What is the primary purpose of the "Shubo" in sake brewing?

The primary purpose of the "Shubo" in sake brewing is to start fermentation. The Shubo, also known as the yeast starter or koji mash, is a crucial component in the fermentation process as it establishes an environment where yeast can thrive and convert sugars into alcohol.

During the brewing process, the Shubo typically consists of a mixture of steamed rice, koji (mold-inoculated rice), water, and yeast. This mixture promotes the rapid growth of yeast, allowing for a robust fermentation starter that can be added to the main fermentation mash, known as the "moromi." The successful development of the Shubo ensures that fermentation proceeds effectively, resulting in the desired characteristics of the final sake.

In contrast, aging sake is performed during a later stage of production and involves storing the finished product to enhance its flavors. Filtering sake is a separate process aimed at clarifying the final beverage, while extracting flavors from koji pertains to the initial stages of sake for enzymatic activities but is not the primary function of the Shubo. The focus of the Shubo is specifically on initiating and facilitating yeast growth for fermentation.