Study on some technological factors affecting the processing of black tea from tea leaves Truoi in Phu Loc, Thua Thien Hue

Abstract

This study is the first to investigate the processing of black tea from traditionally harvested Truoi tea leaves. The harvested leaves were washed, drained, and stored in cold PE bags for further investigation and selection of suitable technological parameters. These parameters included the withering and drying stages based on indicators such as tannin content, polyphenol content, soluble content, moisture content, and sensory indicators of the black tea product. The Truoi tea leaves used in this study were the 3rd to 5th leaves. The withering process was carried out in a well-ventilated room at a temperature of 30 - 35°C, humidity of 73 - 75%, and a suitable withering time of 3 hours. The tea leaves had a moisture content of 65.83%, a tannin content of 21.05% dry matter (DM), a soluble content of 41% DM, and a polyphenol content of 16.67% DM. The rolling process was carried out for 30 minutes, achieving a cell rupture rate of 86.33% and a broken rate of 5.40%, which is in accordance with 10TCN 458:2001. The fermentation process was carried out at a temperature of 25 - 30°C, humidity of 85 - 90%, and a duration of 3 hours, resulting in a black tea product with the highest TF/TR ratio (1/14). Convection drying at a temperature of 90°C for 90 minutes was selected when the final black tea product had a moisture content below 5%, a polyphenol content of 14.44% DM, and a tannin content of 14.31% DM. The black tea product made from traditional Truoi tea leaves has a characteristic flavor, natural tea aroma, slightly bitter taste, and harmonious sweetness, which is typical of the product. The brewed black tea has a deep red-brown color with a golden rim.