sayings. 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. During the Song dynasty, production and preparation of all tea changed. The tea included many loose-leaf styles (to preserve the delicate character favored by court society), and it is the origin of today's loose teas and the practice of brewed tea. A powdered form of tea also emerged. Steaming tea leaves was the primary process used for centuries in the preparation of tea. After the transition from compressed tea to the powdered form, the production of tea for trade and distribution changed once again. The Chinese learned to process tea in a different way in the mid-13th century. Tea leaves were roasted and then crumbled rather than steamed. By the Yuan and Ming dynasties, unfermented tea leaves were first pan-fried, then rolled and dried. This stops the oxidation process which turns the leaves dark and allows tea to remain green. In the 15th century, oolong tea, where the tea leaves were allowed to partially ferment before pan-frying, was developed. Western taste, however, preferred the fully oxidized black tea, and the leaves were allowed to ferment further. Yellow tea was an accidental discovery in the production of green tea during the Ming dynasty, when apparently sloppy practices allowed the leaves to turn yellow, which yielded a different flavour as a result. Tea production in China, historically, was a laborious process, conducted in distant and often poorly accessible regions. This led to the rise of many apocryphal stories and legends surrounding the harvesting process. For example, one story that has been told for many years is that of a village where monkeys pick tea. According to this legend, the villagers stand below the monkeys and taunt them. The monkeys, in turn, become angry, and grab handfuls of tea leaves and throw them at the