This one:
“Rafael Arroyo figured out how to make clean rum,” Wondrich said. “If you wanted rum to taste great before that, the standard way to do that would be to ship it to England where it would sit in the London docks in barrels, or to Bordeaux where it would sit in the docks in barrels, for years, and some of the sweatier components would come out.” The transport to Europe was part of the “recipe.” “But Arroyo said if you ferment it clean and distill it clean, you don’t have to go through all that.”
Lo and behold: shortly after I posted here, I saw Richard Seale had posted the link on Facebook overnight, with that exact quote.