Matcha Color as Quality Indicator
High-quality matcha measures CIELAB L* ≤52 and a* of −11 to −9 (green axis). Dull olive or yellow-green color (L* >58, a* >−7) indicates chlorophyll degradation to pheophytin from age, heat, or sun-grown leaves — a reliable quality proxy.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Ceremonial grade CIELAB L* (lightness) | ≤52 | L* | Lower = darker = higher chlorophyll; L*=0 is black, L*=100 is white |
| Ceremonial grade CIELAB a* (green axis) | −11 to −9 | a* | Negative a* = green; more negative = greener; positive a* = red |
| Low-quality matcha CIELAB L* range | 58–70 | L* | Visually yellow-green; low chlorophyll or high pheophytin |
| Chlorophyll → pheophytin conversion temperature | >60 | °C | Heat accelerates Mg loss from chlorophyll ring, producing olive-yellow pheophytin |
| Pheophytin color shift | Yellow-olive | vs. vivid green of intact chlorophyll; visible shift occurs with significant degradation | |
| UV exposure effect on matcha color | Significant fading within weeks | Chlorophyll photodegradation; packaging must block UV |
Color is the most immediate, accessible quality indicator for matcha — and one of the most reliable. The link between matcha color and quality is not aesthetic preference; it reflects the underlying chlorophyll chemistry that also correlates with L-theanine content and freshness.
Understanding CIELAB Color Space
The CIE Lab* (CIELAB) color model describes colors in three dimensions:
- *L (Lightness)**: 0 = pure black, 100 = pure white
- a* (Red-Green axis): Negative = green, Positive = red
- b* (Blue-Yellow axis): Negative = blue, Positive = yellow
High-quality matcha occupies a specific zone: L* 45–52, a* −11 to −9, b* approximately +5 to +15. Lower-quality matcha drifts toward higher L* (lighter), less negative a* (less green), and higher b* (more yellow).
Visual Assessment Without Instruments
Without a colorimeter, use these heuristics:
High quality: Deep, vibrant green — similar to spring grass or fresh peas. Should catch the light with a slight blue-green undertone. Under bright light, should appear almost luminously green.
Medium quality: Lighter, grassy green. Acceptable for culinary use; lacks the intensity of premium matcha.
Low quality or aged: Yellow-green, olive, or dull khaki. Indicates either low-grade leaf (sun-grown, older harvest) or degradation from heat, light, or moisture exposure. Not suitable for ceremonial preparation; usable in baking where other flavors dominate.
Pheophytin: The Chemistry of Dull Green
When chlorophyll ages or is exposed to heat (>60°C) or UV light, the central magnesium atom in the chlorophyll ring is replaced by hydrogen atoms. This creates pheophytin, a compound with an olive-yellow color. The conversion is irreversible — there is no way to restore green color once pheophytin has formed. This is why proper storage (cool, dark, airtight) is essential for maintaining matcha’s color and flavor.
Color and L-Theanine Correlation
Multiple studies have found a statistically significant correlation between CIELAB a* value (greenness) and L-theanine concentration in matcha. This makes intuitive sense: both chlorophyll and L-theanine accumulate under shade-growing conditions. A vivid green matcha is therefore also likely to have higher L-theanine — though this correlation is statistical, not perfect, and direct measurement remains the most reliable verification.