WINETECH Technical Yearbook 2020

MATERIALS AND METHODS Areas with soil salinity and sodicity were selected in Chenin blanc and Pinotage vineyards from two farms in an arid area of the Western Cape with hot and dry summers. The plots, of which one was rain- fed and one irrigated, were divided into ‘high’ and ‘low vigour’ according to salinity and sodicity levels and aerial imagery. Soil analysis was conducted at three depths to confirm the presence of high cation and anion concentrations. Meso-climate loggers were installed on both farms in order to analyse the climatic effects on the grapevine. Vegetative and reproductive measurements were conducted including trunk circumference measurements, shoot measurements, destructive leaf area measurements, berry sampling and harvest measurements. The cation and anion concentrations in the soil, different grapevine parts (leaves, petioles and canes), grape berry parts (juice, homogenised grapes, skins and the sediment after juice settling), and in the subsequent wines were also assessed and the sensory profile of the wines were determined. RESULTS AND DISCUSSION Soil samples confirmed the presence of salinity/sodicity in the plots, which affected the growth (as measured through shoot

juice sediment, stressing the importance of judicious skin contact. Wines made from high cation content juice did not always show high levels of cations and anions, warranting further investigation. Sensory analysis showed that at certain concentrations sensory factors could be affected positively or negatively by high salt content in wine. Analysis methods differed between laboratories, and there is a need for standardisation of methods and calibration between the labs. REFERENCES Leske, P.A., Sas, A.N., Coulter, A.D., Stockley, C.S. & Lee, T.H., 1997. The composition of Australian grape juice: Chloride, sodium and sulphate ions. Australian Journal of Grape and Wine Research 3, 26-30. Muller, K., 2017. Grapevine cation and anion transfer: A perspective from the soil to wine chemical and sensory properties. MSc(Agric) Thesis, Stellenbosch University, March 2017.

levels of cations and anions, which needs further investigation. Sensory analysis has indicated that, at certain concentrations, sensory factors could be affected positively or negatively, however, this was dependent on the concentrations of the cations and anions. Considering that we found different interpretations in accepted limits, as well as considerable differences in analysis results between laboratories on the same samples, we recommend clear guidelines to be set for accepted limits, as well as analysis methods. SUMMARY Wines wi th high cat ion and anion concentrations can be found in many wine grape-growing regions across the world, and this have also been reported for some South African wines, originating from grapes grown on soils with high levels of salinity or sodicity. Questions arose concerning the origin of the salinity/ sodicity, cation and anion concentrations occurring in the grapevine, as well as the grape juice and wine, different measu­ rement techniques, as well as the practices implemented for the management of salt content in wines. The sensory impact was also investigated. The study confirmed ion transfer from soil to vine to grape and into the wine, and showed high concentrations of certain cations in the

growth, trunk circumference and leaf area), as well as yield per vine. Shoot, petiole and leaf analysis showed high levels of sodium, reaching values greater than 1 500 mg/L. The juice cation and anion analysis showed high levels of sodium for some plots, however, chloride levels were found to be below harmful limits. There were differences between juice, sediment, skin and homogenised sample analysis, confirming that the sediment contained the highest cation and anion content. Some marked differences were reported between analyses of the different laboratories. Descriptive sensory analysis showed no significant differences in terms of saltiness, however, some wines exhibited significant differences between aroma and taste descriptors. The high salt content in the wine may also have had a positive effect on the taste of the wine. At low salt concentrations wines may appear to be sweeter, or less bitter. CONCLUSIONS The study confirmed ion transfer from soil to vine to grape and into the wine, and also showed how high concentrations of certain cations can exist in the juice sediment. This could affect wines that undergo skin/lees contact for long periods of time. The wines made from the high cation content juice surprisingly had lower

For more details on this project, please refer to Muller (2017) and for more information, contact Albert Strever at aestr@sun.ac.za.

WINETECH TECHNICAL YEARBOOK 2020 11