Optimizing Extraction Parameters to Minimize Tannin Content in Uva Black Tea Infusions

Reina Shimizu; Hiroko Seki

Authors

Reina Shimizu School of Bioscience and Biotechnology, Tokyo University of Technology, Tokyo, 192-0982 Japan
Hiroko Seki Department of Local Produce and Food Sciences, Faculty of Life and Environmental Sciences, University of Yamanashi, Yamanashi, 400-8510 Japan

Keywords:

Uva black tea, Tannin, Polyphenol, Water hardness

Abstract

Uva black tea contains more tannins than other tea types, contributing to its rich color and astringency; however, excessive tannin levels may pose potential health risks, prompting efforts to reduce its content. Green tea studies suggest that lower temperatures, shorter infusion times, and metal ions suppress tannin leaching. Therefore, this study aimed to evaluate the impact of different extraction temperatures, time, water hardness, and calcium (Ca) and magnesium (Mg) ion content on tannin leaching levels in Uva black tea. Because tannins are high-molecular-weight polyphenolic compounds, measuring both total polyphenol and tannin concentrations was necessary to evaluate how water composition influences tannin removal. Polyphenol and tannin content were quantified spectrophotometrically. The results indicated that tannin concentration increased with higher extraction temperature and time. Hard water produced a darker color compared to soft water, though polyphenol and tannin levels showed no significant difference. Filtration with a coffee filter did not affect color, but centrifugation lightened the supernatant. Both treatments tended to reduce polyphenol and tannin concentrations. Ca and Mg are abundant in hard water. Therefore, in this study these ions were added individually and together to assess their effects on tannin concentration. The Ca-added group showed a color similar to hard water, while the Mg-only group resembled soft water. Varying Ca concentration did not raise pH, indicating that color change was not due to pH. These findings suggest that Ca contributes to color increase. To reduce tannins in black tea, using hard water to bind Ca with tannins and removing them through filtration is effective. Using a fine-mesh filter may further enhance the tannin reduction effect.

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