Vietnamese coffee from concentrate? I was in a banh mi shop today and ordered a hot Vietnamese coffee. The shopkeeper put some refrigerated concentrate and condensed milk in the cup, and then added hot water. Is this a standard method for selling large volumes of Vietnamese coffee? And if so, how is the concentrate made? Is it a cold brew method like this, or do they do it some other way?

NB: I'm in the US, if it matters.
Apparently they used some sort of a pour over method, I'm not very sure about it though because they wouldn't expose their trade secrets to me ;). 

What I am sure is it is common practice for the Vietnamese to sell from concentrate, because they brew a batch in one go then refrigerate it until it is used, not unlike cold brews. If you're a fan of espresso, you can drink the concentrate straight up.

Source: A Vietnamese coffee seller during a trip