Carbon stable isotopic compositions of glucose and ethanol in sake after simultaneous saccharification and fermentation processes

The carbon stable isotopic composition of glucose is transferred to that of ethanol during the simultaneous saccharification and fermentation processes of sake production. However, there is limited information regarding carbon isotope discrimination between the ingredient rice and the sake components. Our fermentation experiments show that the carbon stable isotopic composition of rice is intermediate between those of glucose and ethanol in sake and do not differ significantly from those of rice koji and sake lees. Carbon isotope discrimination from rice to ethanol and from glucose to ethanol is 0.9 +/- 0.1%0 (mean +/- standard deviation, n = 18) and 1.9 +/- 0.2%0, respectively. This is approximately half of the isotope discrimination observed in grape wine due to the saccharification process during sake manufacture. Carbon isotope discrimination from ingredient rice to sake components provides valuable insights for the manufacturing process and the authentication of sake.

Automated summary

During the sake production process, the carbon stable isotopic composition of glucose is transferred to ethanol. Limited information is available regarding the carbon isotope discrimination between rice and sake components. Fermentation experiments show that the carbon stable isotopic composition of rice is intermediate between glucose and ethanol in sake, and is similar to rice koji and sake lees. The carbon isotope discrimination from rice to ethanol is 0.9 +/- 0.1%0, while from glucose to ethanol is 1.9 +/- 0.2%0, approximately half of the isotope discrimination observed in grape wine.