It is coffee without sugar. Café forte = strong coffee, café preto = black coffee (without milk)
So, that's why "sour" would be incorrect as well, yes? Besides that it makes little sense in English, I mean.
In Portugal, "um café" will get you a standard black espresso with sugar on the side (just do not use it).
There are a lot of way to dress up the basic espresso, but few places serve the standard American drip coffee (or even French Pressed).
Unlike in the UK, milk is not automatically added to coffee in Portugal, though sugar is ever present (but it is left to you to put in to your taste).
I've never known anyone who likes bitter coffee. Bitter coffee is coffee that was left on the heat too long. "Café amargo" is coffee without sugar. We use the same phrase in Spanish.
Vietnamese men really like bitter coffee. It has a very typical smell that can makes you wasted
I wrote: The commander likes a bitter coffee. Why is the "a" cant be a good answer?
I didn't try this, but The commander likes unsweetened coffee is probably the most apt translation for this.
Could it be translated as strong coffee - I put bitter and got it right but thought it might mean strong coffee