In coffee, "acidity" means brightness and liveliness — think the sparkling quality of a green apple or citrus — not sourness, and not something that necessarily upsets your stomach.
The Simple Guide
High-altitude coffees, especially washed-process coffees from East Africa and parts of Central America, tend to have brighter, more pronounced acidity. Lower-altitude coffees and darker roasts tend to taste flatter and less acidic.
Why It Matters
Good acidity tastes "juicy" and lively, not sour. If a coffee actually tastes sour or vinegary, that's usually a brewing problem (under-extraction), not a trait of the coffee itself.
What To Do
Like brightness? Look for washed-process, high-altitude, light-roast coffees from Ethiopia, Kenya or Colombia. Prefer a rounder, softer cup? Choose lower-altitude origins or a darker roast.
If your coffee tastes sharp or sour in a way you don't enjoy, before writing off the coffee itself, check your brew — it's very often under-extraction, not the bean.