Refractometer / Brix meter
Japanese: 糖度計（とうどけい）
Instrument measuring sugar content. Quantifies saccharification in amazake and koji.
A refractometer measures sugar concentration. In amazake, it quantifies saccharification. Handheld optical model measures with one drop on prism.
Amazake: typically 15-25 Brix — higher means more saccharification. Analog refractometers need no batteries. A step toward understanding fermentation through numbers. After use, simply rinse the prism and dry. Beyond amazake, it checks fruit jam and syrup concentration. A handy tool useful well beyond fermentation.