Original: Fujian, China
Steeping, brewing and serving
Steeping, or brewing, is the process of making tea from leaves and hot water, generally using 2 grams (0.071 oz) of tea per 100 millilitres (3.5 imp fl oz; 3.4 US fl oz) of water (H2O) or about 1 teaspoon of green tea per 150 ml cup. Steeping temperatures range from 61 °C (142 °F) to 87 °C (189 °F) and steeping times from 30 seconds to three minutes.
Generally, lower-quality green teas are steeped hotter and longer while higher-quality teas are steeped cooler and shorter, but usually multiple times (2–3 typically). Higher-quality teas like gyokuro use more tea leaves and are steeped multiple times for short durations. Steeping too hot or too long results in the release of excessive amounts of tannins, leading to a bitter, astringent brew, regardless of initial quality. The brew's taste is also affected by the steeping technique; two important ones are to warm the steeping container beforehand to prevent the tea from immediately cooling down, and to leave the tea leaf in the pot and gradually add more hot water during consumption.
Numerous claims have been made for the health benefits of green tea, but human clinical research has not found good evidence of benefit. In 2011, a panel of scientists published a report on the claims for health effects at the request of the European Commission: in general they found that the claims made for green tea were not supported by sufficient scientific evidence. Although green tea may enhance mental alertness due to its caffeine content, there is only weak, inconclusive evidence that regular consumption of green tea affects the risk of cancer or cardiovascular diseases, and there is no evidence that it benefits weight loss.
Although using green tea as a health supplement green tea is associated with a slight improvement in overall quality of life, it is also associated with some potential adverse effects. A 2020 review by the Cochrane Collaboration listed these as gastrointestinal disorders, higher levels of liver enzymes, and, more rarely, insomnia, raised blood pressure and skin reactions.