Just as chocolate and vanilla pair well, so do coffee and vanilla, hence the great popularity of vanilla-flavored coffees. Vanilla is also said to be the world’s favorite flavor overall. Back to vanilla and coffee, however, coffee purists tend to prefer adding vanilla as a flavoring after the coffee is brewed. Others are happy with the flavor roasted into the bean during processing. There are arguments both ways, of course.

Exactly how are coffees flavored, then, and when? The roasting comes first, that delicate mix of art and science that heats the green bean and turns it a rich aromatic …