Jiangmen — the prefecture in the western Pearl River delta that brands itself 中国侨都 (Zhōngguó Qiáodū, China's "overseas-Chinese capital") — did not grow a single coffee bean when its coffee industry began. What it had instead was a diaspora. For more than a century the people of the five Wuyi counties — Taishan, Kaiping, Xinhui,…