By Elyssa Goodman Inside the large, silver industrial coffee roasters at Shared Roastery in Brooklyn, Nguyen Coffee Supply’s robusta beans are heating up. After about 12 minutes and some 400 degrees, founder Sahra Nguyen offers me a sniff: the beans, imported directly from Vietnam, smell of warm, toasty and sweet caramel. Robusta beans are hearty, able to endure all manner of climate changes, and produce a coffee that is itself lower in fat and sugar and higher in caffeine. They have thrived in Vietnam since the early 20th century, the bean behind a slow coffee culture that prizes relaxation a…