Which yeast is considered to be one of the most important in the sake industry, formerly known as the main ginjo yeast?

Yeast Number 9, also referred to as Kyokai No. 9, is indeed one of the most significant strains used in the sake industry, particularly noted for its role in the production of ginjo sake. This yeast strain is esteemed for its ability to produce fragrant and fruity esters, which are characteristic of high-quality ginjo saké. Its clean fermentation profile helps enhance the complexity of flavors while maintaining a delicate balance, making it ideal for brewers aiming to create premium sake.

Furthermore, Yeast Number 9's consistent performance across varying fermentation conditions has made it a favorite among sake brewers, encouraging its adoption in many breweries around Japan. This yeast strain contributes to the distinctive characteristics that define modern ginjo sake, which has become increasingly popular among consumers for its aromatic qualities.

In contrast, the other choices do not have the same historical significance or impact on the ginjo style of sake. For example, Meiri Kobo is a sake brewery and doesn't refer to a yeast strain, while Miyama Nishiki is a rice type rather than a yeast. Muroka, on the other hand, refers to a processing method for sake, specifically unfiltered sake, rather than a yeast strain.