@phdthesis{Grebneva2022, author = {Grebneva, Yevgeniya}, title = {The formation, sensory contribution and management of 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) in grapes and wines of Vitis vinifera L.cv. Riesling}, volume = {2022}, edition = {1. Auflage}, publisher = {Gesellschaft zur F{\"o}rderung der Hochschule Geisenheim}, address = {Geisenheim}, url = {http://nbn-resolving.de/urn:nbn:de:hebis:2083-387}, school = {Hochschule Geisenheim University}, pages = {220}, year = {2022}, abstract = {Wine from Vitis vinifera cv. Riesling grapes is one of the most internationally renowned white wine styles worldwide. There are several aroma compounds that are fundamental to the sensory properties of Riesling wines. Two such classes of compounds are monoterpenes and C13-norisoprenoids, both of which can be influenced in the vineyard, the winery and in the bottle. The overall objective of this study was to investigate the role of certain vineyard and winemaking practices on the development of sensorial important flavour compounds in Riesling, with particular emphasis on 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN). Chapter 2 investigates the effect of a manipulated light environment during grape ripening on Australian Riesling over two consecutive vintages. The application of coloured shade cloth was used to alter not only the quantity of light but also the quality of light reaching grape leaves and berries. Changes in both grape and wine composition were observed. A reduction solely in the quantity of light resulted in a significant reduction in free and total TDN concentrations. However, sensory descriptive analysis of finalised wines demonstrated a conflicting result, as increased 'kerosene-like' aroma (a common descriptor for TDN) was not always linked to higher TDN concentrations. The starting point of TDN formation is the availability of its precursors; carotenoids and their subsequent glycosylated breakdown products. Chapter 3 comprises the analysis of major grape carotenoids present in grapes under various light conditions. While several complex mechanisms involved in photosynthesis and notably the photoprotection triggered by different light qualities during the ripening period were observed, the reduction in concentration of carotenoids was significantly higher in sun-exposed samples compared to other treatments during grape ripening. The degree of carotenoid degradation could be a useful marker for the decision regarding TDN management in wine during winemaking or storage. Furthermore, Chapter 3 provides results from the analysis of C13-norisoprenoid glycosides in wines made from grapes grown under different shade cloth in correlation to their corresponding TDN concentrations. For this experiment two approaches were considered, firstly the untargeted profiling and then targeted analysis of the glycosides in wine. Glycosides related to TDN evolution in wine were tentatively identified. While trials conducted in Australia evaluated the effect of shading on the evolution of important grape and wine components in Riesling, Chapter 4 describes the significance of increased solar exposure (leaf removal) on Riesling grape and wine compositional behaviour in combination with different row orientations (East-West, Northeast-Southwest, North-South) under German field conditions. Microclimatically, East-West orientated rows maintained the lowest interior canopy light interception, Northeast-Southwest and North-South orientations lead to the highest light exposure values, peaking in the morning and afternoon, respectively. Pronounced differences in secondary metabolites were found between the different exposure levels introduced by leaf removal. Highly exposed grapes showed significantly higher bound and free TDN concentrations, however, no direct correlation was observed between elevated free TDN levels and the perception of 'kerosene-like' aroma in the wines. Finally, Chapter 5 comprises a comparative analysis of oenological practices of grape pressing and yeast selection including enzyme (β-glycosidase) addition on the extraction of TDN and related C13-norisoprenoids in finished wines. Insignificant differences were observed between the effect of whole-bunch and crushed/destemmed fruit pressings. While the choice of yeast during alcoholic fermentation did not affect TDN formation, the addition of glycosidases to musts resulted in an approximately 15\% to 25\% increases in free TDN concentrations after the wines were submitted to accelerated ageing. However, these changes were negligible when compared to the consequence of viticultural management practices. This thesis represents a valuable contribution to the understanding of the formation, management and sensory contribution of TDN in Riesling. Furthermore, this study investigated for the first time the effect of different light regimes (shade cloth) on TDN evolution which can be used to advance the management of Riesling grape production, especially during hotter summers.}, language = {en} }