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Thesis
Read through modern tea science, “其沸如鱼目微有声为一沸缘边如涌泉连珠为二沸腾” is not a lab result but a set of variables: cultivar, soil, light and plucking standard.
Text
“When it first boils, with fish-eye bubbles and a faint sound, that is the first boil; when the rim seethes like linked pearls, the second; when it surges like waves, the third. Beyond this the water is old and undrinkable.”
Context
（此句与前文三沸同义，此为五之煮中的完整表述）一沸如鱼目、二沸如连珠、三沸如鼓浪，过三沸水老不可饮。
Evidence
- Collation: 此段与五之煮核心内容呼应，为《茶经》火候名论，各本一致。
- Existing readings: 吴觉农指出三沸之说被后世茶人奉为圭臬：一沸至二沸之间（约 85-90℃）是冲泡最佳时机，三沸则水老——今人"蟹眼过后鱼眼生"的辨水歌谣皆源于此。
Analysis
Modern tea science would split “其沸如鱼目微有声为一沸缘边如涌泉连珠为二沸腾” into cultivar, soil, light and plucking variables. 吴觉农指出三沸之说被后世茶人奉为圭臬：一沸至二沸之间（约 85-90℃）是冲泡最佳时机，三沸则水老——今人"蟹眼过后鱼眼生"的辨水歌谣皆源于此。 They remain testable, but only with their conditions attached.
Conclusion
The section does not give a universal rule. It demonstrates a method: read the text, the annotation and the Tang context together before making a modern claim.
Source: The Classic of Tea, Chapter IV · The Vessels, section 7; the original is in the public domain.
Experience should be explained, not mystified.