What does the term 'kasui' indicate in sake production?

The term 'kasui' specifically refers to the practice of adding water to sake after fermentation, particularly to dilute undiluted sake before it is bottled. This step is essential because most sake is brewed at a higher alcohol content, and the dilution process adjusts the alcohol level to the desired drinking strength, which can typically range from about 15% to 17% alcohol by volume.

This practice is important for achieving the right balance of flavors and aromas in the final product, making it more palatable for consumers. Dilution with water can also help to mellow the intensity of the sake, allowing for a smoother taste experience. Since 'kasui' directly pertains to adjusting the alcohol concentration, it plays a crucial role in shaping the final characteristics of the sake.

In contrast, the other choices involve different aspects of sake production: brewing rice with koji relates to the initial fermentation process, sweetness measurement is indicative of flavor profiles, and filtering processes are focused on purification. Each of these is vital in their own right, but they do not encompass the meaning of 'kasui' as dilute sake.