The aroma of wine consists of 600 to 800 aroma compounds from which especially those, typical for the variety, are already present in the grapes. There are significant varietal differences between the aromagrams ('fingerprint patterns'). Thus the amount of some flavour compounds ('key substances') shows typical dependence on the variety. Especially monoterpene compounds play an important role in the differentiation of wine varieties. The German white wines can be differentiated into three groups only by quantitative determination of 12 monoterpenes ('terpene profile'). These groups are: 'Riesling type', 'Muscat type' and 'Silvaner-Weissburgunder type'. Such 'terpene profiles' are also useful for the separation of real Riesling wines from others called Riesling (e.g. Welschriesling, Kap Riesling, Emerald Riesling) but not produced from grapes of the variety Riesling. Including further components and by means of statistical methods (discriminant analysis) even the different varieties within the mentioned groups for instance the 'Riesling'-group (e.g. Riesling, Kerner, Ehrenfelser, Bacchus, Müller-Thurgau) can be separated from each other. An analytical characterization of the neutral ('Silvaner-type') grape varieties Silvaner, Ruländer (Pinot gris), Weissburgunder (Pinot blanc) is also possible with about 20 compounds (e.g. monoterpenes, alcohols). Computing at the same time free and glycosidically bound aroma components (monoterpenes, alcohols, norisoprenes) in discriminant analysis the characterization of the neutral grape varieties can be considerably improved. To identify compounds causing 'off-flavours' sniffing technique is the method of choice. The off-flavour is pinpointed during gas chromatographic separation of the complex aroma mixture by effluent sniffing. Once allocated, the chemical nature of the off-flavours is elucidated by spectroscopic methods. Substances contributing to the green pepper taint, the strawberry note, moussiness, corkiness, etc. in wine could be found in this way.