Riesling acetal is a precursor to 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) in wine

Background and Aims: Knowledge of the formation and fate of aroma compounds is important to an understanding of the processes that affect wine composition and flavour. This study aimed to investigate the competitive formation and degradation of 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) and 2,2,6,8-tetramethyl-7,11-dioxatricyclo[6.2.1.01,6]undec-4-ene (Riesling acetal) under wine storage conditions. Methods and Results: 1,1,5-trimethyl-3,6-dihydroxy-9,9-ethylenedioxymegastigm-4-ene was synthesised in the laboratory by using standard organic chemistry transformation methodology and was subsequently used to prepare both Riesling acetal and TDN. At 45°C in model wine, approximately 40% of Riesling acetal was converted to TDN after 60 days at pH 3.2, whereas 80% was converted after 60 days at pH 3.0, as established by GC/MS analysis. Under more vigorous conditions, this conversion was complete and the TDN thus formed was completely stable. Conclusion: Riesling acetal is a precursor to TDN at wine pH, rather than a competing end-product formed by the acid-catalysed hydrolysis of precursors common to both compounds. TDN is chemically stable to wine acid. Significance of the Study: The findings provide a clearer understanding of the factors affecting the concentration of TDN (kerosene, bottle-age aroma) in older wines and thereby have the potential to indicate strategies for modulating the formation of TDN.Merran A. Daniel, Dimitra L. Capone, Mark A. Sefton and Gordon M. Else