Riesling grapes, which originate in Germany's Rhine region, have sweet fruity flavors and aromas of flowers and fruits. Other characteristics of wines made form Riesling grapes include high acidity and petrol notes if aged. The character of a Riesling wine depends heavily on where it is grown because Riesling grapes are very 'terroir expressive.' Rieslings cannot be oaked like Chardonnays and the oak flavor is part of what draws people to Chardonnay.
Rieslings & Terroir
Many people tend to associate Riesling wines with sweet dessert wines and it's true that many Rieslings can be quite sweet. Rieslings are, however, much more complex than that. Riesling grapes have the ability to absorb a great deal from their environment when they grow. Because Rieslings grow best in rocky ground, especially soil dominated by slate and flint, Rieslings are generally characterized by minerally aromas and flavors. In fact, you can often tell you're drinking a Riesling as opposed to some other wine because of the mineral characteristics.
It is common to drink white wines while they are young and only age red wines; this is because red wines posses chemicals which preserve the wines over the course of decades while white wines tend to spoil. One exception to this trend is the Riesling wine because its high acidity protects it in a manner similar to how red wines are protected.
Most Rieslings are not aged but are instead drunk young, when they are sweet, fruity, and aromatic. If a Riesling is good enough, though, it can be aged for decades or even centuries in the proper conditions. Although most aged Riesling are one or two decades old, it's possible to find Rieslings dating back to the 17th century. When aged, Rieslings become golden or amber in color and much more complex in their flavors. One aspect of this complexity which some object to are hints or notes of petroleum, like kerosene.