Guwahati: In a groundbreaking new study, scientists from Assam, one of the world’s premier tea-producing regions, have unveiled how the maturity of tea leaves dramatically impacts the quality of CTC black tea.
The study, published in the Journal of Food Measurement and Characterization, offers valuable insights into the optimal conditions for producing high-quality tea. Led by researchers from India’s Tocklai Tea Research Institute, the study examines five of Northeast India’s most popular tea cultivars: TV9, TV11, TV12, TV23, and S.3 A/3. CTC black tea—crush, tear, curl tea—gets its name from the method of processing used to create its signature flavor and appearance.
Primarily grown and consumed in India and other South Asian countries, CTC black tea is known for its strong, full-bodied flavor. Assam tea, in particular, is celebrated for its rich color and robust taste, making it a staple both within India and abroad. However, not all tea leaves are created equal, and a significant factor affecting tea quality is the maturity of the leaves at harvest.
The research team, led by Dr. Himangshu Deka, analyzed tea leaves harvested at three maturity stages: two-leaf and bud (2LB), three-leaf and bud (3LB), and four-leaf and bud (4LB). They assessed key quality indicators such as polyphenol, catechin, caffeine, and theanine levels in both the fresh leaves and the finished black tea. These compounds not only contribute to tea’s flavor but are also tied to its health benefits, including its antioxidant properties.
The study reveals that the younger, two-leaf and bud samples showed significantly higher levels of critical compounds, which are key to both taste and antioxidant activity. For instance, polyphenol levels, which enhance both the tea’s flavor and its health benefits, were highest in the youngest leaves (2LB) and declined as the leaves matured. This pattern was observed across all five tea cultivars tested. Catechins, a type of antioxidant present in green tea, followed a similar trend, decreasing as leaves aged. Catechins are highly valued in tea production, as they contribute to both the aroma and taste that many tea enthusiasts prefer.
The findings extended to sensory testing, where a panel of tasters evaluated teas made from leaves at each stage of maturity. The results were clear: teas made from the youngest leaves (2LB) scored highest, followed closely by those from 3LB leaves.
Across categories like briskness, strength, and overall quality, 2LB teas consistently outperformed others. According to Dr. Deka, “The tasters preferred the teas made from the younger leaves, which presented a brighter, more vivid infusion and a robust flavor profile.”
Another notable discovery was the impact of leaf maturity on the color of the brewed tea, which is a significant quality indicator. Younger leaves produced a rich, reddish-brown hue that is typically associated with high-quality Assam tea, while mature leaves resulted in a darker, less vibrant infusion. Colorimetric analysis supported this observation, showing significant differences in the L*, a*, and b* color values across maturity levels, which indicate lightness, redness, and yellowness, respectively.
“Recent research by the Tea Research Association to assess the impact of leaf maturity on the quality of processed CTC tea has shown that as leaves mature, the antioxidant activity decreases,” chairman of the Indian Tea Association Hemant Bangur said in a meeting recently.
“This opens up the scope for a quality benchmarking code and redefining quality standards. Conclusive research can provide consumers the knowledge to differentiate between various kinds of teas in terms of their qualitative and health-related advantages, as well as enable intervention by the introduction of a statutory scientific quality grading system with a one-leaf to five-leaves mark,” Bangur said.
These findings could reshape practices within Assam’s tea industry, which accounts for over half of India’s total CTC black tea production. Assam’s tea producers may benefit by focusing on harvesting younger leaves to enhance the final product’s taste, appearance, and antioxidant properties. As tea consumption continues to rise worldwide, optimizing leaf maturity could provide an edge in both domestic and international markets, reinforcing Assam’s reputation for producing some of the world’s finest black tea.
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