There's no doubt that food tastes different when it's hot. Part of the reason is that heat brings out more of the aroma, and our sense of taste relies a lot on how things smell.
But there's more to it, according to the February 2000 issue of the journal Nature. Heat can stimulate taste buds, so that they send a signal back to the brain. For example, if you put something warm on the front edge of your tongue, you'll get a sensation of sweetness. That's because the nerves that are being stimulated only know how to send one message to the brain: the sensation of sweetness.
The brain can't tell if the nerves were stimulated by a chemical, such as sugar, or something else, such as heat. Cold temperatures usually cause a sour or salty taste.
Maybe that's why a warm soda tastes too sweet, and a cold soda tastes just right.
