A Colorimetric Method for Estimation of Fermented Degree in Black Tea Processing

This study was conducted to determine which color attribute change the more during fermentation in tea processing and if relationship between a tea pigment compound and the color index by fermentation level. Fermentation was performed after rolling. Hunter’s color value was measured either by using colorimeter or spectrum color meter. The liquor of finished tea was subjected to chemical analyses for total theaflavins, thearubigin, caffeine,catechin compounds. Hunter color b-value, yellowness, decreased during fermenting process while it was slightly increased at earlier stage. Hunter color a-value, redness, increased from minus value to plus during fermentation. The color b-value was higher than a-value in an earlier fermentation process. The difference Hunter value between b and a decreased gradually as fermentation time was increased, which values meet on a point at a certain fermentation time. After this time, color a-value was higher than the b-value. The result suggested that the color difference value between Hunter b and a can be applied on estimating fermented degree in black tea processing, with a relationship by the equation, ‘Fermentated Degree (%) = Hunter value b - a’. Total theaflavin increased until 30 min fermentation by 91.39 ± 4.80 mg% and then decreased by 36.79 ± 1.90 mg% at 180 min fermentation, while thearubigin increased until 120 min fermentation by 63.1 ± 1.92 mg% and then decreased by 30.8 ± 1.48 mg% at 180 min fermentation level. Caffeine and catechin compounds such as EGCg and ECg decreased as fermentation levels were high. These results was in agreement with the result that tea catechins changed to thearubigins through theaflavins. These results of chemical analysis also showed that the color difference data, Hunter value b-a, can be used to determine fermentation-stop point during black tea processing. If ICT technology is applied on automation of tea processing, the control of fermentation process can possibly be controlled and standardized by monitoring with automatic color difference meter.