Abstract: The dynamic variation of organic acids in fermented grains during the fermentation of Fen liquor was monitored by derivatization followed by GC and GC-MS, together with that of pH measured using a pH meter and total acidity determined by acid-base neutralization titration. The results showed that total acidity of fermented grains generally displayed a rapid upward trend in the fermentation process except for a slight decline during days 9－11. pH of fermented grains was decreased to around 3.3 and total acidity was increased by 25 degrees after the fermentation. Among the identified organic acids in fermented grains, lactic acid showed the highest content and was dominant, followed by acetic acid, and both of them revealed a tendency to generally ascend in the whole fermentation process and their contents were over 10 times higher than that of acetic acid of the same time points at the late fermentation stage. The contents of the same organic acids in fermented grains and finished liquor were different. Based on this study, we posed a theoretical hypothesis that large-batch fermentation period in summer should be approximately 9 days and the number of fermentation batches should be increased, which is conducive to solving the spoilage problem and shortening fermentation period.

Key words: fermented grains, organic acid, derivatization, gas chromatography, gas chromatography-mass spectrometry, total acidity