# Effect of Fermentation Humidity on Quality of Congou Black Tea
###### Abstract  
This study investigated the effect of different fermentation humidities (55%, 65%, 75%, 85% and 95%) on congou black tea quality and bioactivity. Fermentation humidity mainly affected the tea's appearance, aroma and taste quality. The tea fermented at low humidity (75% or below) showed a decrease in tightness, evenness and moistening degree, as well as a heavy grassy and greenish scent, plus a green, astringent and bitter taste. The tea fermented at a high humidity (85% or above) presented a sweet and pure aroma, as well as a mellow taste, plus an increase of sweetness and umami. With increasing fermentation humidity, the tea exhibited a drop in the content of flavones, tea polyphenols, catechching (EGCG, ECG) and theaflavins (TF, TF-3-G), contrasted by a rise in the content of soluble sugars, thearubigins and theabrownins, contributing to the development of a sweet and mellow taste. Additionally, the tea showed a gradual increase in the total amount of volatile compounds and in the content of alcohols, alkanes, alkenes, aldehydes, ketones and acids. Moreover, the tea fermented at a low humidity had stronger antioxidant activity against 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) and a higher inhibiting capability on the activities of \(\alpha\)-amylase and \(\alpha\)-glucosidase. Overall results indicated the desirable fermentation humidity of congou black tea should be 85% or above. congou black tea; fermentation; humidity; quality; bioactivity +
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while increasing its umami [6]. [PERSON] et al. found that for Yunnan congou black tea, 3 h of fermentation time favored the preservation of simple catechins, the conversion of bitter and astringent substances, the formation of soluble sugars and the accumulation of aroma compounds [7]. [PERSON] et al. illustrated that fermentation temperature (25 \({}^{\circ}\)C to 30 \({}^{\circ}\)C) and fermentation time (60 to 90 min) were the crucial conditions affecting the conversion rate of phenolic compounds and fermentation direction. The brightness of tea liquid decreased with the increase of fermentation time, and fermentation at appropriate low temperatures contributed to the retention of polyphenol oxidase activity and the generation of good liquid color [8]. Fermentation humidity generally refers to the relative humidity in the environment during tea fermentation, i.e., the degree of water vapor in the wet air apart from saturation. Moisture is a direct participant and an essential solvent medium for the chemical reactions occurring in the fermentation of black tea. Changes in the relative humidity of the fermentation environment can affect the evaporation of water from the fermented leaves, thus changing their moisture content and affecting the chemical changes plus the type and quantity of products formed in the fermentation process [9]. At present, except for the limited research on the fermentation humidity gradient, few systematic studies have been devoted to black tea fermentation humidity at home and abroad [10]. In actual tea production, the fermentation humidity is usually determined based on experience, lacking a scientific and theoretical basis. Black tea can be divided into two categories based on their shape: congou black tea and broken black tea. The difference between the two in process is mainly determined by the rolling and rolling-cutting methods, and the resulting changes during fermentation. After withering, congou black tea is rolled by a rolling machine and the leaves are in the form of strips, while broken black tea is rolled and cut by a rolling-cutting machine after withering and the leaves are in the form of granules.