Coffee alters the taste of foods eaten contemporaneously. Caffeine has nothing to do with it.
Sense of smell remains unaffected by coffee. But people “became more sensitive to sweetness, and less sensitive to bitterness,” reports flavor researcher Alexander Fjældstad. “It’s probably some of the bitter substances in the coffee that create this effect. This may explain that if you enjoy a piece of dark chocolate with your coffee, its taste is much milder, because the bitterness is downplayed and the sweetness is enhanced.”
Alexander W. Fjaeldstad & Henrique M. Fernandes, “Chemosensory sensitivity after coffee consumption is not static: short-term effects on gustatory and olfactory sensitivity,” Foods 9 (4): 493 (14 April 2020).
“Coffee alters perception of taste,” Sci News (21 April 2020).
Coffee image courtesy of Katie175