Abstract
Under the effects of climate change, it is becoming increasingly common to observe excessively fast grape sugar accumulation while phenolic and flavour development are lagging behind. The aim of this research was to quantify the impacts of three different leaf removal techniques on the canopy architecture and ripening of Cabernet Sauvignon trained in a sprawl trellis system. Treatments were performed at veraison (~14 °Brix) and included (i) control; (ii) leaf plucking in the bunch zone; (iii) leaf plucking the top two-thirds of shoots, apical to the bunches; and (iv) shoot trimming. On the date of harvest, no significant difference in total soluble solids was observed between treatments. Other results including the effect of the treatments on fruit acidity, anthocyanins, phenolics, and tannins were somewhat inconclusive. While various other studies have shown the potential of leaf removal to achieve slower grape sugar accumulation without affecting the concentration of anthocyanins, phenolics, and tannins, the results of this study do not indicate a decrease in the rate of grape sugar accumulation as a result of the investigated defoliation techniques. Given the cost of implementing these treatments, the results of this study do not support the use of these methods for the purpose of delaying fruit ripening in a hot Australian climate.
Highlights
The decision of when to harvest is an important consideration in the winemaking process and is based on a multitude of factors including sugar and acidity levels, phenolic maturity, and aromatic and flavour ripeness [1]
The impact of the different defoliation methods on canopy architecture was quantified using the plant area index (PAI) and canopy porosity (Φ), where the PAI describes the total one-sided area of leaf tissue per unit ground surface area [25] and Φ refers to the light penetration through the canopy [24]
This is contrary to the results of Zhang et al [15], who in their study on Shiraz observed a significant reduction in the PAI and increase in Φ on vines which were basally defoliated but not those which were apically defoliated
Summary
The decision of when to harvest is an important consideration in the winemaking process and is based on a multitude of factors including sugar and acidity levels, phenolic maturity, and aromatic and flavour ripeness [1]. Harvest dates are advancing and becoming more compressed, meaning grapes are often picked at higher temperatures when compared to historic dates for their cultivars, with undesirable chemical profiles due to increased sugar concentration and potential wine alcohol level, low acidity, and undeveloped or unbalanced flavour components [5]. This trend towards overly fast ripening is associated with a decoupling between sugar accumulation and phenolic maturity, and it is becoming increasingly common to observe excessively fast sugar accumulation while anthocyanin and tannin development are lagging behind [6,7]. This strategy is simple and suitable to mechanisation, if the foliage being removed is spatially separated from the bunches [16]
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