<P> In addition to CO process extraction, tea may be also decaffeinated using a hot water treatment . Optimal conditions are met by controlling water temperature, extraction time, and ratio of leaf to water, where higher temperatures at or over 100 ° C, moderate extraction time of 3 minutes, and a 1: 20 water to leaf weight per volume ratio removed 83% caffeine content and preserved 95% of total catechins . Catechins, a type of flavanol, contribute to the flavor of the tea and also, interestingly, have been shown to increase suppression of mutagens that may lead to cancer . </P> <P> Both coffee and tea have tannins, which is responsible for the astringent taste, but tea has nearly three times smaller tannin content than coffee . Thus, decaffeination of tea requires more care to maintain tannin content than decaffeination of coffee in order to preserve this flavor . Preserving tannins is desirable not only because of their flavor, but also because they have been shown to have anticarcinogenic, antimutagenic, antioxidative, and antimicrobrial properties . Specifically, tannins accelerate blood clotting, reduce blood pressure, decrease the serum lipid level, produce liver necrosis, and modulate immunoresponses . </P> <P> Certain processes during normal production might help to decrease the caffeine content directly, or simply lower the rate at which it is released throughout each infusion . Several instances in China where this is evident is in many cooked pu - erh teas, as well as more heavily fired Wuyi Mountain oolongs; commonly referred to as' zhonghuo' (mid-fired) or' zuhuo' (high - fired). </P> <P> A generally accepted statistic is that a cup of normal black (often called red in China; as distinct from green) tea contains 40--50 mg of caffeine, roughly half the content of a cup of coffee . </P>

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