Optimizing dehydration ratio and rate during the withering process enhances aroma quality of oolong tea

Withering plays a pivotal role in shaping the flavor and aroma quality of the final product, and dehydration ratio (DR) and dehydration rate (DRt) are key parameters during withering. In this study, the DR and DRt during solar withering and indoor withering (ID1) of Oolong tea were investigated, and the GC-MS and sensory evaluation were employed to assess tea aroma. The result showed that the DR and DRt of solar withering (DR 10%, DRt 16.67%/h) were significantly higher than those in ID1 (DR 1.3%, DRt 2.08%/h). Headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis and sensory evaluation revealed that increasing DR and DRt significantly elevated the total volatile content in withered leaves and promoted the conversion of aldehydes to alcohols and esters. Further experimental groups verified that DRt was critical and highly related to the development of aroma compounds instead of the DR. Orthogonal Partial Least Squares-Discriminant Analysis (OPLS-DA) identified seven key aroma compounds, including linalool, nerolidol, and indole, which showed strong positive correlations with DRt. Additionally, the samples with higher DRt (SL and ID3 treatments) substantially enhanced floral-fruity terpenoids and esters while reducing grassy aldehydes to achieve the highest aroma scores, dominated by floral and honey notes. These findings provide new insights into optimizing indoor withering parameters under rainy conditions, offering a practical solution to overcome climate-dependent limitations in traditional oolong tea processing.