esoteric foods and common household cuisine of the time. Mongol Yuan Dynasty During the Yuan Dynasty (1271–1368), contacts with the West also brought the introduction to China of a major food crop, sorghum, along with other foreign food products and methods of preparation. Hu Sihui, a Mongol doctor of Chinese medicine, compiled the Yinshan Zhengyao, a guide to cooking and health which incorporated Chinese and Mongol food practices. The recipes for the medicines are listed in a fashionable way which allow the readers to avoid lingering over the descriptions of the cooking methods. For instance, the description included the step by step instructions for every ingredients and follow by the cooking methods for these ingredients. Yunnan cuisine is unique in China for its cheeses like Rubing and Rushan cheese made by the Bai people, and its yogurt, the yogurt may have been due to a combination of Mongolian influence during the Yuan dynasty, the Central Asian settlement in Yunnan, and the proximity and influence of India and Tibet on Yunnan. Ming dynasty China during the Ming Dynasty (1368–1644) became involved in a new global trade of goods, plants, animals, and food crops known as the Columbian Exchange. Although the bulk of imports to China were silver, the Chinese also purchased New World crops from the Spanish Empire. This included sweet potatoes, maize, and peanuts, foods that could be cultivated in lands where traditional Chinese staple crops—wheat, millet, and rice—couldn't grow, hence facilitating a rise in the population of China. In the Song Dynasty (960–1279), rice had become the major staple crop of the poor; after sweet potatoes were introduced to China around 1560, it gradually became the traditional food of the lower classes. Because of the need for more food, prices went up and more of the lower class citizens died. Qing dynasty Jonathan Spence writes appreciatively that by the Qing Dynasty the "culinary arts were treated as a part of the life of the mind: There was a Tao of food, just as there was Tao of conduct and one of literary creation." The opulence of the scholar-official Li Liweng was balanced by the gastronome Yuan Mei. To make the best rice, Li would send his maid to gather the dew from the flowers of the wild rose, cassia, or citron to add at the last minute; Li insisted that water from garden roses was too strong. Yuan Mei