Light vs dark roasting

Light roasting preserves origin character and exposes defects. Dark roasting builds cocoa depth and covers them.

Side by side

	Light roast	Dark roast	Why it matters
What survives	Fruit, floral and acid notes from fermentation.	Maillard-derived cocoa, coffee and toast notes; origin character largely gone.	This is the whole decision. Light roast is a bet that the beans are worth hearing; dark roast is a decision to make the chocolate rather than the bean.
Tolerance of poor beans	Very low. Under-fermentation, mould and smoke taint all come through.	High. Roast character masks a great deal.	Dark roasting is the correct choice for variable commodity beans, which is why industrial chocolate uses it.
Acidity	Retained, sometimes to the point of sourness.	Reduced, as volatile acids drive off.	A bar that tastes aggressively sour has usually been roasted too lightly for its beans, not fermented badly.
Risk of a green note	Real. Too light and the fermentation precursors never convert.	Nil, but burnt notes take its place at the far end.

For fine-flavour beans where the fermentation was well managed and the origin has something to say.

For bulk beans, for classic deep cocoa character, and where consistency across variable lots is required.

Light roastingSet against Dark roast, with the practical consequence of each difference.
Dark roastingSet against Light roast, with the practical consequence of each difference.

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