An early credible record of tea drinking dates to the third century AD, in a medical text by Hua Tuo, who stated, "to drink bitter tu constantly makes one think better." Another possible early reference to tea is found in a letter written by the Qin Dynasty general Liu Kun. However, before the mid-8th century Tang dynasty, tea-drinking was primarily a southern Chinese practice. It became widely popular during the Tang Dynasty, when it was spread to Korea, Japan, and Vietnam. In India, tea has been drunk for medicinal purposes for a long but uncertain period, but apart from the Himalayan region it seems not to have been used as a beverage until the British introduced tea-drinking there much later.
Through the centuries, a variety of techniques for processing tea, and a number of different forms of tea, were developed. During the Tang dynasty, tea was steamed, then pounded and shaped into cake form, while in the Song dynasty, loose-leaf tea was developed and became popular.