“Tosaurara”, a variety of rice suitable for sake brewing grown in Kochi Prefecture, was cultivated with the goal of reducing the white core size of “Kazenaruko” and improving the cracked rice ratio. In order to confirm achievement of these goals, cultivation tests, brewing suitability tests, and brewing tests were conducted using “Tosaurara”. The yield of “Tosaurara” was 112% higher than that of “Kazenaruko” in the cultivation tests. The 1000 kernel weight was 0.9 g less than that of “Kazenaruko”, but the white core rate was about 30% lower and the white core was smaller. In the rice polished test, the cracked rice ratio of “Tosaurara” was higher than that of “Kazenaruko” in the 70% polished test, but in the 50% polished test, the cracked rice ratio was 4.2%, which was much lower than that of “Kazenaruko” at 10.6%, showing an improvement. In small-scale brewing tests, “Tosaurara” had the same sake brewing properties as “Kazenaruko”, which is highly rated for sake brewing properties, and showed a characteristic of a higher acidity in brewing tests at 50% polished rice. These results indicate that “Tosaurara” has improved white core rates and cracked rice ratios compared with “Kazenaruko”, has brewing characteristics comparable to “Kazenaruko”, and is a new variety suited to the environment in Kochi Prefecture.
Caproic acid and caprylic acid are considered to be the cause of a fatty odor, which is an off-flavor of sake using ethyl caproate high-producing sake yeast. In this study, a simple and rapid method with a solvent extraction method and mass spectrometry gas chromatography(GC/MS) was developed for determining caproic acid and caprylic acid. Aliquots(1 mL) of sake were mixed with n-amyl alcohol as an internal standard. Solvent extraction was carried out by adding 3mL ethyl acetate, and the ethyl acetate in the upper layer was applied to GC/MS. Under optimized conditions, the detection and quantification limits of caproic acid and caprylic acid in sake were 0.1 and 0.5 mg/L, respectively. The calibration curve for caproic acid in sake was linear over the range of 0.8-118.4 mg/L with R2=0.9999. The calibration curve for caprylic acid in sake was linear over the range of 0.9-44.0 mg/L with R2=0.9995. The pretreatment time required for preparation of the GC/MS measurement solution was less than 1 hour in 20 samples and GC/MS analysis time was about 10 minutes per sample. This analytical method can accommodate many samples quickly and can be applied to sake mash. The method revealed that 36 ginjo sake samples for contest exhibition contained caproic acid in the range of 19.1-44.1 mg/L and caprylic acid in the range of 4.0-9.3 mg/L. During storage of the Ginjo sake samples, caproic acid and caprylic acid concentrations did not change significantly in about 3 months regardless of storage temperature(−4℃~25℃). There was a clear difference in caproic acid production even after a short incubation period between ethyl caproate high-producing sake yeast and traditional yeast.