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"My coffee has become tepid." To a coffee drinker, is there any realization more sigh-inducing?

It is strange, when you think about it, that a piping hot cup o' joe can be so delicious, and that iced coffee can be very nice, too, but that between those temperature extremes there lies an unpleasant no-man's-land of bitterness. Room-temperature coffee is regularly tolerated by us all — ok, us "addicts" — because we can't function without the caffeine. But why does it taste so bad?