What is the ideal moisture level of the grains after soaking?

The ideal moisture level of the grains after soaking is 30-35%. This moisture content is critical because it ensures that the rice is adequately hydrated, which is essential for the subsequent processes in sake production, particularly steaming. At this moisture level, the starches in the rice grains become gelatinized effectively during steaming, allowing for optimal enzymatic activity when the koji mold is introduced. The koji mold converts starches into sugars, which are necessary for fermentation.

Moisture levels that are either too low or too high can lead to inefficient starch conversion, affecting the overall quality of the sake. For example, lower moisture levels can result in under-hydrated grains that do not gelatinize properly, while excessively high moisture levels can lead to issues such as uneven steaming or spoilage due to excess hydration. Thus, 30-35% moisture is the ideal range that balances the need for hydration and the factors critical to successful sake fermentation.