Late pruning and warmer temperatures – effect on Shiraz wine

by | Jul 30, 2021 | Winetech Scan

Many growers delay pruning in an attempt to delay ripening to mitigate harvest compression associated with a warming climate. Elevated temperatures can affect berry composition and wine sensory characteristics. In this project, researchers evaluated the interaction between delayed pruning and rising temperatures on the chemical and sensory characteristics of Shiraz.

Project layout

  • The trial was done over two years in the Barossa Valley on Shiraz;
  • Vines were spur pruned and trained onto a single cordon with sprawling canopies;
  • A factorial combination of three pruning times and two thermal treatments were established;
  • Pruning treatments included a winter pruning control and two late pruning treatments – one at 50% budburst and the other when 2-3 leaves emerged on 50% of spurs;
  • The two thermal regimes were ambient temperature and a heated regime. Daily mean temperature of the canopy in the heated treatment was increased with 0.4°C in relation to ambient temperature in the first year of the trial, and increased with 0.68°C in the second year;
  • Yield and bunch numbers were recorded and berry parameters measured;
  • Wine was made from each combination and chemically and sensorially analysed.

Results

  • Later pruning delayed phenology with neutral or positive effects on yield and berry parameters compared to controls. Where vines were heated, the delay in phenology was shorter compared to unheated vines;
  • In the first year, heated vines had 60% higher yield compared to unheated vines due to bunch number increasing;
  • In the second year, later pruning at budbreak increased bunch number and yield;
  • Effects of temperature and timing of pruning on wines were season dependant;
  • Where vines were heated, a reduction in wine colour was observed. The wine also had more floral aromas, was lighter bodied with less tannins and did not have palette length, compared to wines made from ambient temperature vines;
  • Anthocyanins, colour density and phenolic substances correlated negatively with mean temperatures during the two weeks after veraison – highlighting the importance of this particular period during ripening;
  • Interactions between pruning and temperature treatments showed that delaying pruning until 2-3 leaves have emerged could mitigate the effects of a warmer climate by increasing wine colour and fruit intensity in the two seasons of the trial.

 Significance of the study

As climate changes and temperatures increase, the sensory attributes of wines are affected while cellars experience pressure due to harvest compression and loss of wine quality when grapes are harvested too late. Finding viticultural practices to mitigate these challenges, are essential to adapting to climate change. Delayed pruning is one tool that can be used to relieve harvest compression and somewhat counteract the detrimental effects of warmer temperatures, without having negative effects on vine phenology, yield or wine characteristics.

Keep in mind that delaying phenology with delayed pruning has limitations in other pruning systems such as cane or mechanical pruning due to apical dominance.

Reference:

Moran M.A., Bastian S.E., Petrie P.R., and Sadras V.O. Impact of late pruning and elevated ambient temperatures on Shiraz wine chemical and sensory attributes. Australian Journal of Grape and Wine Research 27, p 42-51, 2021. https://onlinelibrary.wiley.com/doi/epdf/10.1111/ajgw.12470

Image source: Pixabay

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