Why is Kōji mould essential in the production of sake?

Kōji mould is essential in the production of sake because it plays a crucial role in breaking down starches into sugars. This process is vital for the fermentation of sake, as yeast primarily ferments sugars to produce alcohol. The starches present in the rice used for sake are not fermentable by yeast in their original form. Therefore, the introduction of Kōji mould allows for the conversion of these complex carbohydrates into simple sugars through the action of enzymes produced by the mould. Furthermore, Kōji also releases vital nutrients, creating an environment where yeast can thrive and work efficiently during fermentation.

While the other options touch upon aspects of sake production, they do not accurately convey the fundamental role that Kōji mould plays in converting starches into fermentable sugars, which is the cornerstone of sake brewing.