Heterogeneity in Withering Conditions and Associated Changes in Key Nonvolatile Compounds in Black Tea (Camellia...

Black tea (Camellia sinensis) is a globally consumed beverage, in which the nonvolatile chemical matrix determines quality by shaping liquor color, taste, and mouthfeel. Withering regulates dehydration kinetics and biochemical conditioning, thereby priming leaves for downstream pigment and flavor development. Following PRISMA guidelines, this systematic review and meta-analysis quantified how withering, as an independent experimental variable, modifies major nonvolatile constituents in black tea. Eligible experimental studies published between 2000 and 2025 were recorded, and the effect sizes were computed as the natural log response ratio (lnRR) and pooled using random-effects (REML) models. Heterogeneity was quantified using Q, τ², and I². Nineteen studies met the inclusion criteria, mostly published within the last 5 years and concentrated in China. Across studies, withering altered catechins, amino acids (including theanine), tea pigments, alkaloids, and organic acids, with substantial between-study variability indicating strong context dependence. Conventional natural indoor withering tended toward net catechin depletion, broadly consistent with progressive oxidation and priming for pigment formation. Conversely, withering interventions, such as warm air, dynamic handling, light irradiation, and pulsed electric field, tended to show the largest deviations, though small study counts (k = 1-3) and extreme heterogeneity render these preliminary trends rather than reproducible method effects. These findings suggest withering may shape black tea chemistry rather than serving as a fixed dehydration step, although cultivar, endpoint moisture, dehydration kinetics, and sampling stage often influence outcomes as strongly as the nominal method. Interpretation remains limited by extreme heterogeneity and inconsistent reporting of intensity-defining variables; the review therefore proposes a standardized reporting checklist as a primary translational output for future syntheses.