WINETECH Technical Yearbook 2020

With a pinch of salt…

OBJECTIVES AND RATIONALE The main questions were related to the primary origin of the salinity/sodicity, cation and anion concentrations occurring in the grapevine, 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 suggested that some wines with higher mineral contents may also have positive style attributes. The potential sensory impact of salts in wine therefore had to be considered. TABLE 1. Tank samples of some wines exhibiting high sodium and chloride levels (mg/L). Cl Na 13/701 49.6 43.54 13/702 53.2 39.35 13/703 46.1 50.03 13/704 58.5 86.00 13/705 90.4 152.81 13/706 129 227.54 13/707 42.5 58.05 13/708 489 324.24 13/709 128 142.39 13/710 347 262.83

through persistent droughts. Cation and anion analysis in the leaves, petioles and grape components is essential for the prevention of the negative effects it may have on grapevine physiology, the grape juice and also the wines made from it. The OIV resolution (Oeno 6/91) with regard to sodium states that: “When wine contains excess sodium (excess sodium is equal to the content of sodium ions less the content of chloride ions expressed as sodium), it is generally less than 60 mg/L, a limit which may be exceeded in exceptional cases…”. As a result of these restrictions, some wines may even be rejected from the export market. High concentrations NaCl also have an effect on the sensorial quality of wine, and may as a result be described as flat, dull, soap, seawater-like and saline. Some local wine tank samples were found to exceed the stated OIV limit, as well as the local beverage limit, of 100 mg/L significantly in some cases (see table 1). Australia already in 1997 published an article (Leske et al. , 1997) to create awareness of sodium levels in Australian wines. In Australia, for example, the sodium content may not exceed 1 000 mg/L in wine, as the country has a high occurrence of saline and sodic soils. It seems that some regulators do not even consider chloride levels as recommended in the OIV legislation, which makes a huge difference in interpretation.

APRIL 2020

ALBERT STREVER: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch KEYWORDS: Salt, cations, anions, wine, grapevines

and 10. Grapevines should grow normally at values below 2.5 dS/m, resistance over 300 Ohm, and at soil pH levels between 5 and 7.5. Grapevines are known to be moderately sensitive to salinity, but salinity and sodicity can have an adverse effect on plant growth, whether directly or indirectly. These conditions also affect the grapevine’s physiological responses, causing yield reduction, decrease in shoot growth and increase in cation and anion concentrations in the fruit and final wine. It may also affect the biochemical pathways, leading to toxicities, deficiencies and mineral imbalances in the plant. The most important cations associated with salinity are Na + , Ca 2+ and Mg 2+ , whereas the most important anions are Cl - , SO 4 2- and HCO 3 . They may occur naturally in the soil, but more commonly are added to the soil through irrigation, also exacerbated

Although salinity or sodicity may be localised to certain production areas, the study aimed to provide insight into the potential impact of cations and anions in wine and its origins, from a positive, as well as potentially negative perspective. INTRODUCTION Soil salinity and sodicity occurs mostly in arid and semi-arid environments. Saline soils have high concentrations of soluble salts (e.g. NaCl) in the soil solum/regolith with electrical conductivity values of over 4 dS/m and resistance of less than 300 Ohm, an exchangeable sodium percentage of lower than 15 and pH lower than 8,5. Sodic soils in turn have a high concentration of sodium ions compared to other cations, with electrical conductivity values of lower than 4 dS/m, sodium adsorption ratio of over 13, an exchangeable sodium percentage of over 15 and pH between 8,5

WINETECH TECHNICAL YEARBOOK 2020 10