Kōbo no kensa

Yeast inspection

Yeast inspection is an effective method of quality control for shubo, moromi and so on. The following methods are used to examine yeast.

  1. Yeast purity.

Tests whether the inoculated yeast has been contaminated by other yeasts. Shows to what degree of purity the yeast has propagated by expressing the number of the target yeast as a percentage of the total number of yeast cells.

  1. Number of yeast cells.

The limit of yeast growth under fixed circumstances is more or less entirely constant, so the measurement of the number of yeasts cells is important in handling yeast starter and moromi.

  1. Methylene blue stain.

In order to study dead yeast cells, methylene blue stain (colouring dead yeast cells with methylene solution) is carried out. The coloured cells are given as a percentage.

  1. TTC stain.

TTC is a reagent used to test respiration-deficient cells, used in the measurement of sake yeast purity. The test measures the growth rate of colonies after three hours of propagation at 30℃in an agar culture medium containing TTC (2,3,5-triphenyl tetrazolium chloride). Sake yeast stains a dark red, respiration-deficient yeasts white, with almost all wild yeasts staining white or pale pink.