Trellising systems are driving the mechanisms that alter canopy microclimates, consequently affecting yield and quality of grapes.
Viticulture practices affecting grape and wine composition
In the vineyard, the bunch zone environment is variable due to uneven light distribution in the canopy. The vineyard row orientation and the architecture of the vine can determine the amount of light intercepted and distributed around the canopy. All this has a direct impact on photosynthetic capacity and vegetative and reproductive growth.
Several ways of managing vine growth and optimising yield by increasing photosynthesis active reactions, can be achieved by modification or manipulation of the canopy. The strategies used can either target a specific developmental stage, for example at berry set, véraison or harvest, or can be done on a long-term basis such as establishing a suitable permanent vine architecture or converting it only when necessary. However, both strategies come with drawbacks, so it is essential for the winegrower or winemaker to make the initial correct decisions regarding the type of techniques that can maximise yield while maintaining quality.
When canopy density increases, it can negatively affect the grapevine microclimate. To avoid this situation, canopy management actions are implemented to bring vines’ vegetative and fruiting performance in balance by reducing shoot length, leaf density, and number of clusters per vine. Those techniques eventually improve light in the canopy environment, and a key requirement in fruitiness and vegetative growth.
Pioneer studies have illustrated that the application of seasonal practices have a great impact on grape and wine composition.1 For example, components such as total soluble solids increase when partial defoliation is practiced; at the same time, this practice can reduce TA in the fruit depending on the cultivar. In addition to basic oenological parameters, other components such as odour and flavour molecules are affected by alteration of the canopy environment, for example on compounds sensitive to light.
The timing of seasonal practices is of utmost importance, as this can affect the synthesis and accumulation of certain compounds, improve grape composition, control yield, etcetera. Leaf removal can also have positive results on Botrytis incidence reduction.
When it comes to permanent structures, different trellising systems create their own micro-climatic conditions noted in differences in air movement, bunch temperature and air temperature around canopies. The conditions created can be linked to effects in the vegetative growth, grape composition, and wine composition and quality, but also water usage as trellis type can influence the transpiration. Grapevines on a horizontal trellis have higher transpiration rates than those on vertical trellises. Another benefit of trellising vines is the significant role they have on yield, although results are site- and cultivar-dependent.
Effects of trellising systems on shade and light
Canopy division promotes increases in yield and quality,2 and improvement of training systems overcome canopy shading. Canopy shade is a common problem in vineyards which can cause reductions in vineyard yield and wine grape quality. In grapevine canopies, depending on architecture, foliage and fruit berries can develop in conditions varying from shaded through to fully exposed (open). In general, berries developed from open canopy conditions have higher juice sugar concentration, improved acid balance, less unripe herbaceous fruit characters and berry phenolics concentration increases including anthocyanins in red varieties as opposed to shaded canopy conditions.3 Shaded canopies entail trellising systems such a Santorini and Stok-by-paaltjie, whereas open canopies include systems such as Ballerina and Smart Dyson (vertically divided), T-frame and Lyre (horizontally divided) canopies.
Effect of trellising system on grape and must composition
Trellis effect on yield
Trellis improves the canopy microclimate and leads to improvement in yield and quality, because of better leaf and fruit exposure to sunlight. As vine density can differ according to the planting, mass of grapes per vine is sometimes used in the scientific literature as opposed to mass per vineyard surface, more used in practice. Canopy division is an effective vehicle for accommodating high vine vigour by enhancing leaf and fruit microclimate, although results are site- and cultivar-dependent. For most of the cultivars, horizontally divided canopies have positive effects on yield as they increase shoots exposure and improve bud fruitfulness due to good sunlight penetration.
Vine architecture that can support a larger canopy can ensure proper light exposure which may produce quality grapes and therefore wines. However, this may not always be the case, as other factors may play a role.
Trellis effect on grape and must composition
Generally, berries maturing in densely shaded canopy interiors are generally associated with low total soluble solids, high titratable acidity, and low pH among others when compared with berries in open or exposed canopies. Solar irradiation affects the levels and pattern of sugar accumulation, organic acids, and amino acids across grape clusters; for example, increasing sunlight exposure is associated with lower accumulation of organic acids.
Effect of trellising systems on wine composition
Light has been shown to affect the accumulation of aroma precursors, volatile compounds, and phenol free glycosides and, as a consequence, affect the chemical and sensory properties of wine.
Only few investigations have been done in the South African environment and its climate, especially on white varieties and more specifically Chenin blanc. Nevertheless, the findings of Van Zyl and Van Huyssteen (1980), demonstrated a significant effect of trellising on Chenin blanc grapes composition,4 and Volschenk and Hunter (2001), found a significant impact on grape composition mostly on aroma and flavour descriptors1 even though not on the wine quality. The evaluation (chemistry or sensory) of wines made from different trellising systems has been included in very few studies and only the overall wine quality was evaluated. Van Zyl and Van Huyssteen (1980), found differences in ratings between Chenin blanc wines of different systems mainly due to colour.4 The literature suggests that divided canopy trellis produce better wines due to better light interception.5 In contrast, other authors did not find a significant effect on Chenin blanc wine quality for trellis systems which have been converted.1
Despite the work done for grapes, not much has been investigated on trellising systems’ effects on wine composition. Usually, studies have included many variables due to the variability of the blocks included in the work. Factors such as vineyard location can influence mesoclimate and macroclimate, even when the same cultivar is investigated. Other factors such as vine age, clone, soil composition, row orientation, etcetera can complicate the interpretation of the results.
In 2017 and 2018, we had the opportunity to work in a Chenin blanc model block containing six different trellis systems, planted all at the same time. The study covered limited viticultural aspects, but focused rather on the comprehensive profiling of the resulting wines. The results will be presented in the next two parts of the series, dedicated to chemistry and sensory aspects of aroma, taste, mouthfeel, and wine quality.
The desired wine characters start with berry composition in addition to winemaking and ageing process.
Grape composition plays a significant role in defining wine style and typicality and there are ways in which grape composition can be altered or modified. Among these ways are viticultural practices – including trellising systems.
- Volschenk, C.G. & Hunter, J.J., 2001. Effect of trellis conversion on the performance of Chenin blanc/99 Richter grapevines. South African Journal of Enology and Viticulture 22: 31 – 35.
- Shaulis, N.J., Amberg, H. & Crowe, D., 1966. Response of Concord grapes to light, exposure, and Geneva Double Curtain training. Proceedings of the American Society for Horticultural Science 89: 268 – 280.
- Gladstones, J., 1992. Viticulture and environment : A study of the effects of environment on grapegrowing and wine qualities, with emphasis on present and future areas for growing winegrapes in Australia. Adelaide: Winetitles.
- Van Zyl, J.L. & Van Huyssteen, L., 1980. Comparative studies on wine grapes on different trellising systems (Part 2): Micro-climatic studies, grape composition and wine quality. South African Journal of Enology and Viticulture 1: 15 – 25.
- Reynolds, A.G. & Vanden Heuvel, J.E., 2009. Influence of grapevine training systems on vine growth and fruit composition: A review. American Journal of Enology and Viticulture 60: 251 – 268.
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