Manipulating winegrapes with antitranspirants

Abstract

Increasing temperatures are impacting grape production, winery logistics and affecting resultant wines. To address this we tested the efficacy of a film-forming antitranspirant, di-1-p-menthene, to manipulate winegrape ripening. Berry weight, bunch weight and yield were increased in treated vines, but anthocyanin concentration was reduced. Pinot Noir and Shiraz wines made from treated vines were lower in alcohol concentration, providing an alternative to water addition at the winery and in keeping with a growing consumer trend for lower alcohol products. Pivot profiling results highlighted perceived attribute differences, suggesting this treatment might provide vignerons an easily adoptable mitigation tool to address vintage compression and other climate change effects.

Summary

To determine if winegrape production could be manipulated without negatively affecting specific grape and wine parameters, this project tested the efficacy of an antitranspirant on two red Vitis vinifera L. cultivars, Shiraz and Pinot Noir.

Nine field trial sites were established on commercial vineyards across seven wine growing regions of NSW. The antitranspirant di-1-p menthene was applied at a 1% application rate as a single treatment at pre-flowering, pre-veraison, or both, to form a flexible film surface coating. The coating forms a physical barrier which reduces water loss from the leaves, bunches and other vine parts, whilst allowing them to breathe normally. These were compared against an untreated control.

The trial was undertaken in one season during drought-declared conditions of 2017-2018 in NSW, providing an excellent opportunity to trial the effectiveness of the antitranspirant. Berry weight, bunch weight, and yield were all increased across the majority of sites, while pH and titratable acidity (TA) remained mostly unaffected by application of the antitranspirant. Reductions in °Brix and anthocyanins occurred across several sites, with no impact on total phenolics across any site.

Juice samples were taken from the sites in which wines were made. No differences in pH or Baumé occurred. However, TA was increased in juice from all treatments except the dual antitranspirant treatment for Pinot Noir. Shiraz YAN was not affected by the antitranspirant while Pinot Noir YAN was decreased in all treatments.

Alcohol concentration was decreased in both Pinot Noir and Shiraz wines from treated vines. Total red pigments in the Shiraz were significantly reduced in all antitranspirant treatments. Acetic acid concentrations were increased by the treatment, with TA decreased in Pinot Noir wine and pH increased in Shiraz wine with treatment. However, no significant differences resulted between treatments in free, bound or total sulphur and phenolics in both wines.

Pivot profiling was able to separate the Pinot Noir trial wines in a more distinct and logical manner than Shiraz trial wines. Perceived attributes of antitranspirant wines were expressed as less ripe, green, herbaceous and high acidity whereas control wines were characterised as more red (less orange/brown), darker and associated with higher alcohol and complexity.

This project achieved its aim of evaluating use of the film-forming antitranspirant di-1-p menthene on two red grape varieties across different viticultural climatic zones of NSW. These preliminary results suggest this treatment might provide vignerons with an easily adoptable mitigation tool to address vintage compression and changes to grape, juice and wine characters caused by climate change. However, further long-term research across several seasons is required to assess the full potential and benefit of its use.