Chemical and Sensory Characteristics of Baiye No.1 (BY1H) Yellow Tea: Insights into Flavoring Mechanism and Quality Valuation

This study comprehensively evaluated Baiye No.1 (BY1H), a temperature-sensitive tea cultivar. Normally, it whitens in early spring and gradually regreens in autumn, accompanied by declining free amino acids and rising catechin and caffeine levels. We reevaluated the common belief that autumn tea is inferior. The feasibility of producing premium yellow tea from autumn-harvested BY1H was assessed, and the mechanisms underlying its quality formation were elucidated. The menhuang yellowing step played a central role. Driven by non-enzymatic thermal oxidation and hydrolysis, it reduced typical autumn defects by lowering phenolic and caffeine levels and increasing sweet-tasting free amino acids. Sensory evaluation, targeted metabolite profiling, and multivariate statistics were integrated to compare BY1H with four reference yellow teas (Ya’an Yellow Tea, Weishan Maojian, Yuan’an Luyuan Yellow Tea, and Pingyang Huangtang). BY1H yellow tea exhibited superior sensory attributes for its mellow-sweet taste and layered floral bouquet. Chemically, this profile was supported by a high water-extract yield, low levels of caffeine and ester-catechins, and abundant serine and phenylalanine. Together, these components contributed to its mellow-sweet taste. Gas Chromatography-Mass Spectrometry (GC-MS) analysis further identified 18 key volatiles, among which benzaldehyde, β-ionone, and methyl 2-(2-methylpropoxy)benzoate were the major contributors to the sweet-floral aroma. Partial Least-Squares Discriminant Analysis (PLS-DA) and Mantel tests confirmed BY1H’s unique chemical signature, clearly separating it from the other traditional yellow teas. These findings demonstrate that autumn BY1H leaves can be valorized through yellow tea processing, providing a scientific basis for cultivar innovation and sustainable utilization of seasonal tea resources.