Yeast purity (Kobo junndo)

Yeast purity (koubo junndo) is an indicator of what proportion of the yeast found in a sample taken during sake production, such as the shubo (yeast starter) or moromi (fermentation mash), is the cultured yeast that was added. Specifically, it shows how many cells of the added cultured yeast are present for every 100 yeast cells in the sample. Yeast purity is tested mainly with the TTC staining method or with a method using β-alanine medium, which allows the purity of the yeast to be measured accurately. High yeast purity affects the stability of brewing and the flavor of the sake, so it is an important element in sake quality control.