The Brix value obtained by enzymatic digestion of steamed rice based on national brewer rice unified analysis methods is assumed to be important for Japanese sake brewers to estimate the digestibility of newly cropped rice and re-establish sake brewing procedures based on this value. Here, we explored the relationship between Brix and temperature during the rice developmental period using sequential earlier-period rice analysis data gathered from the 2002–2019 crop years for 24 rice varieties as well as data from the Automated Meteorological Data Acquisition System（AMeDAS）. The Brix of Gohyakumangoku significantly differed depending on the production district. The Brix of Ginpu, Suisei, and Kitashizuku cropped in Hokkaido were positively correlated with the mean and maximum temperatures during the 15 days after heading（DAH） of rice. In all 17 rice cultivars for sake brewing, except for that cropped in Hokkaido, the Brix value was clearly and negatively correlated with maximum temperature during the middle and later stages over a month of rice development, rather than the average temperature during 30 DAH, depending on the rice cultivar. In some table rice cultivars, we did not observe a correlation between the Brix and temperature during the rice developmental period. Thus, by utilizing the optimized temperature conditions and the term after heading of rice, the Brix of the rice cultivars for sake brewing could be estimated more precisely.

The pyruvic acid content of sake mash was determined using a commercial determination kit, “Simplified Measurement Kit for Pyruvate”（Shinyo-Giken-Kogyo）. The very rapid optimum reaction of our kit was measured at 25℃ for 10 min at 440 nm. The measurements obtained with this kit correlated well with those obtained using a medical kit, “Determiner PA Kit”（r＝0.9809）. This assay can be used for the immediate detection of pyruvic acid in sake mash by the naked eye. The new technique by our kit is very rapid, simple, and does not require expensive equipment. This analysis is thus ideal for the assessment of filtration for sake mash in breweries.