New Delhi, Feb. 7 -- I think I've unconsciously built a mental map of tea over the years, setting my preferences to Indian/south Asian black teas, Chinese whites, Taiwanese oolongs, and Japanese greens - maybe even a Kenyan purple. It's of course, shaped by habit and familiarity. Every now and then, though, a tea comes along that nudges those borders a little as it happened this week.

Some time ago, Taiwanese producer and exporter Sean Hsu Hao Sheng, of Trilliant Tea, sent me a few oolong samples. I had reciprocated with some Indian blacks, and keeping the tea-off going, he replied with Taiwanese black teas.

More famous for its oolongs, these black teas were like being let into a secret world. Of the teas I received, the Ruby black tea,...