Large group of aromatic substances in wine, which are primarily perceived in terms of smell, but also in terms of taste and which have a significant influence on character and quality. These are mostly volatile compounds which are initially still odourlessly bound in the grapes as glycosides (sugar compounds). They are therefore called aroma precursors, from which the primary aromas develop during ripening. Soil type, temperature, exposure (sunlight) and water content in the soil have a great influence on the formation of aromas during the ripening period. The ideal condition is when the grapes are at their optimum physiological ripeness. By means of the measuring method glycosyl-glucose assay the aroma precursors in the grapes can be quantified and a quality prognosis can be made.