温度和氧对啤酒老化的影响

研究了4℃、20℃和38℃三种温度条件下,不同溶解氧含量的啤酒其老化物质和香气成分的变化。贮存6个月后有关风味稳定性指标结果如下:贮存温度升高时5-羟甲基糠醛(5HMF)含量显著增加,从20℃到38℃增加了244%,氧含量对5HMF影响很小。TBN变化与5HMF相似,但不如5HMF敏感,从20℃到38℃只增加了5.3%。色度随着氧和贮存温度的增加而增加,38℃贮存的溶氧高的啤酒比4℃对照啤酒色度增加了3.18EBC。DPPH还原力随着贮存温度的升高而下降。贮存期间,对主要挥发性香气的跟踪分析表明,双乙酰在贮存过程持续增加,溶氧高的啤酒其含量更高,贮存2个月后,含量达到其风味阈值,导致啤酒产生“双乙酰”味。乙酸乙酯和乙酸异戊酯在贮存过程含量下降,38℃贮存6个月后,2种酯含量比4℃对照分别降低了18%和21%,溶氧高的啤酒降低程度更大,将会影响啤酒的香气。因此,减少成品啤酒的溶解氧含量,降低贮存温度,可以提高啤酒的抗老化能力。

Effects of Temperature and Oxygen on Bottled Beer Aging during Storage

Studies to investigate the effects of temperature and oxygen on flavor stability of Tsingtao during storage were described. Chemical data attributed to flavor stability was examined after storing for 6 months. A very high increase was found for 5-hydroxymethyl furfural (5-HMF) with higher storage temperature which increased a big margin from 20℃ to 38℃ by 244%, and it revealed no difference in 5-HMF content between beer with CO_2 and O_2. TBN acted the same as 5-HMF during beer aging, but it only increased by 5.3% from 20℃ to 38℃, the relative lower change showed that TBN is not as sensitive as 5-HMF to temperature increase during beer aging. The color increased with the increase in dissolved oxygen level and storage temperature, and the color of beer with O_2 stored at 38℃ increased by 3.18 EBC than control beer at 4℃. DPPH content decreased with the increase of storage temperature. The changes in the volatile fraction like diacetyl, esters and higher alcohols that may affect the aroma of Tsingtao during 6 months storage were also determined. The level of diacetyl increased continuous during 6 months aging, and the level in beer with O_2 was higher than with CO_2. After storing for 2 months, the content achieved its flavor threshold, therefore oxygen and temperature may cause “diacetyl” off-flavor in beer. Levels of ethyl acetate and isoamyl acetate decreased by 18% and 21% respectively after 6 months of storage at 38℃ compared to the control at 4℃, and decreased more in beer with O_2. Since levels of these two acetates in analyzed beer samples were close to their flavor threshold, the changes were expected to have an impact on the beer aroma. In conclusion, minimizing the dissolved oxygen content in beer and decreasing the storage temperature could improve the flavor stability of beer.