In China during the Tang Dynasty (618–907), tea leaves were steamed and formed into tea bricks for storage and trade. The tea was prepared by roasting and pulverizing the tea, and decocting the resulting tea powder in hot water, then adding salt. During the Song Dynasty (960–1279), the method of making powdered tea from steam-prepared dried tea leaves, and preparing the beverage by whipping the tea powder and hot water together in a bowl became popular.
There are also several harmful effects of green tea over-consumption that are possible. These include consuming tainted supplements marked as green tea extract, high caffeine consumption, consuming aluminum, and the effects of tea polyphenols on iron bioavailability. Green tea extracts should not be taken by patients suffering from renal failure, liver disease, heart conditions or major cardiovascular problems without supervision from a doctor. People sensitive to caffeine should be careful of their intake. Pregnant and breast-feeding women should drink no more than one or two cups per day, as some research shows that more caffeine than this amount may interfere with normal heart rhythms.
The South African Department of Trade and Industry issued final rules on 6 September 2013 that protects and restricts the use of the names "rooibos", "red bush", "rooibostee", "rooibos tea", "rooitee" and "rooibosch" in that country, so that the name cannot be used for things not derived from the Aspalathus linearis plant. It also provides guidance and restrictions for how products which include Rooibos, and in what measures, should use the name "rooibos" in their branding.
Shade grown: All matcha is made from shade-grown tea leaves—a labor-intensive process where tea bushes are protected from the sun and light is filtered to the bushes in a very controlled manor. Shading boosts the chlorophyll production in the plant, giving the leaves a rich green color. The lack of sun reduces the plant’s photosynthesis of the leaves, which in turn alters the naturally occurring levels of caffeine, flavanols, sugars, antioxidants, and theanine. By controlling the sun exposure, tea producers can significantly alter the chemical make-up and flavor of the final tea leaves.