Chlorophyll a and b: The Two Pigments
All land plants contain two main forms of chlorophyll: chlorophyll a (C₅₅H₇₂MgN₄O₅) and chlorophyll b (C₅₅H₇₀MgN₄O₆). Chlorophyll a absorbs light primarily in the red (665 nm) and blue-violet (430 nm) parts of the spectrum, reflecting green light — which is why leaves appear green. Chlorophyll b absorbs slightly different wavelengths, broadening the light-capture range of the plant.
In a typical unshaded green tea leaf, chlorophyll a and b together constitute approximately 0.2–0.5% of dry weight. In shade-grown gyokuro and matcha-grade tencha, this can rise to 0.8–1.5% of dry weight — a three-fold increase that is clearly visible in the dramatically deeper green of shaded leaves and their processed products.
🧠 Expert Tip: Visual Quality Check
High-quality matcha should be a vivid, almost luminous green. A dull, khaki, or yellow-green colour indicates poor shading, old stock, or inadequate storage. Freshly ground, properly shaded matcha degrades visibly within weeks of opening if exposed to light and air — keep it sealed and refrigerated.
How Shading Increases Chlorophyll
When light levels drop, tea plants respond by upregulating chlorophyll synthesis to maximise the efficiency of available light for photosynthesis. This is a universal plant adaptation — the same process explains why shade-loving forest plants like ferns have such deep-green leaves despite receiving little direct sunlight.
In gyokuro and matcha production, this is deliberately exploited. The plants are covered with shading nets (typically reed screens or synthetic black fabric) for 20–30 days before harvest, reducing light to 10–20% of ambient levels. The chlorophyll increase is accompanied by a parallel increase in theanine and a decrease in catechins — the latter because sunlight normally drives catechin biosynthesis, which slows in shade conditions. This biochemical shift is precisely what gives shaded teas their characteristic umami-forward sweetness.
Kill Green: Preserving Chlorophyll Through Heat
In the processing of green tea, the "kill green" (shaqing in Mandarin, hi-ire in Japanese) step is the decisive moment for chlorophyll preservation. This process applies brief, intense heat — pan-firing at 250–280°C in Chinese production, steaming at 100°C for 30–60 seconds in Japanese production — to denature the enzyme polyphenol oxidase. Without this enzyme, the cellular machinery for chlorophyll degradation is disabled.
The difference between pan-fired and steamed green teas partly manifests in their chlorophyll content. Steaming, being briefer and involving moist heat, preserves slightly more chlorophyll (explaining the brighter blue-green of sencha and gyokuro compared to the more yellow-green of Longjing, which is pan-fired). However, steaming also preserves more grassy, seaweed-like volatile compounds that interact with chlorophyll-derived aromas.
🧠 Expert Tip: Brewing Chemistry
Green tea brewed at higher temperatures (90°C+) accelerates chlorophyll degradation during brewing — turning the liquor slightly yellowish. Brewing at 70–80°C preserves chlorophyll in solution, contributing to the vivid green colour of a properly brewed sencha. Never use boiling water for high-grade green teas.
Chlorophyll Degradation: The Science of Yellow and Brown Tea
| Chlorophyll Form | Colour | Condition | Process |
|---|---|---|---|
| Chlorophyll a | Blue-green | Fresh leaf, well-processed green tea | Intact |
| Chlorophyll b | Yellow-green | Fresh leaf, shade-grown teas | Intact |
| Phaeophytin a | Olive-brown | Poorly processed or aged green tea | Mg²⁺ replaced by 2H⁺ (acid/heat) |
| Phaeophytin b | Olive-yellow | Aged white teas, improperly stored | Mg²⁺ replaced by 2H⁺ |
| Pyrophaeophytin | Brown-grey | Severely degraded, stale tea | Esterase cleavage + demetallation |
Chlorophyll degrades through two main pathways: (1) Phaeophytisation — replacement of the central magnesium atom by hydrogen ions, triggered by acid, heat, or enzyme activity; and (2) Oxidative bleaching — destruction of the porphyrin ring system by reactive oxygen species. Both pathways produce progressively less green and more brown-yellow pigments. The resulting phaeophytins are entirely responsible for the yellow-brown discolouration of stale green tea. If your green tea brews a dull yellow rather than pale green, phaeophytisation has already occurred — the tea is no longer fresh.
Chlorophyll and Taste
Chlorophyll itself has a mild, slightly bitter, earthy taste at the concentrations found in tea. At higher concentrations — as in matcha — it contributes noticeably to the characteristic grassy, marine, slightly bitter base note underneath the umami sweetness. In powdered form, chlorophyll also coats the palate and provides a gentle physical thickness to the mouthfeel of whisked matcha that brewed leaf teas cannot replicate.
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