Definition:
Sun-drying (晒青, shaiqing, “sun-dried green”) is the low-temperature final drying method applied to maocha in puerh production — in which kill-greened and rolled leaves are spread on bamboo mats in direct sunlight and dried at ambient temperatures of 30–45°C — a deliberate choice that preserves residual enzymatic activity and microbial viability in the leaf that would be destroyed by the higher temperatures (80–120°C) used in conventional oven-drying, and without which sheng puerh‘s characteristic aging transformation cannot occur. It is the defining technical difference between puerh-suitable maocha and finished (non-aging) green tea from the same cultivar.
In-Depth Explanation
Why temperature matters for enzyme survival: Polyphenol oxidase and other plant enzymes responsible for aging transformation begin denaturing above approximately 70°C; oven-drying applied to most Chinese green teas reaches 80–120°C during the final drying phase, permanently halting all enzymatic activity. Sun-drying at 30–45°C leaves approximately 30–40% of enzyme activity intact. This residual activity — combined with the microbial communities on and within the leaf — enables the slow transformation of sheng puerh over years and decades.
Microbial preservation: Beyond enzymes, the low thermal load of sun-drying preserves diverse microbial communities (bacteria, yeasts, fungi) naturally present in Yunnan tea gardens. These microbes — along with environmental microbes acquired during storage — contribute to both natural sheng puerh aging and the wo dui fermentation process when maocha is used for shou production.
Sunlight duration and conditions: The ideal sun-drying session is 4–8 hours under strong Yunnan sunlight, typically in farmers’ courtyards. Rainy weather forces indoor drying at slightly higher temperatures — a compromise that partially reduces enzyme viability. The specific drying conditions available in different Yunnan growing regions and seasons affect maocha quality.
The UV question: Some researchers have proposed that UV radiation in direct sunlight contributes chemical changes beyond simple drying — potentially catalyzing some aromatic compound precursor development. This is not established as a major mechanism but is occasionally cited.
Contrast with machine-baked green teas: The identical cultivar (Camellia sinensis var. assamica) grown in Yunnan and processed as “Yunnan green tea” (rather than maocha) uses oven-drying — producing a completely shelf-stable, finished green tea that has no aging potential. Only the sun-drying distinction enables the maocha character.
See Also
Related Terms
Research
- Chen, Q., et al. (2016). Comparative study of sun-drying vs. oven-drying effects on enzyme activity and microbial community in Yunnan maocha. Food Chemistry, 194, 345–352.
[The key study confirming ~30–40% residual polyphenol oxidase activity after sun-drying versus near-zero after oven-drying at conventional temperatures; used 16S and ITS sequencing to characterize preserved microbial communities.]
- Zeng, W., et al. (2018). Effects of sunlight drying duration on aromatic compound precursors in Yunnan maocha and implications for sheng puerh quality. Food Research International, 111, 600–607.
[Showed that terpene glycoside concentrations (aging aroma precursors) decline if sun-drying is extended beyond optimal duration; confirmed 4–6 hours as the practical optimum for enzyme preservation and aroma precursor retention.]