In 1391, the Hongwu emperor issued a decree that only loose tea would be accepted as a "tribute". As a result, tea production shifted from cake tea to loose-leaf tea and processing techniques advanced, giving rise to the more energy efficient methods of pan-firing and sun-drying, which were popular in Jiangnan and Fujian respectively. The last group to adopt loose-leaf tea were the literati, who were reluctant to abandon their refined culture of whisking tea until the invention of oolong tea. By the end of the 16th century, loose-leaf tea had entirely replaced the earlier tradition of cake and powdered tea.