FOOD & AGRICULTURE


developments in the near future.2


Apart from the advancing


harvest dates, the temperature increases have also changed grape composition, driving up alcohol levels by up to two percentage points and increasing the pH by 0.2 units. As with the harvest dates, the


first, moderate changes in this direction were often welcome as they improved the quality of the wine. However, higher temperatures are soon projected to drive these parameters away from the optimum, making it more and more difficult to produce good quality wines. Even the taste of a specific wine


can be altered by temperature changes. Thus, the concentration of various aroma chemicals such as 3-isobutyl-2-methoxypyrazine (IBMP, responsible for a bell- pepper aroma) or rotundone (a sesquiterpene also found in pepper and other spices) are known to decrease with a rise in temperature. On the other hand, 1,1,6-trimethyl- 1,2-dihydronaphthalene (TDN), known to develop in ageing Riesling wines and produce petroleum flavours only appreciated by the more adventurous connoisseurs, has long been known to increase with higher temperatures during the ripening phase. Terpene alcohols have been reported to respond in various ways, increasing, decreasing or remaining unaffected. These changes may


make the wine better, worse, or just different, but in a market where consumers are used to associating the name of a village or mountainside with a very specific taste experience, any change to the established link between terroir, grape, and the taste and quality of the wine is certain to upset a well- established business. It is clear


that much


of the planetary surface is getting warmer, but changes in precipitation are much harder to predict. As climate change disrupts established hydrological regimes, some places will get drier, others wetter. Both ‘unprecedented’ floods and catastrophic droughts are among the hazards of climate change some parts of the world are already experiencing that won’t go away. Van Leeuwen and Darriet


modelled water balance in the Bordeaux region using a published model. They find that vineyards have become dryer between 1952 and 2012, although this is in part due to rising temperatures and increasing evapotranspiration. Grapevines are fairly drought-resistant, and in many parts of Europe a relatively dry year is generally considered a good year. As with other parameters, this only works to a certain extent, before the plants actually begin to suffer from the drought. Changes in precipitation are also


likely to involve extreme weather events, including torrential rain and hailstorms, both of which can damage crops. The south of France has seen an increasing frequency of such events, which have already caused damage. A third changing parameter over


the past few decades is the exposure of vines to UV-B radiation. In the right amounts, this part of sunlight creates desirable flavour compounds in grapes, but excess UV-B can produce off-flavours in white wines and even ‘sunburn’. The risks of radiation exposure limit the extent to which growers can move to higher altitudes to escape increasing temperatures.


Adapt or move? Climate change affects wine growers around the world, in Chile and Australia as much as in Europe and California. A recent conference on wine growing under climate change held in Bordeaux3


had contributions


from 20 different countries, including studies of the challenges growers face in Portugal4


and China.5


The only reason why France and other traditional European wine growing regions have more to worry about than relative newcomers like Australia


lies in the tight connection between the established labels, the terroir they grow on, and the grape varieties used. This combination optimised for the climate of the past four centuries will no longer work in the 21st century. Any changes to the recipe, however, are bound to cause trouble with the hard-fought recognition of labels like ‘appellation controlee,’ and with customers. So what could be changed? Short of pulling up Pinot Noir vines in Champagne and replanting them in Dorset, van Leeuwen has a few suggestions of adaptive measures that wine growers can make in situ.6 To stop the harvest time from


moving further away from the ideal timeframe, which in the northern hemisphere starts in early September, growers could change their viticultural techniques and/or their plant material to delay ripening of the grapes. For instance, growers could add


a few days to the ripening cycle by delaying the spring pruning, or by allowing the vines to grow higher above the ground, where the air is slightly cooler than just above the soil. While these changes are benign, other measures, such as reducing the leaf area, may have complex consequences that could interfere with the quality of the wine. In selecting the plant material,


growers could reverse the trends of the 20th century, when it made sense to select rapidly ripening varieties. Simply by adapting the choice of variety from among the range of varieties already used in a given region to the changing climate, growers can to some extent mitigate the anticipated effects. Van Leeuwen believes relatively


conservative measures compatible with keeping the established regional styles may keep wine growers in business until 2050. However, he writes6


: ‘In the second part of the 21st


century, more invasive adaptations, like severe reductions in leaf area to fruit weight ratio, or the introduction of non-local, later ripening varieties will, most likely, be unavoidable.’ Alternatively, wines may by then


have started to migrate towards the poles. Wines now coming from California may be produced in Washington State, and the premium fizz we now call Champagne may be known as Devon or Kent.


5.3m


Average number of bottles of English wine produced annually in recent years, up from 1500 bottles/year 50 years ago


Temperature changes can affect the taste of a specific wine, for example, by affecting the concentration of aroma chemicals such as IBMP, responsible for a bell-pepper aroma, or rotundone – a sesquiterpene also found in pepper and other spices


References 1 B. I. Cook and E. M. Wolkovich, Nature Climate Change, 2016, 6, 715.


2 C. van Leeuwen and P. Darriet, J. Wine Econom., 2016, 11, 150.


3 N. Ollat et al., OenoOne, 2017, 51, 59.


4 H. Fraga et al., OenoOne, 2017, 51, 61.


5 Y. Li, I. Bardaji, OenoOne, 2017, 51, 71.


6 C. van Leeuwen and A. Destrac-Irvine, OenoOne, 2017, 51, 147.


09 | 2017 25


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52