Longjing tea from bluish to deep green after steeping. Before infusion, higher quality Longjing teas have a very tight, flat shape and light green color. A study by Wang and Ruan (2009) found that one aspect of the perceived low quality of Longjing teas was a higher concentration of chlorophyll, producing a darker green color. The study revealed that free amino acids and theanine concentrations contribute positively to what is perceived as a good taste. Longjing tea was granted the status of Gong Cha, or imperial tea, in the Qing dynasty by the Kangxi Emperor. According to the legend, The Kangxi Emperor's
Wuyi tea technique for stopping the oxidation process of tea, pan-firing the leaves in a dry wok rather than steaming them as had been done previously. Songluo-style green tea became popular, and the new production method spread to other regions. In the 16th century, Wuyi tea makers invited monks from Songluo to teach their techniques to them. Eventually they discovered that by allowing the tea to partially oxidize before firing, they could produce a darker, fragrant type of tea which came to be known as oolong ("wulong", "black dragon") tea. European merchants began purchasing tea in Canton (Guangzhou) during the 17th century.