Abstract: This study aimed to explore the shaping of needle-shaped green tea at variable temperature and variable frequencies and to reveal the underlying mechanism for the purpose of providing the basis for automated shaping of needleshaped green tea. The effects of different variable-temperature variable-frequency shaping regimes on the quality of tea were compared, and the intrinsic mechanism underlying the shaping process was elucidated. The results showed that the tea samples produced by “high-high-middle” shaping scored highest (93 points) in sensory evaluation, having a fresh chestnutlike aroma, a fresh and mellow taste and a green and bright color. The ?a* values of the tea, tea infusion and tea leaves were 0.47, 5.07 and 3.33, respectively. The contents of tea polyphenols, amino acids, soluble sugar and chlorophyll in the tea were 28.65%, 2.64%, 3.78% and 3.68 mg/g. The moisture content showed no significant change during the early period of shaping at constant temperature and frequency, while the leaf temperature, caloricity and enthalpy increased quickly, reaching 64.4 ℃, 4.88 kJ/(kg/℃) and 173 kJ/kg at 3 min, respectively. During the middle period of shaping, the moisture content continuously decreased and the leaf temperature rose, accompanied by unchanged caloricity and a rapid decrease of enthalpy. During the late period of shaping, the moisture content fell rapidly, and the leaf temperature rose slowly, along with a simultaneous decrease in caloricity and enthalpy. At the end of shaping, the lowest enthalpy of 147 kJ/kg was observed. The entropy change reduced gradually but was always greater than zero, suggesting that the shaping process was irreversible. The average rate of water loss was 2.78%/min. The heat absorbed at different stages of the shaping process played different roles. Temperature rise mainly occurred at the early stage, both water loss and temperature rise mainly occurred at the middle stage, and the late stage was dominated by water loss, followed by temperature rise. To sum up, high temperature and high frequency for the early stage followed by proper reduction for the late stage helped the formation of green color and fresh and mellow taste in needle-shaped tea

Key words: needle-shaped green tea, variable t emperatures and variable frequencies, shaping, quality, mechanism