A 2025 Study Finds Rainy-Day Picking Cuts Wuyi Rock Tea Aroma

A 2025 chemistry study of Wuyi rock tea¹ found that leaf harvested on a rainy day carries 40 to 74 percent less of its key floral and fruity aroma compounds than the same cultivar picked from the same plantation on a sunny day.

What the study measured

The work was done on the Shuixian cultivar at a single Wuyi plantation, which removes the usual confounders of soil and varietal. The researchers took four samples from sunny days (May 8 and 17, 2022) and four from rainy days (May 10 and 14), then ran headspace solid-phase microextraction gas chromatography-mass spectrometry on each. In plain terms: they vaporized the volatile compounds from each tea and counted them, molecule by molecule. They calculated odor activity values, which weight each compound by how strongly the human nose registers it, and they seated a trained 25-member sensory panel to describe the cups.

The counts were not close. Total volatiles came to 7,038 micrograms per kilogram in the sunny teas and 4,162 in the rainy, a drop of 41 percent across 132 identified compounds. The named aroma molecules fell hardest. Phenylethyl alcohol, which carries a rose note, dropped from 511 to 131 micrograms per kilogram, a 74 percent reduction. (E)-nerolidol, fruity and floral, halved, from 573 to 285. Beta-ionone, the violet compound, fell in odor activity value from 277 to 167, a 40 percent drop. In all, 13 compounds registered above the perception threshold. Only 7 cleared it in the rainy ones.

The panel confirmed what the instrument found. Sunny teas showed a stronger flowery aroma; rainy teas showed weaker floral notes and a sour character. Even the liquor color parted: golden yellow from the sunny leaf, orange-yellow from the rainy.

What rain does to the leaf

The authors place the likely cause at the raw-leaf stage. Aroma is stored as precursors, and enzymes convert those precursors into the volatile compounds we smell. That conversion needs two things the weather governs: the right leaf moisture and an active enzyme system. Sunny conditions supply both. The leaf holds an optimal water level, the enzymes run, and the precursors turn over into aroma across the making. Leaf picked in rain retains excess surface moisture, which the authors write may suppress the conversion of aroma precursors.

The authors state the consequence directly: the development of tea aroma quality is significantly influenced by the weather on the day of harvest, rather than being solely dictated by the processing steps that follow.

What processing builds

A second 2025 study, tracking 251 volatile compounds through every stage of Wuyi rock tea manufacture, shows exactly how much the making builds. Terpenoids rose sharply through the turn-over stages and peaked at the sixth tossing. Fifteen compounds appeared only during the enzymatic stages, from withering through the green-making shake, most of them floral or sweet in scent; another four emerged only in the later firing stages, adding fruit.