Why is white wine served chilled and red wine at room temperature?

Chilling a wine brings out its acidity. White wines tend to have pronounced acidic flavors- think of the grapefruit aromas in a Marlborough Sauvignon Blanc or lemony flavors in an Italian Pinot Grigio. If a wine is served too cold, you may miss out on other flavors, and your wine could taste tart or even metallic. Conversely, a warm white wine will usually be flat and unrefreshing.

Red wines are generally better served at cellar temperature- somewhere around 55 or 60 degrees F. My personal experience is that cold red wine does have interesting flavors, but is also bitter and too tannic.

A good way to find your personal preferences is to put a heavy chill on your whites, then let the bottle come to room temperature as you drink it. You will see a wide array of flavors, and even find whites that improve as they warm. I've also found that it is nice to put a light chill on reds and drink them the same way- you will notice new aromas as the wine changes temperatures.