The taste buds that register bitterness are concentrated at the back of the tongue. Tannin in a wine translates into bitterness and astringency. Wines in which the tannin overshadows the fruit can be brought into balance by a shape that allows the wine to flow onto the front and away from the back of the tongue where it's already highly tannic qualities would be magnified. A wine that is naturally low in acidity, like a Chardonnay , is best served by a glass that directs the flow of wine to the center of the tongue where the right balance of fruit and acidity will be experienced. Larger glasses are better for younger red wines, like a Bordeaux or Beaujolias .
More surface area is exposed to the air which releases more intense aromas, especially when swirled.
A small glass tends to inhibit the exposure to oxygen and that will enhance the bouquet of mature reds. If the cupboard holds any of those wide saucer-shaped champagne glasses like those seen in old movies, use them for desserts. The bubbles dissipate too fast and spills happen too easily. Try a tall tulip-shape flute that will direct the Champagne to the back of the tongue. The rim acts like a dam.