You steep a tea bag in hot water, and clear liquid transforms into amber, brown, or deep mahogany. It happens so reliably that we rarely stop to ask: why does tea turn brown? The answer involves oxidation, chemical compounds, and the remarkable transformations that occur during tea processing.
The Short Answer
Tea turns brown primarily due to compounds called theaflavins and thearubigins. These are formed when polyphenols in tea leaves oxidize—a process that happens during tea processing and continues when you brew. The more oxidized the tea, the darker the color.
But this simple answer only scratches the surface. The science of tea color reveals fascinating chemistry and helps explain why different teas produce such varied hues.
Understanding Tea Processing and Oxidation
All true tea comes from the same plant: Camellia sinensis. What differentiates green tea from black tea isn’t the plant variety (though varieties exist) but rather how the leaves are processed after harvesting.
The Role of Oxidation
When tea leaves are damaged—rolled, crushed, or simply bruised—enzymes inside the cells contact polyphenols (antioxidant compounds) and oxygen. This triggers oxidation, a chemical reaction that transforms the leaf’s composition and color.
Think of it like an apple turning brown after you cut it. The same principle applies to tea leaves, just in a controlled way.
Tea Types by Oxidation Level
White tea (0-10% oxidation): Minimal processing, leaves are simply dried. Very light, pale yellow brew.
Green tea (0-10% oxidation): Heat is applied quickly to stop oxidation (steaming in Japanese style, pan-firing in Chinese style). Light green to yellow brew.
Oolong tea (10-80% oxidation): Partial oxidation creates a spectrum from light greenish to deep amber. This wide range explains oolong’s variety.
Black tea (80-100% oxidation): Fully oxidized before drying. Deep amber to dark brown brew.
Pu-erh tea (post-fermented): Undergoes microbial fermentation after oxidation. Can produce very dark, almost black brews.
The Chemistry Behind the Color
Starting Point: Catechins
Fresh tea leaves contain catechins—colorless polyphenolic compounds that act as antioxidants. The most abundant catechins in tea are:
- EGCG (epigallocatechin gallate)
- EGC (epigallocatechin)
- ECG (epicatechin gallate)
- EC (epicatechin)
These compounds are largely preserved in green tea, which is why green tea stays light-colored.
Transformation: Theaflavins
When catechins oxidize, pairs of them combine to form theaflavins—orange-red pigments that contribute to black tea’s bright, coppery appearance. Theaflavins also affect taste, adding astringency and briskness.
Black teas with high theaflavin content appear more golden and have that characteristic “bright” quality prized in Assam and Ceylon teas.
Further Oxidation: Thearubigins
As oxidation continues, theaflavins and remaining catechins transform into thearubigins—larger, more complex molecules that create deep brown and red colors. Thearubigins are less well-understood than theaflavins but constitute the majority of pigments in fully oxidized black tea.
These compounds contribute body and depth to tea’s flavor profile, though they’re less astringent than theaflavins.
Why Black Tea Is Brown, Not Black
Despite the name, properly brewed black tea is typically amber, copper, or mahogany—not black. The “black” refers to the dry leaf color after full oxidation. When brewed, the combination of theaflavins (orange-red) and thearubigins (brown-red) produces those warm amber tones.
Tea that brews truly dark brown or nearly black is usually over-steeped, extracting excessive tannins and pigments.
Factors That Affect Your Brew’s Color
Steeping Time
Longer steeping extracts more pigments (and tannins). This is why over-steeped tea looks darker and tastes more bitter—you’ve pulled out compounds that would otherwise remain in the leaves.
Recommended steeping times exist for good reason: they balance color, flavor, and astringency. A 3-minute black tea steep produces different color than a 5-minute steep.
Water Temperature
Hotter water extracts compounds faster. This is why black tea (steeped at boiling) darkens quickly, while green tea (steeped at 160-180°F) stays lighter even with similar steep times.
Using water too hot for delicate teas not only darkens the brew but also extracts bitter compounds and can scald the leaves.
Leaf Quality and Processing
Broken or crushed leaves (typical in tea bags) have more surface area and release pigments quickly. Whole leaves extract more slowly, producing lighter brews at equivalent steep times.
CTC (crush-tear-curl) processed black teas are designed for quick extraction and produce darker brews than orthodox whole-leaf teas.
Water Chemistry
Your water’s mineral content affects tea color. Hard water (high mineral content) can react with tea compounds to produce darker, sometimes muddier brews. Soft water typically produces brighter, cleaner color.
This is why the same tea can look different depending on where you brew it—London’s soft water vs. a hard-water region produces visibly different results.
Why Different Teas Have Different Colors
Green Tea: Pale Yellow to Light Green
Heat-treating leaves shortly after harvest deactivates the enzymes responsible for oxidation. Catechins remain intact (colorless), so the brew reflects chlorophyll (green) and other minor pigments rather than oxidation products.
Japanese green teas steamed longer tend toward greener brews; Chinese pan-fired greens lean more yellow.
White Tea: Pale Gold
Minimal processing means minimal oxidation—but some occurs naturally during drying. The result is very light brews with subtle yellow-gold coloring from trace oxidation.
Oolong Tea: Light Gold to Deep Amber
Oolong’s oxidation spectrum produces the widest color range of any tea category. Lightly oxidized Taiwanese oolongs can be pale and green-tinged. Heavily oxidized Wuyi oolongs approach black tea’s deep amber.
Black Tea: Amber to Mahogany
Full oxidation creates maximum theaflavins and thearubigins. Specific color varies by region and processing:
- Darjeeling: Light, bright copper
- Assam: Deep, reddish-brown
- Ceylon: Bright amber
- Yunnan: Golden-orange
Pu-erh Tea: Deep Brown to Black
Aged pu-erh undergoes microbial fermentation that creates unique compounds not found in other teas. Ripe (shou) pu-erh can produce ink-dark brews with earthy, complex flavors.
Common Questions About Tea Color
Is Darker Tea Stronger?
Not necessarily. Color indicates extraction level and oxidation style, not caffeine content. A strong green tea can have more caffeine than a mild black tea. Color tells you about compounds extracted, not “strength” in any universal sense.
Why Does My Tea Look Cloudy When Cold?
Tea can “cream” when cooled—theaflavins and thearubigins bond with caffeine to form visible particles. This happens more in strongly brewed black teas and doesn’t affect flavor. Cold brewing avoids this because less caffeine extracts at cold temperatures.
Why Does Adding Lemon Lighten Tea?
The citric acid in lemon changes the pH of your tea, altering how theaflavins and thearubigins absorb light. The pigments don’t disappear—they just appear lighter in acidic conditions. This also explains why some teas lighten when you add acidic fruits.
Does Milk Change Tea Color?
Milk proteins (casein) bind with tea tannins and pigments, producing the characteristic tan color of milk tea. This is a chemical interaction, not just dilution—the compounds change how they reflect light.
What Color Tells You About Your Brew
Learning to read tea color can improve your brewing:
Too light: Under-extracted. Try longer steeping, hotter water, or more tea.
Too dark: Over-extracted. Reduce steep time, lower temperature, or use less tea.
Muddy or dull: Water too hard, leaves too old, or over-steeped. Try filtered water and fresh tea.
Cloudy when hot: Usually indicates low-quality tea or excessive steeping.
The “right” color depends on the tea and your preferences—but knowing why color changes helps you achieve consistent, enjoyable results.
The Bottom Line
Tea turns brown because oxidation transforms colorless catechins into theaflavins (orange-red) and thearubigins (brown-red). The more oxidized the tea, the darker the brew. Processing methods, steeping parameters, and water chemistry all influence the final color in your cup.
Understanding this chemistry does more than satisfy curiosity—it helps you appreciate the craftsmanship in tea processing and gives you control over your brewing results. That amber liquid in your cup represents centuries of refined technique and remarkable chemical transformation, all from a simple leaf steeped in hot water.