What do we know about the kerosene/petrol aroma in riesling wines?
AIM: 1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) is a controversial aroma component found in Riesling wines. It belongs to the family of C13-norisoprenoids and is mainly associated with kerosene/petrol notes. TDN can add complexity to the wine aroma at medium – low concentrations and deteriorate the wine bouquet when its content is high. No TDN aromas are usually perceived in young Riesling wines, but they can appear after several years of aging due to the gradual formation of TDN. Management of TDN in Riesling wines is an actual task, since global warming can promote formation of this compound and compromise the aromatic composition of wine. Therefore, the aim of the current work was, firstly, to study the sensory particularities of TDN in Riesling wine at various concentrations. Secondly, to investigate the ability of bottle closures to absorb (scalp) TDN from Riesling wine under various storage conditions. These studies also include the comparative assessment of our findings with previously published data.
METHODS: sensory analysis, GC-MS (SBSE), HPLC,1H-NMR and other methods related to the synthesis and determination of TDN.
RESULTS: First of all, the method of the synthesis of highly purified TDN (95% and 99.5%) was optimized . The obtained TDN was used for the calibrations in GC-MS analysis and for the sensory and TDN scalping studies. As a result, three sensory thresholds for TDN in Riesling wine were determined: detection threshold (about 4 μg/L), recognition threshold (about 10-12 μg/L) and rejection threshold (about 71-82 μg/L) . It was also demonstrated, that the TDN aroma recognition was easier in the cooled wine. The defined thresholds were discussed in relation to the previously reported sensory thresholds determined by other panels and in other wine matrices. In the experiment of TDN scalping, five bottle closures were studied under storage conditions which varied by ambient temperature (14 °C vs 27 °C) and bottle position (horizontal vs vertical) . A large difference in TDN scalping rate was observed for synthetic and glass stoppers depending on the storage conditions. For example, the TDN absorbance from the wine was more than three times faster by synthetic stoppers at the lower storage temperature compared to the higher one (vertical bottle position). Cork stoppers demonstrated a fast scalping process in all storage scenarios, absorbing up to 40% TDN. In the wine bottled with BVS screw caps, only a minor decrease of TDN was found in all storage variants.
TDN is an aroma compound that requires effective control tools in Riesling wines. The described results of the sensory analysis can be used as a reference for the desired content of TDN in finished Riesling wines. At the same time, the outcomes of the TDN scalping study provide a deeper understanding of the impact of bottle closures and storage conditions on the TDN content in wine.
Issue: Macrowine 2021
(1) Hochschule Geisenheim University (Germany) (2) Faculty of Chemistry, Taras Shevchenko National University of Kyiv (Ukraine)
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1,1,6-trimethyl-1,2-dihydronaphthalene (tdn); sensory threshold; scalping; bottle closure; wine