Resumen de Potassium concentration and pH inter‐relationships in grape juice and wine of Chardonnay and Shiraz from a range of rootstocks in different environments
Rob R. Walker, Deidre H. Blackmore
Background and Aims: pH adjustment during winemaking is a significant cost to the Australian wine industry. This study addresses potassium (K+) concentration and pH inter‐relationships in grape juice and wine of Chardonnay and Shiraz.
Methods and Results: Chardonnay and Shiraz on own roots, and on Ramsey, 1103 Paulsen, 140 Ruggeri, K51‐40, Schwarzmann, 101‐14, Rupestris St. George and 1202 Couderc were compared at Koorlong and Merbein (Victoria), and Padthaway, Nuriootpa and Rowland Flat (South Australia). Petiole K+ concentrations at flowering were a poor indicator of grape juice and wine K+ concentrations. The concentration of H+ ions in grape juice and wine decreased as K+ concentrations increased resulting in increased pH. The relationship between H+ and K+ concentrations was linear for Chardonnay but exponential for Shiraz, where K+ concentrations were higher. Wine K+ and grape juice K+ concentrations exhibited a positive linear relationship, with slope for Chardonnay about half that for Shiraz, indicating a net loss of K+ between grape juice and wine of 58% for Chardonnay and 13% for Shiraz.
Conclusions: The study has linked higher wine pH to both higher juice soluble solids and K+, and to poorer wine colour hue. Loss of K+ during fermentation and cold stabilisation appeared higher for Chardonnay than for Shiraz.
Significance of the Study: Rootstocks that lead to lower K+ concentrations and pH in grape juice and wine are identified. Differences in the K+ concentration dynamics between grape juice and wine of Chardonnay and Shiraz are described and quantified.
