When deciding whether to buy black tea or green tea or selecting the particular brand to purchase, there are many variables that can affect the quality of the product you choose. Depending on how the tea leaves are grown, manufactured or brewed, the end result you drink in your tea cup can vary greatly. Caffeine and polyphenols are sensitive to a variety of factors, and knowing these can help you choose what tea is right for you.
Oxidation
The most immediate effect on the polyphenol and caffeine content of tea leaves is oxidation. According to an article published in "The Leaf: Tea & Tao Magazine" by Robert J. Heiss, it is by oxidating and fermenting green tea leaves that black tea is created -- a process that results in the loss of the majority of the polyphenol antioxidants present in the leaves. Tannins and caffeine are increased, and the taste is intensified. Oxidation does not stop there, however. When exposed to air, dried tea leaves continue to oxidize, and factors that increase oxidation are increased exposure to air, the size of the leaves, and the age of the leaves. Tea bags tend to oxidize and degrade more than loose-leaf tea, and when pouring infused tea, pouring it into a cup from a greater height also increases the oxidation and affects the taste.
Origin
The balance of chemistry in your tea is affected by the country in which the leaves are grown and the environment they are exposed to. In a study published in "The Journal of Agricultural and Food Chemistry" in 2001, researchers from the Unilever Research Colworth in the U.K. compared polyphenol and caffeine content of different varieties of green and black tea from different countries. Green tea from Indonesia, Southern India, Bangladesh and Argentina had the highest polyphenol content, while Chinese and Indonesian green tea had the highest caffeine content. Black tea from Assam, Africa, and Darjeeling had the highest polyphenol content, and black tea from Assam, Africa, and Vietnam had the most caffeine.
Temperature
When making extracts of green tea and black tea, the heat of the water you use to infuse the leaves affects the balance of caffeine and polyphenols. In a study published in the journal "Food Science and Technology International" in 2010, researchers from the Iranian Academic Center for Education studied the results from using different methods of preparation on Iranian tea leaves. Hotter temperatures resulted caused degradation and a reduced content of both polyphenols and caffeine present in the tea leaves. Researchers recommended using water no hotter than 80 degrees Celsius to infuse tea to prevent the lose of active compounds.
Tea Bags
Tea bags contain what is known as "dust tea," which is highly refined or ground tea leaves. While some tea connoisseurs may reject the tea bag, infusing tea from tea bags provides increased amounts of active principles in the extract. According to research published in "Food Research International" in 1996, scientists from the Canadian Institute of Food Science and Technology studied the differences between tea bags and loose-leaf tea. When comparing the active principles extracted from three brands of tea bags and three brands of loose tea, they found the tea bags provided approximately twice the amount of methylxanthines, including caffeine and theobromine. More research is still needed to confirm whether tea bags or loose leaf tea provide better polyphenol antioxidants.
References
- The Leaf: Tea & Tao Magazine: Oxidation & Fermentation in Tea Manufacture
- The Journal of Agricultural and Food Chemistry: Factors Affecting the Caffeine and Polyphenol Contents of Black and Green Tea Infusions
- Food Science and Technology International: Extraction of Antioxidants and Caffeine From Green Tea (Camelia Sinensis) Leaves
- Food Research International: Tea Preparation and Its Influence on Methylxanthine Concentration
- Drugs.com: Green Tea
Member Comments