Tackling the 2019 MW Exam Part 2: Discuss the role of the following factors in the production of high-quality grapes: aspect, vine density and row orientation

It is often said that one can produce bad wine from good grapes but cannot produce good wine from bad grapes. There is little room, if any, for debate when it comes to the importance of viticultural decision-making in producing high-quality wine. From the very beginning of a vines life the decisions taken in the vineyard, from planting to clonal selection, will go some way toward determining the quality of the finished wine. Factors often principally touted amongst fact sheets are aspect (direction) vine density and row orientation. But exactly what role do these factors play when it comes to producing high-quality grapes …

Defining high-quality grapes is somewhat more ‘simplistic’ and objective when compared to defining high-quality wine. Individual preference, a fundamentally subjective metric, is often overwhelmingly confounding in the latter. Of course, it is possible to taste for structural balance, but broadly speaking the definition is not one which is easily measured. However, in viticultural terms, both physiological and sugar ripeness can be objectively measured (physiological with a somewhat more experimental nature) They can be measured alongside other observable and measurable factors (such as the presence of disease and infection) and together constitute what can be more commonly agreed upon as a definition of high-quality grapes.

That being said, exactly what role does aspect, vine density and row orientation play in producing high-quality grapes.

Aspect more commonly refers to the compass direction in which a particular site faces, the importance of aspect is evident in its dialectic prevalence. Winemakers tout it, fact sheets display it and tasters use it to form quality expectations. Due to the position of the Earth in relation to the Sun, north-facing slopes in the northern hemisphere receive less direct sunlight than south-facing slopes, thus they are cooler, the reverse is true in the southern hemisphere. Furthermore, regardless of hemispheric positioning, the sun rises in the east and sets in the west, as the day progresses the rotation of the Earth brings the sun more directly above any particular site and overall temperature and intensity are increased. The result is that those sites positioned south-east receive gentle morning sun and avoid the intense midday heat whereas those facing south-west experience more intense sunlight and warmth throughout the afternoon.

Having already established that aspect has a considerable impact upon the exposure of a site to sunlight and warmth, we may now ask ourselves exactly what role this exposure plays in the production of high-quality grapes?

Throughout the growing cycle, but more particularly during the period of veraison, grapes progressively ripen. This ripening fundamentally owes itself to photosynthesis. As grapes ripen, the concentration of sugars build-up and concentration of acids decreases, in part due to simple dilution but also as a result of plant respiration. During this period of ripening, the concentration of flavour compounds begin to build up (primarily in the skins) anthocyanins replace chlorophyll, tannins ripen, mineral content changes and total acidity and pH shift. In order to produce high-quality grapes, this ripening period should ideally be balanced, of suitable length (not rushed by excessive sunlight/warmth) and be well-suited to the variety.

High-quality grapes will more commonly be produced on sites that possess an aspect suiting both the varietal and regional weather and/or climate. Cabernet Sauvignon, for example, is a fairly late-ripening variety, it also shows vast variation in flavour profile dependant on how completely it has ripened. In a particularly warm region, Cabernet grown on a south-west-facing slope may show a stewed, jammy flavour profile and possess a level of total acidity too low to provide structure, longevity and freshness. Conversely, in a region with a cooler climate, Cabernet grown on a north-facing slope may struggle to ripen and may also exhibit green, vegetal notes due to higher levels of pyrazines (of which the concentration is reduced with increased sunlight exposure)

Similarly, in the Mosel valley, where the climate is cold and temperate, the Riesling grape can struggle to ripen even in ‘good vintages’ Here, a south-west facing slope maximises exposure to sun and warmth throughout the day, increasing the likelihood of a more consistent, extended and complete ripening period where acidity is able to reach more balanced and palatable levels.

As with Cabernet, flavour compounds in Riesling grapes have been shown to vary greatly dependant upon sun exposure. Gerdes et al. 2002 have shown that concentrations of TDN ( the compound associated with a petrol aroma) increase with sunlight exposure above a threshold of about 20%. Further studies have outlined the importance of sun exposure in adjusting levels of aroma compounds in grapes. Furthermore, Bureau et al. 2000 have shown that Syrah bunches shaded by 90% shade cloth had lower levels of monoterpenes and C13-norisoprenoids, whilst Belancic et al. 1997 has shown that in Muscat the highest concentration of free terpenes was found in the artificially semi-shaded (50%) treatment.

Additionally, the morning sun experienced by east-facing vineyards is advantageous in reducing disease pressure and limiting frost damage. Vines grown on eastern slopes are able to dry off sooner than those on a western slope, thus reducing disease risk which may be heightened by extended periods of damp. This morning sun and increased warmth experienced by south, and south-east-facing slopes, also assist the melting of both snow and frost, both are particularly crucial during bud burst.

Row orientation refers to the direction in which rows of vines are planted, possible options are NS, EW, NE-SW, and NW-SE. Depending on the orientation of the row, the angle of incidence of the sun may affect light and temperature profiles in the rows, as well as inside the canopies. Sunlight exposure and temperature are well-known regulating drivers of modification of whole plant and berry size and the wide variety of biochemical and physiological processes taking place pre and post-véraison in both canopy and grapes.

The oenological quality potential of grapes is largely determined by these two environmental factors. They are linked to sugar accumulation, anthocyanin formation, flavonol and tannin contents, and terpene, carotenoid and methoxypyrazine synthesis.

Hunter J.J. et al. have shown that EW-orientated rows show the lowest interior canopy solar interception. The NS orientation displayed the highest values, whereas NE-SW and NW-SE orientations showed the highest peaks in the afternoon and morning, respectively. Fundamentally their work has shown that in order to gain the most benefit in yield and grape quality from row orientation as a complimentary viticulture practice, decisions should be carefully considered in respect of the dominant terroir and desired style.

Hunter J.J. et al. have further shown that inter-row wind, canopy physiology, vine growth and yield are also affected by row orientation.

Their detailed study has shown that incoming wind velocity can be tempered by decisions made relating to row orientation. Subsequently, the proper selection of row orientation may decrease disease pressure. In addition, uniform canopy photosynthesis (relating to canopy physiology) was shown to be exhibited for NS and NW-SE orientations. Rows facing W, S, SE, and SW displayed lower average photosynthesis and photosynthetic efficiency. The result of this is that yields of NS orientated rows were higher and more consistent in the particular terroir observed.

It appears evident that row orientation as a viticulture practice is of significant importance in the pursuit of grape and wine quality/style. Row orientation choices should be carefully considered in order to obtain favourable compromises between vegetative growth, inflorescence development, berry development, grape exposure and impacting microclimatic factors affected by viticulture practices.

Finally, vine density. Vine density is a measure of how closely spaced vines are in the vineyard, both within the row and between rows. In Burgundy, Bordeaux and Champagne a standard density tends to be around 10,000 vines/ha whereas in Santorini it can be as low as 2,500/ha and in some experimental vineyards elsewhere as high as 40,000/ha. There is little evidence to suggest that there is a universal rule relating to high-quality grapes (i.e low density equals high quality) nor that vine vigour is directly managed by density alone. The case seems to be that vine density is instead somewhat informed, and decided upon, by the perceived vigour of any given site when making initial vineyard decisions.

Traditionally it has been said that high vine densities tend to lead to improved wine quality, this notion has perhaps emerged due to correlation (correlation does not equal causation) between high-density planting in the Old World. It is however difficult to make an evidence-based argument for high-density planting being a prerequisite to producing high-quality grapes. In the new world, numerous vigneron have opted for high-density planting in sites perceived to have good soil potential; however, this has rarely resulted in an emulation of the high-quality wines of the new world, it has instead resulted in excessively vigorous vineyards with canopies so extensive that excessive shading is noted, thus reducing quantity. It is in fact the experience of several New World vigneron that once they have reduced vine density an increase in grape quality quickly follows.

In Europe, both research and commercial experience of the vigneron have indicated the high-density planting employed in much of the old world is in fact preferentially suited to vineyards with low soil potential (like those of much of the New World) Assumedly the logic here would be that the vines are forced to ‘battle’ for resource more effectively opposed to an irrigated vineyard with high soil potential where the vines simply flourish regardless of vine density. There is likely a connection to be made between this excessive vigour in high-density/high soil potential sites and features commonly associated with poor quality such as increased shading, reduced intra-row wind flow and yield; however, it is likely that this is more closely linked to canopy management. It could be said that actually a balance of soil understanding and overall management (open canopies and an appropriate ratio between fruiting and vegetative growth) is really what can result in high-quality grapes.

It is a fairly widely-held opinion that mild water stress is desirable for optimum wine quality. There is, however, almost universal agreement that water deficit should be sufficient before veraisonto stop shoot tips actively growing and attracting assimilates away from the ripening fruit, to the detriment of wine quality. Stephen Skelton MW states that in non-irrigated vineyards the same amount of water is available whether there are 1,000 or 10,000 vines per ha therefore the higher the density the less water each vine has available to it. He further states than when coupled with the right rootstock, higher density wins every time.

There appears to be little place for argument against the belief that aspect, vine density and row orientation play a critical role in the production of high-quality grapes; however, it appears most important to view these viticultural factors as pieces of the puzzle, or tools in the boxes, opposed to independent variables with universally applicable rules. The impact of these factors vary dependant on region, terroir, desired style and variety and as such it is the role of the vigneron to understand the varying implications of each of the aforementioned and make decisions accordingly to support case-by-case requirements.

5 thoughts on “Tackling the 2019 MW Exam Part 2: Discuss the role of the following factors in the production of high-quality grapes: aspect, vine density and row orientation

  1. You state “So if a relationship were to exist in a particular vineyard between planting density and water availability”. In non-irrigated vineyards the same amount of water (and nutrients) are available whether there are 1,000 or 10,000 vines per hectare therefore the higher the density the less water each vine has. Couple this with the right rootstock and higher density wins every time. Higher density also means each vine has less grapes to ripen (for any given yield) which results in riper grapes. In warm/hot climates where irrigation is used/needed things are different although many new world regions start out with wide rows and low densities but move to narrower rows and higher densities over time.

    Liked by 1 person

    1. Thanks for the feedback again Stephen, regards the first point I think I have perhaps not made myself clear, I agree with you, in these given scenarios high-density planting wins. I will add an edit as I did based on your previous feedback, thank you again.

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