Optimization of Fermentation Time, Temperature, and Tea Bed Thickness in CFM to Enhance the Biological Composition of CTC Black Tea

Black tea, a globally cherished beverage, derives its distinct flavor, color, and health benefits from the complex fermentation process it undergoes during production. This study aims to optimize the fermentation process in continuous fermentation machines (CFM) to enhance the biological composition and overall quality of CTC (Crush, Tear, Curl) black tea. The focus is on critical quality indicators, including theaflavins (TFs), thearubigins (TRs), catechins, redness index, and yellowness index. Utilizing Response Surface Methodology (RSM), the study systematically investigated the effects of three variables: fermentation time (5–120 min), temperature (25–40 °C), and tea bed thickness (5–12 cm). The concentrations of TFs, TRs, and catechins were determined using high-performance liquid chromatography (HPLC), while the redness and yellowness indices were assessed using colorimetric methods. The research identified the optimal fermentation conditions as a temperature of 25 °C, a tea bed thickness of 11.937 cm, and a fermentation time of 65.629 min. Under these conditions, the tea exhibited significant improvements in TF and TR levels, along with optimal redness and yellowness indices, which are closely linked to the desired flavor, visual appeal, and potential health benefits of black tea. These findings offer valuable insights for tea manufacturers, providing a systematic approach to refining the fermentation process to produce higher-quality CTC black tea, thereby improving product consistency and competitiveness in the market.