In various countries the addition of water to grape must pre-fermentation is permitted in order to lower the risk for stuck fermentations. It has also been proposed in South Africa as a warm viticultural climate and is currently under consideration. There are basically two ways in which water can be added to grape must: by running off juice and substituting it with water, or by direct addition of water that will increase the final wine volume. The aim of this Australian study was to compare the two ways of water addition to lower initial grape sugar, to harvesting earlier at that sugar. Studies were previously performed on Cabernet Sauvignon and Merlot with very promising results and the decision was taken to evaluate the effect of water addition on Shiraz, Australia’s main red cultivar.

 

Project layout

Shiraz grapes were hand harvested from a Nuriootpa research vineyard in South Australia.

There were three harvest dates at three different sugar levels (H1-3).

The sugar levels were: 24.3°Brix (H1), 26.3 °Brix (H2) and 28°Brix (H3).

Small scale fermentations were conducted with EC 1118.

Chlorine free water (rain water) was used to adjust the sugar levels of the H3 juice to similar levels as the H1 and H2 juice.

Water was acidified with tartaric acid and either just added to the high sugar juice or added after some juice has been drawn off (substitution).

Basic wine analysis and phenolic compound analysis were done in finished wines.

 

Results

Phenolic compounds, especially anthocyanin and tannin concentrations, increased with the ripening levels of the grapes.

Water addition to the H3 juice in any form decreased phenolic composition in the final wines when compared to the H3 control wine without any water addition.

There was no difference in the phenolic concentrations between the two types of water additions, meaning one can just add water and don’t need to substitute.

The wines made from water added musts (both types) had higher concentrations of phenolic compounds than the wines made from grapes harvested earlier at the same sugar concentration of the water added musts.

 

Significance of the study

This study has indicated that adding water to Shiraz grape musts before fermentation is a potentially viable strategy to lower alcohol concentrations in final wines. Even though the phenolic content will be lower than the undiluted wines, the concentrations of anthocyanins and tannins will still be higher than wines made from grapes harvested earlier. The limitation of the study is though that no sensory analyses were performed, which is a very important aspect to consider in terms of final wine quality and consumer acceptance. Once legal in South Africa, winemakers are encouraged to trial this practice first before attempting it on a larger scale.

 

Reference

Teng, B., Petrie, P., Smith, P. and Bindon, K. (2020). Comparison of water addition and early‐harvest strategies to decrease alcohol concentration in Vitis vinifera cv. Shiraz wine: impact on wine phenolics, tannin composition and colour properties. Australian Journal of Grape and Wine Research, 26: 158-171. doi:10.1111/ajgw.12430