chills rice fastest — Not quite. The rice is cooled, but the goal is not to drive it as cold as possible. Mizkan's shaping range is roughly 30-40 C, and The Sushi Geek describes body-temperature shari as ideal. The handai helps a controlled cool-down while removing moisture, not a race to make refrigerator-cold rice.