Aim of the study

In this project researchers wanted to determine what the effects of a single heat event, as well as cumulative effects of a number of heat events are on Shiraz berry composition and tannins.


Project layout

In order to control the environment, the experiment was done in a greenhouse on potted Shiraz vines. To simulate a heat event, temperatures were increased by 6°C while fruit and canopy light exposure remained unchanged. The following treatments were applied:

  • Control (C)
  • Heat event at the end of fruit set (HE1)
  • Heat event prior to veraison (HE2)
  • Heat events at both end of fruit set and veraison (HE1&2)

Temperature inside the greenhouse was affected by outdoor temperatures. During HE1, maximum temperatures inside the greenhouse reached 45°C while reaching 40°C at HE2. Berries were regularly sampled from fruit set to maturity, where primary and secondary metabolites as well as tannins were analysed.



  • Photosynthesis was significantly decreased for the heated vines during HE1 where maximum temperature reached 45°C, affecting both berry weight and titratable acidity.
  • Shiraz showed an elastic response to HE1. Skin tannin was mostly affected short after the heat event, along with seed tannin, but by maturity these differences were no longer evident.
  • HE2 had no effect on photosynthesis and less direct impact on berry composition, metabolites or tannins.
  • Some primary metabolites were affected by either HE1 or HE2 such as valine, leucine, pyruvic and lactic acids.
  • Two heat events (HE1&2) showed increased malic acid by harvest and delayed the onset of veraison. However the phenolic profile and sugar at harvest were similar to controls.


Significance of the study

The reality of climate change means that more frequent, extreme events such as heatwaves can occur. This research indicated that well-irrigated Shiraz grapevines showed that they could adapt to a short-term heat stress of 45°C during berry development and remain unaffected at a temperature just above 40°C.



Gouot, J. C., Smith, J., Holzapfel, B., & Barril, C. (2019). Single and cumulative effects of whole-vine heat events on Shiraz berry composition. OENO One53(2).

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