What is the purpose of koji in sake production?

Koji plays a crucial role in sake production primarily by aiding in the fermentation process. It is made from steamed rice that has been inoculated with the mold Aspergillus oryzae, which is essential for saccharification. This mold breaks down the starches present in the rice into sugars, which are necessary for fermentation. Without koji, the yeast, which is responsible for converting sugars into alcohol, would lack the sugars needed to thrive and produce alcohol. Therefore, the introduction of koji not only facilitates the conversion of starch to sugar, but it also contributes to the overall complexity and depth of flavor in the sake, making it an indispensable element of the brewing process.

While koji can have various impacts on the final product, such as influencing sweetness and flavor, its primary function is indeed to support fermentation. Other options such as enhancing acidity, adding sweetness, or providing color do not directly relate to the specific, pivotal role koji plays in the conversion of starches to sugars during sake brewing.