On the relative extraction rates of colour compounds and caffeine during brewing, an investigation of tea over time and temperature

Abstract

Various beliefs are common about the extraction of soluble compounds from leaf tea, suggesting that cold brewed tea or tea brewed for a shorter time than usual may contain a higher polyphenol-to-caffeine ratio, a selling point due to the potential health benefits of polyphenolic compounds. To test these beliefs, we investigated the effect of brewing time and temperature on the colour intensity and caffeine content of the extract of one type of black tea. Results showed that the extraction of the two components of interest had different half-lives, with an initial large variation of the ratio between them rapidly reaching a quite constant value. At different temperatures, a significantly different ratio between caffeine and colour compounds was observed. Although the difference in relative concentration was small, the range of brewing temperatures tested was only 20 Kelvin, so it seems possible to increase this difference. A difference in total extraction efficiency of both components together was noted too. To effectively change the ratio of the components using the extraction time would require using accurate times of less than 3 minutes and accurate temperatures unusual in a home environment.

Keywords

• tea
• caffeine
• polyphenols