Quality Analyses Of Curled-shaped Oolong Tea Based On Different Sensory Evaluation Methods

Organoleptic evaluation of oolong tea is one method that determines characteristics and quality levels of tea by human senses according to standard evaluation procedures. The evaluation of oolong tea is divided into two processes---valuation before infusion (called dry evaluation) and after infusion (called wet evaluation). The dry evaluation is dominated by strip and color of dry tea, combining with fragrance and extent of wholeness and cleanness, while the wet. evaluation focuses on taste and aroma of infused tea, combining with infusion color and infused leaves. Within the four factors of the wet evaluation process, flavor and aroma are the key and difficult factors for organoleptic evaluation of oolong tea, which determine quality level of oolong tea. According to regional and quality characteristics of tea,at present, organoleptic evaluation for oolong tea in China mainly has three methods, including organoleptic evaluation methods of Fujian oolong tea (referring to GB/T23776--2009The tea organoleptic evaluation methods), Guangdong DanChong tea (referring to Quality characteristics and evaluation technique points of Guangdong DanChong tea) and Taiwan oolong tea (referring to Chinese famous tea records---Identification of Taiwan Dongding tea).Using curled-shaped Fujian oolong tea and Taiwan oolong tea as raw materials for evaluation, this study discussed the correlation of PH value, color value with tea quality and the relationship between tea characteristics and temperature of two different brewing methods (Fujian brewing method with tea to water proportions of1:22and Taiwan brewing method with tea to water proportions of1:50) by studying change rules of temperature, bitter degree, hot feeling of oral cavity, color difference, taste chemistry, water extract content, PH value, conductivity and some physiological and biochemical indexes of tea infusion within0-36brewed minutes. The results were:1.Comparing two tea to water proportions of1:22and1:50, we discovered that to premium tea samples, the total score of sensory evaluation of1:50was higher than that of1:22, while to primary tea samples, the total score of sensory evaluation of1:22was a little higher than that of1:50.2.With regard to Fujian oolong tea samples, the pH value of infusion by Fujian brewing method was5.27～5.84, while the pH value of infusion by Taiwan brewing method was5.49～6.00, which indicated that the pH value of the latter was higher and was more closed to be neutral. As for Taiwan oolong tea, the pH value of infusion by Fujian brewing method was5.79～6.39, while the pH value of infusion by Taiwan brewing method was6.22～6.50. Therefore, it was obvious that the pH value of infusion by Taiwan brewing method was higher and more approached to be neutral than Fujian brewing method for both Fujian oolong tea and Taiwan oolong tea, and the pH value of infusion of Taiwan oolong tea was higher than that of Fujian oolong tea by both brewing methods. Fresh leaves of Fujian oolong tea were maturer than that of Taiwan oolong tea, so the more tender fresh leaves were, the higher the pH value of infusion was.3.The pH values of infusion of two tea to water proportions of1:22and1:50both become higher as brewing times increased.4.The conductivity of infusion of1:50was lower than that of infusion of1:22. By the brewing method with tea to water proportion of1:22, within three times brewings, the conductivity of infusion increased to the maximum in the second brewing and then decreased. However, by the brewing method with tea to water proportion of1:50, within twice brewings, the conductivity of infusion decreased with the maximum in the first brewing.5.The color difference analyses showed that for Fujian oolong tea L*value of infusion of1:50is higher than that of1:22, while for Taiwan oolong tea L*value of infusion of1:50was close to that of1:22.6.The taste chemistry of infusion determination showed that scores of body, umami and total score of taste of infusion of1:22were all higher than that of1:50. By the brewing method with tea to water proportion of1:22, within three times brewings (2min,3min,5min), the score of each factor of taste chemistry rose to the highest in the second brewing and then fell, while by the brewing method with tea to water proportion of1:50, within twice brewings (6min,6min), the score of each factor of taste chemistry fell with the highest in the first brewing.7.The extracted rate of infusion of1:22rose to the maximum in the second brewing (3min) and then dropped within three times brewings, while that of1:50declined with the highest in the first brewing (6min) within twice brewings. The extracted rate of infusion of1:50was higher than that of1:22in the first brewing, and the total extracted rates of infusion of1:50was lower than that of1:22.8.Medically,52℃is the optimum diet temperature for human’s oral cavity. By the brewing method with tea to water proportion of1:22, the infusion temperature of Fujian oolong tea could reach to about52℃when the first brewed (2min) and the second brewed (3min) was respectively left to stand for6min and the third brewed (5min) for4min through, while by the brewing method with tea to water proportion of1:50, the infusion temperature could reach to about52℃after letting the first brewed (6min) stand for4min.