Large group of aromatic substances in wine that are primarily perceived by smell but also by taste and have a significant influence on character and quality. Most of them are volatile compounds that are initially still odourless and bound as glycosides (sugar compounds) in the grapes. They are therefore called aroma precursors, from which the primary aromas develop during ripening. The type of soil, 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 given when the grapes are at optimal physiological ripeness. Using the glycosyl glucose assay measurement method, the aroma precursors in the grapes can be quantified and a quality prognosis can be made.