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Terroir provides stress, and that you can taste!

The terroir of wine, who has not heard of it? Wine experts often shed their light on the terroir in almost poetic language. But what do they taste, and can this really be traced to the grapevine in the field, not on the left, but on the right side of the road?

Terroir is a collective term for everything that affects the grapes in the vineyard. The terroir is therefore derived from the soil, the location and vegetation of the vineyard, the (micro) climate, but also the actions of the winegrower in the vineyard1. The term terroir implies that the wine has unique characteristics that cannot be duplicated in another location, despite the use of the same grape varieties and vinification methods. Is it true that the direction of the rows in the vineyard, the defoliation, the thinning of the bunches, those cool breezes compared to the valley further down, or a lime or clay soil make so much difference to the aromas of the wine?

Terroir is composed of the factors soil, climate, location and vineyard management
Terroir is composed of the factors soil, climate, location and vineyard management

The influence of terroir on the grapevine

Any external influence on the vine, both biotic (attack by birds, parasites, bacteria, fungi, weeds, etc.) and abiotic (differences in temperature, drought, sunlight, soil composition, etc.) causes stress. To protect its integrity, the vine will adapt to these stressors. The adjustments in the vine as a result of all these influences (the terroir) can already take place at the level of the DNA. DNA codes for proteins, the regulatory substances in every cell. A piece of DNA that codes for a protein is called a gene. These genes can be “switched on or off” under the influence of a stressor. This is done by removing or placing so-called methyl groups – a carbon atom with three bonded hydrogen atoms – on the DNA2, 3. These methyl groups can block access to a specific gene so that it cannot be used, and cannot be translated into an active protein (Figure 1). About 5% of all genes on the DNA can be switched on or off by the influence of the terroir4. Five percent may seem small, but since a large proportion of these genes code for transcription factors4 – these are proteins that produce other proteins – it can nevertheless have a huge effect on the molecular processes in the grapevine.

In the Barossa Valley in South Australia, they looked at the methyl groups on the DNA of Shiraz vines in 22 different vineyards. It was possible to group the vineyards based on their location by using their DNA methylation. The researcher found that approximately 24% of the variation in methylation was dependent on the latitude of the vineyard. More remarkable, however, is that the height of the vineyard and even the guiding method used (cordon or guyot) influence the placement of the methyl groups on the DNA of the vines2.

DNA Methylation is changes under influence of stress
Figure 1. Stress changes the methylation of DNA

The effect of terroir on wine

It is nice to see that the DNA becomes slightly more or less accessible through the placement of methyl groups, but does this actually have an effect on the aromas of the wine? Yes it does! A gene must be accessible to be read by the machinery that produces proteins. This ‘expression of the genes’, the extent to which they are read to produce proteins – has a direct link with terroir-specific aromas in the wine3, 5, 6.
A good example of the effect of terroir on the aromas in wine is the regulation of abscisic acid in the grapevine. The genes that regulate the production of abscisic acid are very sensitive to the influences of terroir7. Abscisic acid is a hormone that regulates the growth and development of the vine, but also the (stress) response of the vine to (a)biotic stressors such as mechanical damage, fungi, bacteria, weeds, drought, cold, heat, etc.8. By doing so, abscisic acid affects the amount of anthocyanins and flavonols that are present in the grape9. The effects of the terroir on the regulation of abscisic acid have therefore directly an effect on the aromas in the wine.

The actions of the winegrower in the vineyard can – just like the climate, the location and the soil – cause a (stress) reaction of the vine. Whether this always ensures that the DNA of the vine is methylated differently is not known. However, it is not unlikely given the effect of the type of guiding method (i.e. cordon or guyot) on methylation2. It is however certain that the actions of the winegrower have an effect on the composition of the aromas in the wine. Vineyard management such as the orientation of the rows10, pruning11, cluster zone leaf removal12-14, cluster thinning15, water management11 and of course a low yield16 have influence on the flavor profile and quality of the wine. Water management and the yield (the number of hectoliters of wine per hectare) are known to have an influence on the expression of terroir11, 16. For the other factors of vineyard management it is reported that they can improve the quality of the wine. The question is whether the quality of wine is synonymous with terroir expression in wine. Nevertheless, phenolic ripeness –the optimal aromatic ripeness of the grape – is an important factor for terroir expression16. The “terroir effect” only arises during grape ripening. Terroir-specific stilbenes and anthocyanins only then concentrate in the grape. In unripe grapes picked before the véraison, no effect of the terroir on the composition of the grape can be demonstrated6. Harvesting phenolic unripe grapes therefore ensures that the terroir expression in the grapes is reduced. Vineyard management that influences the ripening of the grapes (e.g. through defoliation, green harvest, cluster thinning, yield reduction, etc. ) can therefore have an effect on the expression of terroir.

In short, the winegrower controls the microclimate of the grapevine and as such regulates the stressors that affect the grapevine. For example, defoliation of the cluster zone results in extra sunlight on the clusters. To protect the grape against this extra UV radiation, extra flavonoids are produced in the skins of the grapes17. These flavonoids serve as pigments – a natural sunscreen – in the skin, but also add extra color and taste to the wine. And that is exactly what the winegrower had in mind.

Vintage vs. terroir effect

The vintage effect – the effect of a good or bad summer – is many times greater than the effect of terroir18. This is simply because the effect of a wet summer on the growth and ripening of the grapes is much greater than the subtle differences in terroir expression. The terroir effect is therefore (sometimes literally) snowed under by the vintage effect. However, Burgundy wines that only showed a noticeable vintage effect when bottled developed a different chemical composition after a few years in the bottle that could be traced to the specific vineyards where they came from. These wines therefore “remember” their origin in the form of the composition of part of their metabolites19. Furthermore, by using statistical methods on the complete dataset of aromatic substances of a wine, it is possible to filter out the vintage effect and observe terroir-specific differences5, 6. A strong vintage effect, or a bad wine year, does therefore not necessarily mean that there is no terroir expression.

Terroir expression and bluff poker

Terroir expression can be demonstrated scientifically in wine.  That is, factors such as latitude, guiding method, soil, row orientation, pruning methods, defoliation, water management, low yield, and other forms of vineyard management have a measurable influence on the aroma profile and the terroir expression of the wine. The terroir is a sum of all these factors, and it will be extremely difficult, if not impossible, to distinguish a single variable – such as the latitude of the vineyard or the precise orientation of the rows – by tasting the wine. Moreover, if certain terroir-specific aromas reach the (theoretical) perception threshold it always remains the question whether the wine drinker has developed such a taste palette to recognize the aromas. What a scientist can measure is not necessarily something that a wine drinker can taste. For trained tasters it may be possible to recognize and interpret a number of terroir-specific elements, but for the common foot folk a good bit of bluff poker may come in handy.

References

1.  Organisation Internationale de la Vigne et du Vin. Resolution OIV/VITI 333/2010. In: Castellucci F, editor. General Assembly Tbilisi 2010.
2.   Xie H, Konate M, Sai N, Tesfamicael KG, Cavagnaro T, Gilliham M, et al. Global DNA Methylation Patterns Can Play a Role in Defining Terroir in Grapevine (Vitis vinifera cv. Shiraz). Frontiers in plant science. 2017;8:1860.
3.   Fortes AM, Gallusci P. Plant Stress Responses and Phenotypic Plasticity in the Epigenomics Era: Perspectives on the Grapevine Scenario, a Model for Perennial Crop Plants. Frontiers in plant science. 2017;8:82.
4.   Dal Santo S, Tornielli GB, Zenoni S, Fasoli M, Farina L, Anesi A, et al. The plasticity of the grapevine berry transcriptome. Genome biology. 2013;14(6):r54.
5.   Anesi A, Stocchero M, Dal Santo S, Commisso M, Zenoni S, Ceoldo S, et al. Towards a scientific interpretation of the terroir concept: plasticity of the grape berry metabolome. BMC plant biology. 2015;15:191.
6.   Dal Santo S, Commisso M, D’Inca E, Anesi A, Stocchero M, Zenoni S, et al. The Terroir Concept Interpreted through Grape Berry Metabolomics and Transcriptomics. Journal of visualized experiments : JoVE. 2016(116).
7.   Sun R, He F, Lan Y, Xing R, Liu R, Pan Q, et al. Transcriptome comparison of Cabernet Sauvignon grape berries from two regions with distinct climate. Journal of plant physiology. 2015;178:43-54.
8.   Cutler SR, Rodriguez PL, Finkelstein RR, Abrams SR. Abscisic acid: emergence of a core signaling network. Annual review of plant biology. 2010;61:651-79.
9.   Koyama K, Sadamatsu K, Goto-Yamamoto N. Abscisic acid stimulated ripening and gene expression in berry skins of the Cabernet Sauvignon grape. Functional & integrative genomics. 2010;10(3):367-81.
10.   Hunter JJ, Volschenk CG. Chemical composition and sensory properties of non-wooded and wooded Shiraz (Vitis vinifera L.) wine as affected by vineyard row orientation and grape ripeness level. Journal of the science of food and agriculture. 2018;98(7):2689-704.
11.   Pascual M, Romero MP, Rufat J, Villar JM. Canopy management in rainfed vineyards (cv. Tempranillo) for optimising water use and enhancing wine quality. Journal of the science of food and agriculture. 2015;95(15):3067-76.
12.   Sternad Lemut M, Sivilotti P, Franceschi P, Wehrens R, Vrhovsek U. Use of metabolic profiling to study grape skin polyphenol behavior as a result of canopy microclimate manipulation in a ‘Pinot noir’ vineyard. Journal of agricultural and food chemistry. 2013;61(37):8976-86.
13.   Moreno D, Valdes E, Uriarte D, Gamero E, Talaverano I, Vilanova M. Early leaf removal applied in warm climatic conditions: Impact on Tempranillo wine volatiles. Food research international (Ottawa, Ont). 2017;98:50-8.
14.   Zhang P, Wu X, Needs S, Liu D, Fuentes S, Howell K. The Influence of Apical and Basal Defoliation on the Canopy Structure and Biochemical Composition of Vitis vinifera cv. Shiraz Grapes and Wine. Frontiers in chemistry. 2017;5:48.
15.   Rutan TE, Herbst-Johnstone M, Kilmartin PA. Effect of Cluster Thinning Vitis vinifera cv. Pinot Noir on Wine Volatile and Phenolic Composition. Journal of agricultural and food chemistry. 2018.
16.   Van Leeuwen C. Chapter 9 – Terroir: the effect of the physical environment on vine growth, grape ripening and wine sensory attributes. In: Reynolds AG, editor. Managing Wine Quality. Series in Food Science, Technology and Nutrition: Woodhead Publishing; 2010. p. 273-315.
17.   du Plessis K, Young PR, Eyeghe-Bickong HA, Vivier MA. The Transcriptional Responses and Metabolic Consequences of Acclimation to Elevated Light Exposure in Grapevine Berries. Frontiers in plant science. 2017;8:1261.
18.   Roullier-Gall C, Lucio M, Noret L, Schmitt-Kopplin P, Gougeon RD. How subtle is the “terroir” effect? Chemistry-related signatures of two “climats de Bourgogne”. PloS one. 2014;9(5):e97615.
19.   Roullier-Gall C, Boutegrabet L, Gougeon RD, Schmitt-Kopplin P. A grape and wine chemodiversity comparison of different appellations in Burgundy: vintage vs terroir effects. Food chemistry. 2014;152:100-7.

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1 Comment

  1. Jonathan Rodwell

    Very interesting to read of these advances in appreciating and deciphering transcriptional genetic response. Hopefully this starts to take us closer to the relative order of magnitude of all the relative terroir components and those perhaps which are unique.

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