A cup of traditional cà phê sữa đá is made with robusta beans, which have a sharper, bitter flavor than more mild arabica beans. The drink is available all over Vietnam, served at roadside cafes, restaurants and at home. But you won’t find the traditional style in a Starbucks. That’s because most international coffee chains only serve Arabica beans. It’s one reason global chains have struggled to grow in Vietnam’s more than $1 billion market for specialty coffee and tea shops.