When cooked sushi rice gets refrigerator-cold, what microscopic change most directly makes it feel firmer?

Answer: Starch chains realign

Grain walls collapse — Not quite. The cited sources point to internal starch retrogradation rather than a surface-only or outer-wall change. As cooked rice cools and sits, gelatinized starch chains reassociate into a more ordered structure, and rice texture studies connect that process with higher hardness. The useful takeaway is that fridge-cold rice can harden because its starch network changes, not because the recipe changed.

Starch chains realign ✓ — Right. Cooling lets gelatinized starch chains reassociate into a more ordered structure, a process called retrogradation. Rice texture studies connect that process with higher hardness during cooling and storage. The surprise is that refrigerator-cold sushi rice is not merely cold; its starch network has begun moving back toward a firmer, more ordered state.

Surface water escapes — Not quite. This answer focuses on surface water, but the cited sources point to internal starch retrogradation during cooling and storage. Gelatinized starch chains reassociate into more ordered structures, and rice texture studies connect retrogradation with higher hardness. So the answer is a molecular rearrangement inside the cooked grain, not just water leaving the surface.