Influence Of Different Types Of Second Distillation On The Quality And Safety Index Of Chinese Liquors

Chinese liquor is a traditional alcoholic beverage in China. The distillation of Chinese liquor was usually performed by first-distillation using a special distill, which is called zengtong. While liquid pot still distillation was widely used in other spirits all over the world with second distillation or multiple distillation. Nowadays, little study on the influence of second distillation on the quality and safety index of Chinese liquor was well defined. In this study, first-distilled Chinese raw liquor was second-distilled through three types of second distillation, pot still distillation, atmospheric distillation, and vacuum distillation. Influence of different types of second distillation on the quality and safety index of Chinese liquors was investigated.The details are as follows:(1) Results showed that the distillation efficiency of pot still distillation was the highest, followed by atmospheric distillation and vacuum distillation. By the sensory preference ranking coupled with Friedman test and Page test(α=0.05), there existed significant difference in the quality of first-distilled strong aroma type raw liquor and three second-distilled liquors with a descending order of vacuum-distilled liquor, pot-distilled liquor, atmospheric-distilled liquor, and first-distilled strong aroma type raw liquor, sorted by preference. Second distillation effectively removed the off-flavor compounds(such as 4-methylphenol et al.) in the strong aroma type raw liquor. The double-distilled liquors showed substantial declines in total acids and various percentage declines in total esters compared with strong aroma type raw liquor, but still mantained the main style of strong aroma type liquor. Similar study showed that second distillation was suitable for the application of strong aroma type raw liquor and Chixiang aroma base liquor, while not so suitable for light aroma type raw liquor. Soy sauce aroma type raw liquor preferred atmospheric distillation rather than vacuum distillation.(2) Appropriate separation of head and tail could produce second-distilled liquor which EC concentration was much lower than that of raw liquor. EC was enriched in tail and stillage. The relative removal efficiency of pot still distillation was the highest(92.76%), followed by vacuum distillation(89.55%) and atmospheric distillation(81.46%). The EC concentration of slow-pot-distilled liquor was a little lower than that of fast-pot-distilled liquor, while there was no significant difference of the removal of EC through fast and slow pot still distillation. Removal of EC was effective in second distillation of first-distilled raw liquors with EC concentrations from 233.33 μg?L-1 to 1162.94 μg?L-1, and the relative removal efficiency of EC was between 89.91% and 92.76%. The sum weight of EC in head,heart, tail, and stillage increased 27.24~229.98% than the raw liquor. EC was newly formed during distillation.(3) The EC concentration decreased, then kept steady before gradually increasing with the reduction of alcoholic content during pot still distillation of first-distilled Chinese raw liquor. During the early stage of pot still distillation, EC might mainly come from the conversion of volitale cyanide, while in the late stage, it might come from the conversion of cyanide and other precursors. Pre-heating of raw liquor before pot still distillation effectively avoided the formation of EC from cyanide in the early stage of distillation. EC was enriched in tails which alcohol content was below 60%vol. Second distillation with appropriate separation of head and tail effectively reduced the EC concentration of Chinese liquor.(4) A second-order kinetics for the consumption of cyanide were found during the storage of newly second-distilled liquors. Decreased cyanide and increased EC indicated a good linear fit. Cyanide might be the significant precursor of EC during the storage of pot-distilled liquors. And high temperature and light distributed the formation of EC. Little relationship was found between decreased urea and increased EC during the storage after pot still distillation. After storage of one month, the EC concentration increased, but kept in a lower level than that in the first-distilled raw liquor. Pot still distillation effectively removed the EC in Chinese liquor, and low temperature, dark environment, and control of the initial cyanide content should be advised on the storage of post-distilled liquors to avoid EC formation.