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Less K = less acid = less money

RD&E News | January 2020
10 Jan 2020
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A Wine Australia Incubator Initiative project testing whether potassium uptake can be lowered in Cabernet Sauvignon has added to our understanding of the effect that rootstocks have on wine pH.

The findings are valuable, because lower potassium (K) levels mean less acid needs to be added during the winemaking process – offering welcome cost savings to winemakers.

The study – led by ARC Training Centre for Innovative Wine Production Postdoctoral Fellow, Dr Zeyu Xiao from the National Wine and Grape Industry Centre (NWGIC) at Charles Sturt University – was conducted in a vineyard in the Limestone Coast region in South Australia.

The ultimate goal of this research was to evaluate whether potassium (K) uptake in grapes could be lowered with the use of rootstocks, in order to optimise grape juice pH and titratable acidity (TA), in the vineyard’, Zeyu said.

The research team investigated the rootstock effect on K uptake and grape juice pH , along with concentrations of other elements potentially interacting with K uptake in grapes, including calcium (Ca) and magnesium (Mg).

‘It is known that the performance of rootstocks can vary depending on a number of factors, including, but not limited to, soil type, irrigation strategy, pest pressure and the scion/rootstock combination. Before this research, cation uptake by Cabernet Sauvignon scion on a range of rootstocks including Merbein 5489 (M5489), Merbein 5512 (M5512), Börner, 110 Richter (110R), 1103 Paulsen (1103P), 140 Ruggeri (140R) and Ramsey – growing in the Terra Rossa soil of the Coonawarra region – had not been studied’, said Dr. Suzy Rogiers, Principal Research Scientist from NSW Department of Primary Industries (DPI).

The project’s Final Report says that ‘while no particular rootstock stood out in its ability to limit Cabernet Sauvignon berry K accumulation, Börner berries tended to have slightly lower concentrations (< 10 per cent) relative to vines on their own roots.’

Across all rootstocks tested, juice pH tended to increase, while juice TA tended to decrease with greater juice K concentration.

It was found that juice TA was higher for the rootstocks 140RU and 110R, and juice pH tended to be lower for the rootstocks 110R, 140RU, M5512 and M5489.

There was no effect of rootstock on total soluble solids.

NWGIC Director, Professor Leigh Schmidtke said this study had demonstrated that rootstocks were a potential tool that growers could use to limit K uptake by Cabernet Sauvignon grapes, in order to manage acidity of berry juice, and ultimately of the must and wine.

‘The results generated in this one year study provided us new insights for future studies in comparing the suitability of rootstocks for optimising pH and TA in grape juice in the vineyard.’

Dr Kerry DeGaris, from the Limestone Coast Grape and Wine Council, said this Incubator Initiative project would complement a winemaking and sensory study currently being undertaken as part of a broader trial, and contribute to a better understanding of the impact of rootstocks on Cabernet Sauvignon wine quality and sensory characteristics.

‘Multiple vintages in the same region could also be helpful to further assess the effectiveness of using rootstocks as a tool to modify K uptake in grapevines under different growing seasonal influences’, Zeyu said.

The NWGIC is an alliance between Charles Sturt University, the NSW Department of Primary Industries (DPI) and the NSW Wine Industry Association.

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This content is restricted to wine exporters and levy-payers. Some reports are available for purchase to non-levy payers/exporters.