Tang dynasty writer Lu Yu's () "Cha Jing" ("The Classic of Tea") () is an early work on the subject. According to "Cha Jing," tea drinking was widespread. The book describes how tea plants were grown, the leaves processed, and tea prepared as a beverage. It also describes how tea was evaluated. The book also discusses where the best tea leaves were produced. Teas produced in this period were mainly tea bricks which were often used as currency, especially further from the center of the empire where coins lost their value. In this period, tea leaves were steamed, then pounded and shaped into cake or brick forms.