AS DVO 08
Grapevine cation and anion transfer: A perspective from the soil to wine chemical and sensory properties.
Strever, A E
Stellenbosch University. Department of Viticulture and Oenology
Strever, A E
Objectives & Rationale
Wines with high cation and anion concentrations (sodium, chloride and sulphates) can be found in many wine grape-growing regions across the world, and have also been identified in some South African wines. These wines were made from grapes grown on soils with high levels of soils salinity and sodicity. Questions arose concerning the primary origin of the salinity/sodicity, the cation and anion concentrations occurring in the grapevine itself, the cation and anion content of the grape juice and wine, the different cation and anion measurement techniques locally and overseas, as well as the practices implemented for the management of salinity/sodicity. In addition to this, anecdotal evidence exists that some wines with higher mineral contents may also have positive style attributes.
Vineyard blocks of Chenin blanc and Pinotage in the Paardeberg area were divided into “high salinity” and “low salinity” based on aerial imaging. Soil analysis were conducted at three depths as well as vegetative analysis (shoot measurements, leaf blades, petiole and shoot sampling, trunk circumference, destructive leaf area and pruning mass). Mesoclimate loggers were installed and berry sampling conducted as well as harvest measurements. Standard winemaking practices were followed and cation and anion analysis were conducted at different laboratories (juice, skins, homogenised, sediment and wine). Winescan, colour and phenolic analyses as well as descriptive sensory analysis have been performed.
Soil samples confirmed the presence of salinity/sodicity in the plots, which affected the growth as well as yield per vine. Shoot, petiole and leaf analysis showed high levels of sodium, reaching values greater than 1500 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 differences were reported between analyses of the different laboratories. The sensory analysis showed that wines that had high cation and anion content were described as oily, and in 2015 these wines also were described as having “harsh ‘grippy’ tannins”.
The saline/sodic conditions of some of the sites where grapes were used to make wine affected the grapevines’ performance. The different cation and anion concentrations in the shoots, petioles and leaf blades showed that some cations and anions were definitely transferred into the grapevine from the soil. The subsequent juice extracted from the grapes also showed high levels of certain cations, however the juice sediment analysis showed the highest concentrations of cations compared to the skins, the homogenised and juice sample. This could then consequently affect wines that undergo skin/lees contact for long periods of time. The wines made from the high cation content juice had lower levels of cations and anions, which could be due to various reasons that would still need to be investigated. The 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 cation and anions.