A bronze yan from Zhongshancheng tomb from the Warring States Period. [File photo/IC]

4. Bronze Yan: ancient steamer

Although the "Wen Ding" was effective at keeping food warm, the ancient Chinese people later found that its burning process produced pollution. As a result, the bronze yan was made with a two-tier structure and used to steam rice and other grains. After the Eastern Han Dynasty (AD25 - AD220), further improvements to the bronze yan that led to the modern-day steamer.