Tea, and the long habit of paying attention.

Lu Yu 陸羽 (c. 733–804) was raised in a Buddhist monastery and spent his life on a single subject. Some time around 760–780 he finished 《茶經》, the Classic of Tea: three scrolls, ten chapters, covering the plant's origins, the tools for making it, the manufacture, the vessels, the boiling, the drinking, the historical record, the growing regions, what may be left out when travelling, and how to copy the whole thing onto a scroll and hang it on the wall.

Before him, tea in China was a regional drink boiled up with salt, ginger, orange peel and whatever else was to hand. Lu Yu thought this was barbarism and said so. He ranked waters by their source. He described the three stages of the boil by the look of the bubbles — fish eyes, then a string of pearls at the edge, then turbulent waves — and insisted the tea went in at the second.

The lasting achievement is not the recipe, which nobody now follows. It is that tea acquired a vocabulary, and therefore an argument. From the Tang onward it was possible to be wrong about tea, which is the precondition for taking anything seriously.

Song drinkers did not steep. They ground steamed and pressed tea to a flour-fine powder, warmed a bowl, made a paste with a little hot water, and then whisked with a split-bamboo 茶筅 while adding more water in stages, raising a dense white froth. This is 點茶, diancha.

It became competitive. In 鬥茶 contests, players were judged on the whiteness of the froth and on how long it clung to the wall of the bowl before a watermark appeared at the rim — last mark wins. Because the prize was whiteness, the bowls were black: 建盞 Jian ware from Fujian, glazed in dark iron with streaks the potters called 兔毫, hare's fur. Emperor Huizong 宋徽宗 — an indifferent ruler and a serious aesthete — wrote a treatise on the method, 《大觀茶論》, in 1107.

Whisked tea did not survive the next dynasty in China. It did survive in Japan, where it had been carried by monks and became matcha. When people say the Japanese tea ceremony preserves something China lost, this is the specific thing they mean.

In 1391 the founding Ming emperor, Zhu Yuanzhang 朱元璋, abolished the compressed cake tea that provinces had been sending to the court as tribute and ordered loose leaf sent instead. He had come up from poverty and regarded the pressed cakes — laborious, ornamental, extracted from farmers — as waste.

The effect on how China drank was total. Powder and whisk became pointless overnight. Whole leaves needed to be steeped in a vessel and poured off, which is 散茶, loose tea, and which is still, six centuries later, what almost everyone does.

It also created a demand for a small pot that held heat and did not fight the tea. The answer came from Yixing 宜興 in Jiangsu: unglazed 紫砂 zisha stoneware, slightly porous, taking on the character of whatever is brewed in it. The Ming turn to loose leaf is why a yixing pot exists at all, and why a serious owner keeps one pot to one kind of tea.