Definition:
Withering (萎凋, weidiao) is the controlled dehydration step applied to freshly harvested tea leaves — typically by spreading them in thin layers on bamboo or wire mesh racks in ventilated withering lofts for 12–24 hours (black tea), 72+ hours (white tea), or 4–8 hours (oolong) — reducing leaf moisture from approximately 75% to 55–70% water content, physically softening the leaf for rolling, and initiating the enzymatic and aromatic compound development that begins oxidation. It is skipped entirely for most green teas (which go directly from picking to kill-green)..
In-Depth Explanation
Physical effects: As leaf moisture decreases, cell turgor pressure drops and the leaf becomes pliable — “soft and silky” is the professional descriptor for properly withered leaves. This pliability is essential: if the leaf is too rigid when rolled, it shatters into dust rather than producing intact twisted or rolled shapes.
Chemical effects during withering:
- Amino acid release: As cells begin mild stress from dehydration, protein hydrolysis releases free amino acids, contributing to later aroma development.
- Caffeine concentration: As water is lost, the relative concentration of caffeine and other water-soluble compounds increases.
- Aroma compound precursor development: Enzymatic reactions during withering — particularly at the beginning when moisture is still high — generate terpene compounds (linalool, geraniol, phenethyl alcohol) that become the characteristic aromas developed in later processing.
- Early oxidation onset: The bruising from handling during withering and early cell membrane changes allow some PPO activity — this is intentional for oolong and black tea (where some pre-rolling oxidation is desirable) and must be avoided for green tea.
White tea wither: White tea’s long 72+ hour wither is essentially its entire processing — the extended dehydration with gentle air flow produces both the moisture reduction and the slow mild oxidation that gives white tea its character. Temperature, airflow, and humidity during the wither fundamentally determine white tea quality.
Oolong wither and tossing (yaoing): After initial withering, oolong leaves are periodically hand-tossed or tumbled in rotating drums — bruising the leaf edges deliberately to trigger controlled oxidation at cell-break sites. This characteristic oolong step is not part of black tea or white tea withering.
Controlled withering rooms: Modern large-scale tea factories use air-controlled withering rooms with temperature and humidity management. Traditional and craft producers use open-air bamboo tray withering in naturally ventilated facilities, adjusting tray thickness and timing by weather.
See Also
Related Terms
Research
- Owuor, P.O., & Orchard, J.E. (1994). The biochemical changes during withering of black tea and the implications for leaf quality. Food Chemistry, 50(3), 247–255.
[Comprehensive study documenting amino acid release, PPO activity changes, and chlorophyll degradation kinetics across a timed black tea wither; established 18-hour at 24°C as optimal for quality indicators.]
- Zeng, L., et al. (2016). Effect of withering on flavour compound generation in Chinese oolong tea with different cultivars. Journal of Agriculture and Food Chemistry, 64(38), 7120–7131.
[Confirmed that key oolong floral volatiles (linalool, geraniol) are generated primarily during the wither-and-bruise phase, not during rolling or oxidation.]