The aroma of Chinese rice wine Qu is one of the most important factors that influences the flavor of Chinese rice wine. To better understand the aroma of Qu, aroma compounds in four wheat Qus and two xiao Qus were identified by chromatography-olfactometry (GC-O) after solvent extraction followed by solvent-assisted flavor evaporation (SAFE). A total of 39 aroma compounds were characterized by GC-O. On the basis of aroma intensity, 1-hexanal, ethyl hexanoate, 1-octen-3-ol, and phenylacetaldehyde were found to be the most important aroma compounds in all six Qus. In addition, 3-methylbutanol and 2-phenylethanol also played an important role in the aroma of two xiao Qus. Headspace solid-phase microextraction (HS-SPME) was used for quantifying aroma compounds identified in the Qus. The method enabled limits of detection and quantification of <40.8 and <136.0 microg/L, respectively. Linearity and recovery were satisfied in all cases. Quantitative analysis revealed that volatiles of six Qus had a wide range of concentration. Principal component analysis applied to the data differentiated the six Qus well.

In order to understand the optimum time of using wheat Qu for Chinese rice wine brewing on the basis of the contents of volatile compounds, changes in volatile compounds of Chinese rice wine wheat Qu during fermentation and storage were studied by headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrum (GC-MS). It was shown that the concentrations of most groups of volatiles, including alcohols, aldehydes, aromatic compounds, phenols, sulphides, furans, and nitrogen-containing compounds, increased progressively from the first day to the fourth day of fermentation, and then decreased gradually. A minority group of volatile compounds such as acids and ketones peaked after one day of fermentation, esters increased slowly from the first day to the eighth day of fermentation. Lactones and esters rose slowly from the first day to the fifteenth day of fermentation respectively, and decreased afterwards, whereas the evolution of terpenes was somewhat erratic. These results suggested that changes in the concentrations of most groups of volatile compounds during fermentation and storage were uniform. This made it possible to determine the optimum level of fermentation and storage for Chinese rice wine wheat Qu on the basis of the contents of volatile compounds.

J. Inst. Brew. 116(3), 304-311, 2010The release of ferulic acid (FA) and the subsequent enzymatic decarboxylation to 4-vinylguaiacol (4-VG) were nearly ubiquitous during the production of Chinese rice wine. To evaluate the release of FA and the transformation to 4-VG, the levels of FA and 4-VG were determined by high performance liquid chromatography (HPLC) and gas chromatography-mass spectrum (GC-MS), respectively. During rice wine brewing, the concentrations of FA and 4-VG increased as fermentation time prolonged, with a rapid rise in days 1 to 5 of the main fermentation and followed by a slower rise from the 6th day post inoculation. FA and 4-VG levels in mashes, fermented by yeast with wheat Qu, were significantly higher than those in mashes fermented by yeast using commercial enzyme additions. The release of FA from rice by wheat Qu involves an enzymatic release mechanism. The levels of FA and 4-VG from rice flour by wheat Qu rose gradually during the first 24 h and then tended to stabilize. The capacity of yeasts to decarboxylate phenolic acids (Pof + phenotype) was absent in most rice wine brewing yeasts. These results suggest that the production of FA and 4-VG originated from materials in the wheat Qu rather than by the yeast during Chinese rice wine brewing and fermentation.