Petrol and riesling
After my recent tasting of a Michel Chapoutier Alsace 2012 riesling and referring to his earlier suggestion, reported in 2011, that petrol is a fixable fault, I felt it was time to revisit this evocative area, to see how his wines perform, and what the thinking might be now …
Firstly, as the major producer, what do the Germans think? The German Wine Institute (3) has marketed an aroma wheel since before 2005, and this makes no reference to hydrocarbon-based notes eg petrol, diesel, oil, kerosene (heating oil), slightly odd, as those aromas are an expected feature of high quality aged riesling.
Does the Institute consider a petrol note a fault? It appears so, and more than one producer concurs (11). It may be that petrol in wine is not considered good marketing – but it is part and parcel of aged riesling, at least for the cognoscenti. This omission adds to the lack of clarity already presented by the German wine industry to the potential consumer, through for example its proliferation of classification systems (some better than others), uncertainty over residual sugar level, complex multiple labelling systems, introduction of even more labelling terms – classic and selection, never mind the re-entry of Blue Nun and Black Tower to the supermarket shelves, clouding ideas of quality … At the other end of the ageing spectrum, a petrolly note in a young riesling, where fresh fruit flavours of apple, grapefruit and lime are anticipated, is unwelcome in my view.
Michel Chapoutier (2) suggested petrol was a fault induced by over-pressing. His Alsace wines, with a first vintage in 2009, use very gentle pressing, but the example tasted, above, with barely 3 years of age under its belt in 2016, means the jury is still out. I am trying to locate and assess the 2009.
My pet theory is that petrol evolves out of lime, which can be found regularly in young(ish) riesling, as well as aged examples. Checking through my 24 riesling tasting notes to date, covering a range of origin, age and style, lime appeared 16 times on the nose and 19 on the palate. A petrol note can add another dimension to the complexity of an aged honeyed riesling – but if it is overwhelming, even after decanting and giving time, then it could be described as a fault. When I am tasting a riesling with a group, not everyone appreciates petrol nuances, my suggestion is to lie back and think of lime, which is not a million miles away from petrol.
The source of the petrol note is the chemical compound TDN or trimethyl-dihydronaphthalene (11). TDN is created during ageing, by acid hydrolysis of terpenes, specifically of carotenoid precursors. TDN levels are directly affected by elevated levels of these precursors, which are found in …
- riper grapes (so relatively lower acidity – but remembering riesling has naturally high acidity) from …
▪ a long hang time
▪ sites with a high level of insolation and heat absorption
- grapes with higher acidity
… both points are highly relevant to the production of low yield, high quality riesling, with a long ageing potential, from sites with optimal exposure.
TDN levels are highest in riesling, and given time in cellar, no matter their origin or vinification processes, most riesling will develop a petrol note. The realisation of TDN as a petrol character in riesling is thought to be accentuated by:
- water stress eg Alsace, Rheingau and Clare Valley – but outside the EU one may mitigate this with irrigation
- slow oxidative bottle ageing and/or oxidative handling in the winery
… again, both are relevant to high quality ageworthy and ageing riesling.
Drawing up some rules for TDN level and potential for a petrol note …
- high levels of sun exposure and ripeness = high levels of TDN and petrol potential, and conversely …
- low levels of sun exposure and ripeness = low levels of TDN and petrol potential
In case (1), the most relevant to quality riesling, the potential for a petrol note to be realised in a wine, then depends on water stress and oxidation. There seems less certainty concerning the latter, and by extension its opposite, reduction, hence the question marks below …
- high level of petrol potential + water stress + oxidation? = more petrol character (eg Alsace and Germany)
- high level of petrol potential + irrigation + reduction? = less petrol character (eg Clare Valley)
There are intermediate cases where for example, the petrol character may be reduced through relief of water stress by managed irrigation, but then possibly increased again by oxidative practices in the winery. So the relationship is not straightforward.
It seemed of interest to consider the time-lapse from vintage to a petrol/kerosene/rubber note emerging. I reviewed many community tastings of the same wine over time, using Cellar tracker (12). Results suggest, across a wide range of terroirs eg Alsace, Rheingau, Finger Lakes, Oregon, Clare Valley and Washington, that petrol notes, at a discernible level, may arise as soon as 1-2 years post vintage. There are exceptions, eg Howard Park in the Great Southern (9), but that will always be the case.
- Are Petrol Notes In Aged Riesling A Fault? (Thoughts On A Clare Valley Master-class). [online]. Accessed 20/03/16.
- Petrol smell in riesling a mistake: Chapoutier. (2011). Lechmere, A. Decanter Magazine. [online]. Accessed 20/03/16.
- Riesling – petrol or a fault. My post. (2012).
- Chapoutier Schieferkopf Buehl 2012. My tasting note (2016).
- M.Chapoutier Riesling Schieferkopf. [online]. Accessed 20/03/16.
- The German Wine Institute, operated under Wines of Germany. [online]. Accessed 20/03/16.
- Mitchell Watervale Riesling Vertical 2000 – 2006. undated. Marsh, C. [online]. Accessed 20/03/16.
- The contours of riesling – a vertical tasting. 2010. Jorgensen, N. [online]. Accessed 20/03/16.
- Howard Park riesling vertical 1986-2014, Great Southern, Western Australia. 2014. [online]. Accessed 20/03/16.
- Foreign Affair Winery, Niagara, Canada, Riesling vertical collection 2011-2013. (2014?)
- Rheingold, the German Wine Renaissance; pp.95-96. (2005). Bird, O. Arima Publishing.
- Cellar tracker. [online]. Accessed 22/03/16.