# Effect of Fermentation Humidity on Quality of Congou Black Tea
## 3 Results and Discussion  
### Effects of Fermentation Humidity on Congou Black Tea Sensory Quality  
Due to different humidity levels during the fermentation process, the five treatments showed differences in the appearance of tea leaves at the end of fermentation (Figure 1). As the fermentation humidity rose, the greenness of the fermented leaves decreased and the redness and gloss rose. Under low fermentation humidity conditions (55%, 65%), the fermented leaves were greenish-yellow and darker, while under high fermentation humidity conditions (85%, 95%), the fermented leaves turned yellowish-red and brighter. Studies have shown that well-fermented black tea leaves will have a bright red color due to the sufficient decomposition of chlorophyll and the generation of thearubigins and theaflavins [13]. In addition, feeling the tea leaves with the hand at the end of fermentation revealed that as fermentation humidity rose, the fermented leaves' surface became progressively moister. Under low fermentation humidity conditions (55%, 65%), the fermented leaves were drier and had a distinctly prickly feel to the hand, and the trabs were slightly pudulous relative to the rolled tea leaves. However, under high fermentation humidity conditions (85%, 95%), the fermented leaves were moister and softer. This is probably due to the increased transpiration and water loss from the fermented leaves at lower relative humidity, resulting in a drier surface [14]. This result suggests that low humidity conditions are unfavorable to congou black tea fermentation. The sensory assessment results of congou black tea with different fermentation humidity treatments are shown in Table 1, where the tea's appearance, aroma, taste and infused leaf were all seen to be greatly impacted by fermentation humidity. As shown by the QDA results in Figure 2, as the fermentation humidity increased, the tightness of the dried tea trabs and the shape uniformity gradually improved, coupled with better moistness, agreeing with the change trend in the appearance of the fermented leaves after fermentation. Under high humidity conditions, both the surface and internal leaves in the fermentation baskets were at a similar humidity level, indicative of consistent chemical changes, and no issue of uneven fermentation. In low humidity conditions, the surface-fermented leaves in the fermentation basket lost water more rapidly, causing the fermented leaves to wrinkle, deform and feel prickly, leading to a reduction in the tightness and moistness of the tea leaves after drying. Unlike the surface-fermented leaves, the fermented leaves inside the fermentation basket evaporated water at a slower rate, leading to variations in the degree of deformation and chemical changes in the same basket, hence nonuniform fermentation and a decrease in the evenness of the tea sample. In terms of aroma quality, the tea leaves had a grassy scent for RH55, RH65 and RH75 treatments, with a green tea-like odor in the RH55 and RH65 treatments. Once the fermentation humidity rose to 85%, the grassy scent and miscellaneous odor disappeared and the aroma turned sweet and pure. During black tea fermentation, the content of leaf aldehydes, which present a greenish smell, gradually decreased, in contrast to the content increase of linalool and other aromatic compounds, which have a floral or sweet aroma, thus changing the aroma of the black tea from unpleasantly green to pleasantly sweet, floral or fruity [15]. This indicated that fermentationat low humidity is unfavorable to the formation of black tea's aroma quality. In terms of taste quality, black teas fermented at less than 75% humidity had a green, astringent and bitter taste, probably due to insufficient fermentation, thus preventing the full oxidation of the tea polyphenols and leading to their high content, especially the retention of the astringent ester-type catechins [16]. In contrast, black teas fermented at 85% humidity or more exhibited a mellow and sweet taste with obvious umami characteristics.