Wines may be classified by their primary impression on the drinker's palate. They are made up of chemical compounds which are similar or identical to those in fruits, vegetables, and spices. The sweetness of wine is determined by the amount of residual sugar in the wine after fermentation, relative to the acidity present in the wine. Dry wine, for example, has only a small amount of residual sugar. However, a technically dry wine might taste sweet when it is not. For example, fennel might taste sweet, but does not contain much sugar.
Specific flavors may also be sensed, due to the highly complex mix of organic molecules such as esters and terpenes that grape juice and wine can contain. Tasters will also distinguish between flavors characteristic of a specific grape (e.g., Cabernet Sauvignon and blackcurrant) and flavors that are imparted by other factors in wine making, either intentional or not. The most typical intentional flavor elements in wine are those that are imparted by aging in oak casks, and virtually every element of chocolate, vanilla, or coffee are actually a factor of oak and not the native grape. Banana flavors (isoamyl acetate) are the product of yeast metabolism, as are spoilage aromas such as sweaty, barnyard, band-aid (4-ethylphenol and 4-ethylguaiacol), and rotten egg (hydrogen sulfide). Some varietals can also have mineral flavor, due to the fact that some salts are soluble in water (as limestone), and thus absorbed by the vine.
Wine aroma is the result of the interaction between components of the grapes and those produced during winemaking process, fermentation and aging. Being served at room temperature increases the vaporization of aroma compounds, making the wine more aromatic. For some red wines that are already highly aromatic, like Chinon and Beaujolais, the volatility of the wine makes it better served chilled.