star (2013-09-26)
O aromatach nafcianych Rieslinga mowa na (pralinka) Wine-Pages.com.

In addition to the intensifying and complexing of terpenoid aromas, bottle-ageing induces Riesling's famous petrol (kerosene, gasoline or paraffin) aroma. Anyone who has ever siphoned-off petrol will know that its head-splitting vapour has nothing in common with the classic petrolly aroma of a mature Riesling. It does not literally smell or taste of petrol. Yet for those who know and enjoy the zesty-honeyed richness of a great Riesling, petrolly is one of the most precisely defined, exquisitely evocative words in the wine tasting vocabulary. Some critics might come up with a veritable fruit-salad of descriptors, only some of which may be recognised by equally experienced tasters, but there is not one iota of doubt in the mind of anyone who has ever experienced the classic petrolly aroma of a mature Riesling that it is an instantly recognisable term, and one that is used without pretension. But what causes it, and is it possible to have too much of this good thing?
Riesling's so-called petrol aroma has been identified as trimethyldihydronaphthalene or, to be precise, 1,1,6-trimethyl-1,2-dihydronaphthalene (Simpson, 1978). TDN is a C13 norisoprenoid, which some class as a terpene, but others do not. It is a moot point; a semantic argument upon which chemists continue to differ. TDN is rarely found in grapes or, indeed, young wine, although its precursors are, and they are primarily carotenoids (may chemists state definitely beta-carotene, others probably alpha-carotene, while some think quite possibly both). Beta and alpha carotenes (and lutein a by-product of alpha carotene metabolism) are all antioxidants. These precursors exist in all grape varieties, thus TDN can be found in almost every wine, although the ratio of lutein to carotene is usually low, thus the TDN potential for most wines will be well under the perception threshold level of 20ppb. However, the ratio of beta carotene to lutein is higher in Riesling than for any other grape variety. If ,as most scientists believe, beta carotene is the primary precursor for TDN, this may explain why, after lengthy bottle-maturation, the wines from this variety can accumulate as much as 200ppb TDN, ten-times the perception level. This is why mature Riesling is famed for its so-called petrolly aroma.
TDN can also be produced by the hydrolysis of two megastigma-3,6,9-triols linked to a sugar molecule (Strauss et al, 1986) and it has been theorised that the hydrolysis of a sugar molecule called 2,6,10,10-tetramethyl-1-oxaspiro[4,5]dec-6-ene-2,8-diol can create TDN (Winterhalter, 1991; Silva Ferreira & Guedes de Pinho, 2004)
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