Experimental Study On White Tea 6CW-600 Withering Equipment And Discussion On Withering Online Feedback Parameters

White tea is favored by consumers for its appearance,apricot yellow color and fresh taste.Its processing process is:fresh leaves→withering→drying→hairy raw tea.Withering is the key process for the formation of white tea’s unique aroma,color and shape.In order to solve the problems that the existing white tea is difficult to wither in cloudy and rainy days,the labor cost of manual operation is high,the determination of leaf withering degree depends on the worker master,and the degree of intelligence is low.In this paper,the structure,working principle and performance of the newly developed 6CW-600 withering equipment integrating air controllable temperature and humidity control and automatic upper and lower leaves were analyzed,and the effects of different air velocity withering and different equipment withering on the quality of white tea were studied,which provides reference for the application of the new equipment,and discusses the online feedback parameters of white tea withering,so as to lay a foundation for the intelligent technology of white tea processing.The specific research results are as follows:1.Analysis of structure,working principle and performance of6CW-600 withering equipmentThe newly developed 6CW-600 withering equipment is composed of mesh belt tea leaf spreading withering machine,air supply system,water cooling auxiliary system and air controllable temperature and humidity control system.There are three ways to control temperature and humidity.The performance indexes such as air temperature,humidity and air velocity in the equipment were measured and analyzed.The results showed that the internal temperature stability of 6CW-600 withering equipment was higher than that of indoor and outdoor environment.At the same time,the temperature and humidity difference of each measuring point was less than that of withering room and withering tank,and the temperature and humidity distribution was more uniform.The equipment can effectively control the temperature and humidity of withering environment.The average air velocity of each test point in6CW-600 withering equipment was 0.2 m/s,and the difference was not significant.The coefficient of variation between each point was 5.43,which was less than that of withering trough（9.49）and withering room（31.32）.During the production of 6CW-600 withering equipment,the concentrations of PM_2.5and PM1₀in the environmental particles in the workshop were 39 ug/m³and 51.89 ug/m³respectively,which meet the relevant national requirements.During the production of 6CW-600withering equipment,the concentrations of PM_2.5and PM₁₀in the environmental particles in the workshop were significantly lower than those in the withering tank,resulting in less environmental pollution.When 6CW-600 withering equipment was running,the average noise of the workshop was 67.10 d B,which meets the national standard and was significantly lower than that of withering trough and withering room.6CW-600 withering equipment can effectively reduce the noise pollution of tea factory.The energy consumption of 6CW-600 withering equipment was only 60%of that of the withering tank and 87%of that of the withering room.It saved 40%energy compared with the withering tank and 13%energy compared with the withering room.The cost of6CW-600 withering equipment for producing dry tea per kilogram was0.51 yuan and 1.45 yuan lower than that of the withering trough and withering house respectively.2.Effects of different withering air velocity on the quality of white teaThe effects of different air velocities（0 m/s,0.5m/s and 1m/s）on the quality of white tea showed that under the same temperature and humidity of withering environment,the air velocity had a significant effect on the leaves phase and water content of withered leaves.With the increase of withering air velocity,the water loss of withered leaves accelerated,the lower the brightness L value of withered leaves,the higher the red and green a value,the lower the yellow and blue b value,and could promote the transformation of leaves color from gray to green.The sensory evaluation found that the white tea withered at 0.5 m/s air velocity had gray green color,fragrant aroma,mellow and refreshing taste,apricot yellow soup color,and the comprehensive score was higher than that of other white tea withered at air velocity.The catechin content of white tea withered at 0.5 m/s and 1 m/s air velocity was significantly lower than that of white tea withered at 0 m/s air velocity,while the total amount of sugars was significantly higher than 0 m/s,and the content of white theanine withered at 0.5 m/s air velocity was significantly higher than 0m/s and 1 m/s;There were significant differences in ketones and acids in the volatile gases of white tea withered at different air velocities.0 m/s air withered would promote the accumulation of acids,0 m/s air withered white tea would produce unpleasant special aroma such as caproic acid,naphthalene and n-valeric acid,while the substances with flower and fruit aroma such as nerol,linalool,methyl salicylate and jasmine in white tea withered at 0.5 m/s air velocity were significantly higher than those in other treatments.The air velocity of 0.5 m/s can be used as the reference air velocity of 6CW-600 withering equipment.3.Effects of different equipment to wither the quality of white teaThe study on the quality difference of white tea withered by6CW-600 withering equipment,withering trough and withering room showed that the overall temperature and relative humidity of 6CW-600withering equipment changed slightly,and the moisture content of tea at the end of withering was significantly higher than that of tea withered in withering trough.In the sensory quality of white tea withered by6CW-600 withering equipment,the soup color was light apricot yellow,the aroma is fragrant,the taste was mellowed and cooled,the leaves was soft,tender and even,and the comprehensive score was between withering trough and withering room.The contents of catechins and sugars in white tea withered by 6CW-600 withering equipment were significantly higher than those in withering tank and withering room,the total amount of amino acids was between withering tank and withering room,and the total amount of organic acids was significantly lower than that of white tea withered by other equipment.The white tea withered by6CW-600 withering equipment was mainly composed of nerolα-Ziluotong,phenylethanol,n-hexanol and benzyl alcohol were the main volatile characteristic components,which were significantly higher than that of white tea withered by other equipment.The comprehensive quality of white tea withered by 6CW-600 withering equipment had certain advantages,which could provide reference for the popularization and application of 6CW-600 withering equipment.4.Discussion on online feedback parameters of white tea witheringThe electric parameters of white tea withering in the second leaf were tested and analyzed.The correlation coefficients between five electric parameters and the regression equation of water content in the second leaf were more than 0.95,respectively:W=20.74+0.594Cs,W=16.508+5.992G,W=17.425+12.426G+4.795B-7.859Y,W=12.765+13.292B,W=15.008+5.457Y.The reliability and accuracy of the regression prediction model were good,which could be used as the online feedback parameters of white tea withering.The study on the dynamic change law of volatile gases in leaves making showed that five gases changed significantly,namely n-butane,acetic acid,butanol,acrolein and ethyl propionate,and the change range was more than 3 ppm.The results showed that the concentrations of these five gases showed a downward trend in the withering process of white tea,the content change difference reached a significant level every 12 hours,and decreased to about 50%at the end of withering.It can be seen that n-butane,acetic acid,butanol,ethyl propionate and acrolein can be used as feedback parameters for online judgment of white tea withering degree.