A wider glass gives the wine more room to breathe, while a narrower rim helps direct the aromas. The shape of the glass also directs the wine toward a specific part of the tongue. We perceive saltiness on the left and right sides, and sweetness at the tip
Acidity is perceived on the left and right sides of the tongue, but in the middle part of it, while bitterness is detected at the back, towards the root. The glass is shaped to direct the wine to the area where the most important flavor is best perceived.
Larger glasses helps wine aeration, softening the tannins and opening up the flavor. That is why they are used for red wines, as well as for amber wines, which are made from white grapes but vinified using the method for reds.
Pinot Noir, for example, is a lighter red wine that shines in a large, tulip-shaped glass, which helps highlight the variety's subtle, floral aromas. The glass for a mature Cabernet Sauvignon is said to be diamond-shaped, very large diamond. The size of the glass is important for allowing the varietal aromas to open up.