The aeration and moderate heat causes as much as 80% of the
volatile aromatic compounds (and excess
moisture) to evaporate out of the chocolate
liquor. Fortunately, many of these are undesirable volatiles, including various acids
and aldehydes; acidity steadily declines during conching. At the same time, a number
of desirable volatiles are augmented by the
heat and mixing, notably those with
roasted, caramel, and malty aromas
(pyrazines, furaneol, maltol).