Green tea is derived from the leaves of the Camellia sinensis plant and has been consumed for thousands of years. It is valued for its health benefits as well as its refreshing flavor. But over time, the color of green tea can change from green to yellow. There are a few reasons why this color change occurs.
Oxidation
One of the main reasons green tea turns yellow is oxidation. Green tea leaves are not fermented like black tea leaves. The leaves are simply withered, steamed, and dried after harvesting. This minimal processing helps preserve the green color of the leaves as well as their catechin content. Catechins like epigallocatechin gallate (EGCG) are powerful antioxidants that provide many of green tea’s health benefits.
However, catechins can oxidize when exposed to oxygen, heat, and light. Oxidation causes the chlorophyll in the leaves to break down, making the leaves lose their green pigment. Over time, oxidized catechins react to form theaflavins and thearubigins. These compounds lead to the yellow or brownish color in aged green tea leaves.
Some oxidation occurs naturally during the processing and storage of green tea. But excess moisture, heat, UV radiation, and prolonged storage accelerates oxidation. Green tea that is store improperly or for too long is more likely to turn yellow.
Steeping Temperature
The temperature of the water used to brew green tea also affects its final color. Lower steeping temperatures around 170°F (75°C) help maintain the green color of the tea. This is because cooler water extracts less of the chlorophyll from the leaves.
In comparison, steeping green tea with boiling 212°F (100°C) water extracts more chlorophyll, leading to a yellow or brown appearance. The hotter water breaks down the green chlorophyll pigments faster.
Some Japanese green teas like sencha are meant to be brewed with cooler temperatures around 160-180°F (70-80°C). This helps preserve their greenish hue when served. Other types of green tea can withstand boiling water without changing color.
Water Quality
The mineral content of the water can also impact the brewed color of green tea. Hard water with high levels of minerals like calcium and magnesium tends to make the tea look yellow. This is because the minerals bind to and precipitate some of the tea compounds like catechins and chlorophyll.
Using filtered or bottled water that is low in minerals can help maintain the green color of brewed tea. Distilled water is best, as it contains no minerals that can alter the appearance of the tea infusion.
Green Tea Varieties
Different varieties and grades of green tea have varying tendencies to turn yellow. High-quality green teas made from younger leaf buds and shoots tend to retain their green color better. Examples include gyokuro and kabusecha from Japan.
In comparison, lower grades of green tea made from older leaves or broken leaves exhibit faster color change to yellow. The large surface area of broken leaves accelerates oxidation.
The cultivar also affects susceptibility to yellowing. Chinese green teas like longjing are less likely to turn yellow than Japanese green teas. However, most true green teas will eventually turn yellow over time.
Storage Conditions
How green tea is stored after processing plays a big role in its color stability. Green tea that is exposed to excess moisture, heat, UV light, or air will oxidize faster and develop a yellow tint.
Here are some tips for storing green tea to retain its green color:
- Keep in an airtight container away from light and heat
- Refrigerate or freeze for long-term storage
- Store loose leaf tea in opaque, sealed tins
- Press out air before sealing packaged tea
- Use tea within 1 year for best quality
Properly stored green tea can maintain its green color for longer. But eventually, oxidation will cause the leaves to slowly turn yellow over the years.
Freshness
The age and freshness of green tea also determines its susceptibility to yellowing. Fresher green tea made from the current harvest year will retain its green color longer.
In comparison, old green tea leaves from previous seasons undergo more oxidation during storage. This causes the aged leaves to turn yellow faster.
Drinking green tea within 1-2 years of production will provide the grassiest green color. The tea will gradually lose its fresh, green quality after this timeframe.
| Green Tea Age | Color |
|---|---|
| Current season | Vibrant green |
| 1 year old | Green with pale yellow tinge |
| 2+ years old | Yellow-green |
Yellow Tea
Some tea intentionally allowed to turn yellow is classified as “yellow tea.” This includes the famous Chinese junshan yinzhen tea.
Yellow tea is still made from Camellia sinensis leaves. But the leaves are permitted to slightly oxidize and mellow during processing. This results in a golden yellow liquor rather than green.
The oxidation process to create yellow tea is similar to green tea but slightly longer. The damp tea leaves are stacked to encourage fermentation before drying.
Buddhism and Color Symbolism
In Buddhist tradition, green symbolizes youthfulness and vitality while yellow represents wisdom and spiritual awakening. As green tea oxidizes over time and turns yellow, it’s said to acquire a richer, more enlightened character.
Some tea connoisseurs prize aged green teas for their mellower, earthier flavors compared to fresh green tea. Yellow-hued aged teas are said to promote inner peace and calmness.
Is All Yellow Tea Oxidized?
Not necessarily. While oxidation is the main cause of green tea turning yellow, there are other minor factors that can contribute to color change without fermentation occurring:
- Natural fading of chlorophyll over time
- Breakdown of carotenoid pigments
- Influence of pH and minerals on tea compounds
- Exposure to sulfur dioxide during processing
- Degradation of amino acids
These chemical changes in the leaves may lead to a yellowish tint even without full oxidation into yellow tea. But oxidation remains the primary driver of yellowing when green tea is stored.
Does Brewing Method Affect Color?
The brewing method can also influence the final color of prepared green tea. Steeping green tea leaves directly in hot water typically yields a yellowish brew. This is because the leaves continue to slowly oxidize and release pigments when submerged.
In comparison, brewing methods that expose the tea to hot water for a shorter duration help preserve the green color. Examples include infusing tea in a teapot and discarding the leaves, or steeping green tea just once in a small teacup.
Repeatedly steeping the same green tea leaves will turn the infusion progressively more yellow. This is why the Chinese gongfu tea ceremony uses multiple small steeps to extract the essence of green tea while keeping each brew vibrant green.
Does Decaffeination Cause Yellowing?
Most decaffeination processes utilize high heat, steam, or solvents that can degrade tea compounds and pigments. This accelerated aging effect may lead to faster yellowing in decaffeinated green teas.
However, high quality decaffeinated green tea that is processed gently using carbon dioxide or the Swiss water method can retain its green color well. The minimal processing helps protect against oxidation.
Conclusion
Green tea leaves naturally turn yellow over time due to oxidation. Improper storage conditions like excessive heat, light, and moisture can accelerate the oxidation process. Steeping green tea in hot water over 200°F also extracts more chlorophyll and leads to a yellow brew. While fresh green tea boasts a bright green infusion, aged green tea develops a mellower yellow tinge.
Enjoying green tea within 1-2 years helps maximize its vibrant green color and fresh flavor. But fans of oxidized yellow tea appreciate its golden hue and unique malty, earthy taste profile. Overall, the transition from green to yellow is a natural part of tea aging and is embraced by tea culture.
