1,1,6-Trimethyl-1,2-dihydronaphthalene Content of Riesling Wines in Hungary.

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) is known to give a petrol note when smelling and tasting wine, which is most pronounced in Riesling varieties. Its increasing concentration has been linked to climate change. In the present work, a gas chromatographic method was used to quantify free TDN in "Italian Riesling", "Rhine Riesling", and "Kéknyelu" wines from Hungary. From the vintages 2010 to 2020, 39 bottles of wine from different wine regions were evaluated by instrumental analysis and sensory evaluation. Our aim is to determine the extent to which the Riesling wines in Hungary show a petrol character. The other objective was a comparison of sorts to see if there is a difference in TDN production potential between Italian Riesling and Rhine Riesling. We also aimed to clarify the question whether the Hungarian variety Kéknyelu is also capable of developing a petrol character. The wines we tested were corked and screw-locked. This allowed us to compare the difference in TDN concentration variation over time between the two closure methods.

Anaerobic organic acid metabolism of Candida zemplinina in comparison with Saccharomyces wine yeasts.

Organic acid production under oxygen-limited conditions has been thoroughly studied in the Saccharomyces species, but practically never investigated in Candida zemplinina, which seems to be an acidogenic species under oxidative laboratory conditions. In this study, several strains of C. zemplinina were tested for organic acid metabolism, in comparison with Saccharomyces cerevisiae, Saccharomyces uvarum and Candida stellata, under fermentative conditions. Only C. stellata produced significantly higher acidity in simple minimal media (SM) with low sugar content and two different nitrogen sources (ammonia or glutamic acid) at low level. However, the acid profile differed largely between the Saccharomyces and Candida species and showed inverse types of N-dependence in some cases. Succinic acid production was strongly enhanced on glutamic acid in Saccharomyces species, but not in Candida species. 2-oxoglutarate production was strongly supported on ammonium nitrogen in Candida species, but remained low in Saccharomyces. Candida species, C. stellata in particular, produced more pyruvic acid regardless of N-sources. From the results, we concluded that the anaerobic organic acid metabolisms of C. zemplinina and C. stellata are different from each other and also from that of the Saccharomyces species. In the formation of succinic acid, the oxidative pathway from glutamic acid seems to play little or no role in C. zemplinina. The reductive branch of the TCA cycle, however, produces acidic intermediates (malic, fumaric, and succinic acid) in a level comparable with the production of the Saccharomyces species. An unidentified organic acid, which was produced on glutamic acid only by the Candida species, needs further investigation.