WINETECH Technical Yearbook 2021

Vine nitrogen status as soil component Vine nitrogen status is a major driver of aroma compounds in grapes and wine, with a high nitrogen status often increasing IBMP in Sauvignon blanc, Cabernet Sauvignon and Merlot. Volatile thiol precursors increase with nitrogen status, with volatile thiols being particularly important in Sauvignon blanc, Cabernet Sauvignon and Riesling. Excessive N-status can cause undesirably high levels of green aromas in Cabernet Sauvignon and high N-status causing lower TDN levels in Riesling. Vine water status as affected by soil and climate Vine water status is an important driver of wine typicity and depends on climate (for example rainfall) and soil type. Vines exposed to water deficit yield wines with less green aromas (Cabernet Sauvignon, Mer lot and Sauvignon blanc) and (-)-rotundone (Syrah). These wines are also fruitier, contain more C 13 -norisoprenoids and, after bottle ageing, contain more DMS and show improved ageing bouquet. Riesling wine from vines under water deficit is more likely to develop AAP (paint- like, mothball and medicinal aromas). Prediction of aroma expression from various terroirs Terroir expression is mainly driven by

air temperature, radiation, vine water status and vine nitrogen status. Following measurement and characterisation of these terroir factors, aroma expression can be predicted by using published data. Note that the interplay between environmental conditions, plant material, viticulture management and winemaking practices is complex and needs more research. Terroir factors (for example vine water and nitrogen status) are also often not clearly separated. Examples of typical aroma expression from specific terroirs Cool climate Sauvignon blanc, as grown in Marlborough (New Zealand) and Sancerre (France), typically shows a fine balance between green and fruity aromas. The Awatere Valley (New Zealand), with a very cool climate, produces Sauvignon blanc with dominant bell pepper and asparagus aromas. Warm climate Sauvignon blanc, found in the USA, Australia and Chile, is dominated by passion fruit aromas. Merlot and Cabernet Sauvignon from cool climates can be green, whereas Merlot and Cabernet Sauvignon from temperate climates show fruity aromas, with a complex ageing bouquet the result of a couple of years of bottle ageing. Syrah from cool climate terroirs, such as the northern Rhone Valley (France), Victoria’s Grampians region (Australia) or Hawke’s Bay area (New

Zealand), shows very peppery aromas, caused by (-)-rotundone. Managing aroma expression of a specific terroir The link between terroir and the expression of specific aroma is clear. The choice of plant material and management practices can, however, influence this expression. For instance, the presence of unwanted green aromas in red wine can be reduced by planting Merlot, an early ripening varietal, instead of Cabernet Sauvignon. Other options include the planting of cover crops to reduce nitrogen or leaf removal, which increases light exposure and bunch zone temperature. Warm climate red wines tend to show excessive dried fruit aromas. This can be reduced by planting Cabernet Sauvignon, a later ripening varietal. Other options include earlier harvesting and increased vigour, which cause less sunlight exposure of bunches. Grapefruit aroma in Sauvignon blanc can be increased by nitrogen fertilisation if nitrogen is a limiting factor. Winemaking impact Fermentation and ageing are vital in aromatic expression. Fermentation releases or forms aromatic compounds, such as β-damascenone, β-ionone, volatile thiols, esters and monoterpenes. And ageing might increase compounds such as tabanones

(tobacco aroma). Yet, other aromatic compounds, such as volatile thiols, can be lost during pre-fermentation processing or decline during ageing as is the case with linear fatty acids. The role of winemaking technique is not to be underestimated in aroma expression. CONCLUSION The effect of terroir is key in aroma expression in wine. By better understanding the link between a specific site and wine typicity, informed decisions can be made to improve wine quality. More research is however needed, wi th improved experimental design, to better understand individual terroir effects on vines and ultimately more accurately predict and manage aroma typicity in wine. REFERENCE Van Leeuwen, C., Barbe, J., Darriet, P., Geffroy, O., Gomès, E., Guillaumie, S., Helwi, P., Laboyrie, J., Lytra, G., Le Menn, N., Marchand, S., Picard, M., Pons, A., Schüttler, A. & Thibon, C., 2020. Recent advancements in understanding the terroir effect on aromas in grapes and wines. OENO One 4, 985-1006.

For more information, contact Bernard Mocke at bmocke@gmail.com.

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