Ξ January 19th, 2009 | → 4 Comments | ∇ A Day at a Time, International Terroirs, Interviews, Technology, Wine History, Wine News, Wineries |
Who would have thought that a glass of wine could play a role in investigating fossil fuel emissions in the atmosphere? Well effectively that’s what scientists at the University of Groningen in the Netherlands have shown by analysing Carbon isotope levels in wine. Rather than dwelling on how wine leaves a Carbon footprint, these researchers have looked into how Carbon leaves a wine footprint!
I contacted the group to find out more about the work and to put some questions on what limitations were expected on using wine for this sort of research. Having received a copy of the paper I’ll try and summarise the key aspects first.
The burning of fossil fuels is currently the largest impactor on global atmospheric Carbon Dioxide (CO2) levels and in industrialised countries there is far more fossil fuel CO2 (CO2-ff) than from natural sources. Knowing the amount of CO2-ff is important in understanding CO2 exchange processes and also as a means of verifying emission reductions from agreements such as the Kyoto Protocol. Research scientist Sanne Palstra and her colleagues used some simple scientific facts to put together their research:
1) As grapes grow and develop they store sugars produced from vine photosynthesis – the daytime uptake of CO2 from the surrounding atmosphere. These sugars are fermented into alcohol to make wine.
2) Carbon Dioxide used for photosynthesis is predominantly from 2 sources – “natural” CO2 from the Biosphere (living world) and CO2 produced from the burning of fossil fuels (CO2-ff). These two types of CO2 differ only in one way, the amount of the Carbon isotope Carbon-14 (14C ), which is not present in fossil fuels.
3) The CO2-ff “contribution” in wine can be determined by analysing the 14C content of its alcohol and comparing it to expected levels of 14C from Biosphere sources only – any reduction in 14C should be due to excess CO2-ff in the atmosphere during grape development.
All living things contain Carbon, mostly in the stable Carbon-12 isotope, but a tiny proportion (approximately one part per trillion) of this Carbon is 14C. When any organism dies the amount of 14C in its remains slowly decreases over time due to radioactive decay, and as the hydrocarbons in fossil fuels are from organisms that died millions of years ago their 14C content is effectively zero. Carbon-14 may sound familiar to some of you, as it is the key player in the Carbon dating technique used in determining the age of archaeological finds from a few hundred to 50,000 years old.
In this new research the idea is not to date the sample using its 14C level, but to compare it to the expected amount for the year in question and use that information in trend analysis relating to fossil fuel use.
You may well ask why not just take these CO2 measurements directly from atmospheric testing, surely this is easier and more accurate that indirect measurement through a glass of wine? You’d be right of course, but, as the paper discusses, such measuring sites are labour intensive and expensive to maintain – there are only 11 such locations throughout Europe – and using wine analysis is a relatively easy and affordable way of supplementing such data.
Sanne explained more in a comment on the UK Science Museum site. Wine also has the added advantage of being able to provide data from the past, since vintage labels on the bottles confirm when the contents were grown.
In the research the group measured 14C levels from 165 different wines, covering 32 regions across 9 European countries. The wines used were predominantly from two time periods, 1990-1993 and 2000-2004. Tests were carried out only on the alcohol present in the wine, distilling a 100ml sample to gets pure ethanol only. Any remaining wine was enjoyed by family and friends of the group once their results had been analysed!
The first goal was to show that the results from the wine ethanol analysis agreed with air measurement results that were on record, and then to see if any regional trends could be determined. Industrial regions such as Northern Italy and Germany had clear indications of increased fossil fuel emissions and the paper also confirms that “we can distinguish wine areas in the vicinity of airports and cities (like Barcelona, Lecce and Bordeaux) from more remote regions”.
The lack of vineyard or winemaking details for most of the wines added an extra level of uncertainty to some of the results, since there was no way of confirming how specific an area the grapes had been sourced from or whether extra sugar had been added to the fermentation (as this sugar, and its ethanol, would not be representative of the local area or year). However one set of wines met more demanding analysis criteria – a flight of German wines between 1973 and 2004 from the same small town of Birkweiler in Rheinland-Pfalz where the researchers knew exactly the wine’s providence. Weingut Gies-Düppel provided wines from their Kastanienbusch and Mandelberg vineyards.
The winery is run by Volker Gies, son of the founders and a member of the Südpfalz ConneXion a small group of winemakers from the southern Pfalz area.
Having such a consistent set of wines for the 14C analysis allowed the study to look at trends in the Rheinland-Pfalz region as a whole and confirmed that an increase in fossil fuel consumption was likely over this 30 year time period.
I posed some questions to the group at the Centrum voor IsotopenOnderzoek (CIO) in Groningen. Unfortunately Sanne Palstra was off sick with ‘flu (I wish her a speedy recovery), but head of section Professor Harro Meijer kindly responded;
Could (chemical) treatments used in the vineyard affect the 14C levels?
Pr. Meijer: Not during growth. In the wine making (only) additions that become fermented to alcohol would influence the result, as then not all Carbon atoms in the wine alcohol are from the grape sugars.
Could differences in the winemaking process affect the analysis results?
Pr. Meijer: As long as the alcohol originates completely from the sugars in the wine grape we will get the same number, no matter what grape sort it has been, or how the exact fermentation conditions have been. Remember we distil the alcohol out of the wine, and do our analysis exclusively on that alcohol. Of course, if substances are added, like sugar addition and subsequent fermentation of that sugar to alcohol, we will notice deviations. Also, if wines from different harvest years are mixed, we will measure some average over those years. Oak barrels eventually pass some substances to the wine, but quantitatively this is very small, and it does not influence the alcohol.
If you tested a wine today, and then a bottle of the same wine 5 or 10 years from now, would there be any differences?
Pr. Meijer: It is the harvest time that counts, nothing else. The only thing that happens to the Carbon-14 of the alcohol is radioactive decay. Since we now exactly the rate of that process, we correct for decay. In the case of wine this correction is dependent on the time difference between the growth season of the wine grapes and the actual laboratory analysis time. In fact, using carbon-14 and knowing this decay rate, we can even measure the harvest year of a specific wine +/- 1 year or so.
Are you aware of any other wine related projects being undertaken?
Pr. Meijer: Not in this field, so far. Wine has been analysed for 14C before, but that was in the field of food authenticity and harvest year fraud. For this research, we could have taken any plant material, provided we know where and when it grew. In that respect wine is the only agricultural product which is stored in a site- and harvest-year specific way. And it is on sale everywhere!
With wine being one of the only agricultural products where a growing year is recorded it does offer some interesting potential for going back many years and looking at the 14C history.
Pr. Meijer: Actually, it would not make sense to use wine older than, say, 1975-1980 or so. This is caused by the nuclear bomb tests in the 1950’s and 1960’s. These produced a lot of artificial carbon-14, and it spread quite unevenly over the world. Before we can use carbon-14 in (atmospheric) CO2 again for detection of fossil fuel, the system had to “relax” for a decade or two. Only then, Carbon-14 was spread evenly enough over atmosphere and ocean water to become useful for fossil fuel detection again. So, no excuse for us to buy old wines on the research budget – alas!
Professor Meijer’s last comments quickly extinguished my thoughts on proposing a new project using old bottles of Tokaji or Bordeaux for further tests! Although not specifically discussed in the paper the research would also preclude such analysis on vintage fortified wines such as Port and Madeira, which include base alcohol not necessarily matching the area or vintage of the wine, and Champagne equivalents (even vintage) as they contain both extra sugar for the secondary fermentation and the syrupy dosage used after disgorgement. Sherry would be doubly useless, as it is both fortified and subject to a Solera system that means the (average) vintage age of even the oldest Solera level is only 15 years.
My own scientific curiosity was piqued by the comments on the massive increase of atmospheric 14C following the nuclear tests of the 1950s and 60’s. I was also interested by some of the reasons to explain where exceptions were expected and why – such as wine produced near to nuclear power stations, which produce CO2 with more 14C than normal, the opposite of coal, oil and gas-fired plants. This excludes several wine areas from the research, including most of the Côtes du Rhône. Wines from Portugal were also atypical, likely due to different CO2 exchange effects due to proximity to the ocean which could not be calibrated for by the background 14C data used on the other continental wine regions. These sorts of factors lend themselves to future research projects to create new modelling and calibration techniques on these areas.
Many thanks to Professor Meijer for forwarding the article and images to me, and for his comments.