Study Of The Skin Contact Before Fermentation And Bitterness Of Guankou Dry White Wine

‘Guankou grape’is the characteristic variety of of Jianshi country in Hubei province.It is very important for‘Guankou grape’to develop the potential of further processing.There were a lot of problems in the process of‘Guankou dry white wine’,such as low juice yield,faste oxidation and browning,high bitterness intensity.In order to solve these difficulties,this study is mainly cover three aspects,Firstly,three major white grape varieties（‘Guankou grape’,Riesling,Chardonnay）were used for making dry white wines with clarified juice technology.Secondly,different skin contact times（0,12,24,48,120 h）and different concentrations of pectinase were choosen in the process of‘Guankou dry white wine’.The changes of phyto-chemical indexes,polyphenols contents,mono-phenols,animino acids,aroma compounds were determined of all the white wines.Meanwhile,sensory evaluation and quantitative descriptive analysis（QDA）were used for the wines sensory and aroma indexes to evaluate the quality of resulting wines.Additionally,the correlation analysis was used for selecting the main indexes for evaluating the bitterness and quality of wines,which could be applied to provide a certain theoretical reference on optimum processing of‘Guankou grape’.The main conclusions were as follows:（1）‘Guankou dry white wine’has a lower total phenol,total flavonoids,total flavanols than Riesling white wine,but higher than Chardonnay.The bitterness amino acid and mono-phenols of‘Guankou white wines’were higher than Riesling and Chardonnay white wines,but the non-bitterness amino acids and free aroma compounds were lower than Chardonnay,the bound aroma compounds were lower than Riesling white wines.The seneory score of wines from high to low was:Riesling>Guankou>Chardonnay,Riesling white wines was in the first place on aroma quality,pure taste,taste concentration,persistence,the overall balance,color and taste persistence.Thus,Guankou white wine was outstanding on the aroma characteristic of T Muscat,floral and tropical fruit.（2）As the extension of skin contact time,the titratable acid,reducing sugar,bitterness amino acids,free aroma composition of“Guankou white wines”were consistently reduced,the pH value,volatile acid,alcohol degree and SO₂ content increased,total phenol,total flavonoids,total flavanols,mono-phenols,bitterness amino acids,total amino acids and bound aroma components increased.Meanwhile,the Bitterness intensity of white wines increased gradually,the seneory score of wines from high to low was:Skin contat 12 h>48,24 h>0 h>120 h.Therefore,skin contact before fermentation can improve the quality of‘Guankou white wine’.As the extension of skin contact times,the aroma style of‘Guankou white wine’was transferred from flowers,tropical fruit and pineapple to citrus,green flavor,licorice,bitter almond and black coffee characteristics.（3）With the increase of pectinase usage,the titratable acid,free aroma compounds,volatile acid,total phenol,total flavonoids,total flavanols,mono-phenols,amino acids and bound aroma components of‘Guankou dry white wine’were increased.The seneory score of wines from high to low was:pectinase usage of 60 mg/L>20 mg/L>40 mg/L.With the increase of pectinase,the aroma of‘Guankou dry white wine’was more Complex,and the style of aroma wer transferred from roses and honey to tropical fruit,herbaceous,orange,black coffee characteristics.（2）In the study,the bitterness intensity was significantly positively related to total phenol,total flavanols,mono-phenol,caffeic acid,bitterness amino acid（p<0.05）,and significantly negative relates to proline content,non-bitterness amino acid,and total volatile compounds（p<0.05）,While the overall sensory evaluation had no significant correlation with the chemical indexes.