Acidity vs sourness

The same chemistry described two ways. Acidity is bright and integrated; sourness is sharp and separate — and usually acetic.

Why these get confused

Tasting notes praise acidity and condemn sourness, which reads as inconsistent. The difference is which acids and how well integrated they are.

	Acidity	Sourness	Why it matters
Which acids	Predominantly citric, malic and lactic — the fruit acids, formed during fermentation.	Predominantly acetic acid, which is vinegar.	This is the substantive difference. Acetic acid should have driven off during drying and conching; where it has not, the chocolate reads sour.
How it presents	Lifts the fruit notes and makes the bar feel bright.	Sits on top as a sharp separate note, sometimes distinctly vinegary.
What it indicates	Good fermentation and a light enough roast to preserve it.	Under-drying, or a short dry-conch that never drove off the residual acetic acid.	A sour bar is usually a processing shortfall rather than a stylistic choice, though very light roasting can produce it too.
Pairing consequence	Pairs well with cream and fat, which round it.	Pairs badly with almost everything acidic; the sharpness compounds.

Describe a bar as acidic when the brightness is integrated and lifts fruit character — Madagascar is the reference case.

Describe it as sour when the sharpness sits apart from the chocolate, particularly with a vinegary edge.

ChocolateHQ editorial synthesis — ChocolateHQ(citation identity confirmed; passage not re-read)
Chocolate Science and Technology — Wiley-Blackwell(citation identity confirmed; passage not re-read)
The Science of Chocolate — Royal Society of Chemistry(citation identity confirmed; passage not re-read)