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60 WINES&VINES July 2017 WINEMAKING WINE EAST P rocessing wine from high-pH fruit can create potential diffi- culties for winemakers. Not only can stability issues such as color, sulfur-dioxide management and microbial content be problem- atic, but high-pH wines resulting from high potassium (K or K + ) concentrations add ad- ditional challenges for winemakers. Making wine with high-potassium fruit is not isolated to the eastern United States, and studies pertaining to the topic have been pub- lished globally. Concentrations of 22-32 mmol/L K + (~860-1,279 mg/L K + ) are consid- ered "normal" ranges for wine grapes (Somers 1977), whereas ranges in the 27-71 mmol/L K + (~1,056-2,776 mg/L K + ) are considered "high" (Somers 1975). These higher ranges of potassium in the fruit tend to lead to potential winemaking problems throughout the duration of wine manufacturing. Such difficulties include: • Large increases in pH during primary and malolactic fermentations, which drive the finished wine into a high pH (sometimes >4.20) range; • Color hue, intensity and stability of red wines can be negatively affected; • Longevity of wines may be decreased; • Potential negative perceptions associ- ated with taste and mouthfeel for both white and red wines; • Wine stability problems such as micro- bial stability (both in terms of micro- flora and inhibition of growth), sulfur dioxide levels and efficacy, color stabil- ity of red and rosé wines, stability of tartaric acid and protein stability; • An increase in oxidative potential, which may cause premature oxidation for young wines. Potassium and grapevines High potassium problems recently have been addressed by many in the regional viticulture community. Dr. Tony Wolf, professor of viticul- ture and director of the Alson H. Smith Agri- cultural Research and Extension Center at Virginia Tech, published a change in potassium fertilization recommendations for vineyards in the July 2016 volume of Viticulture Notes, where he recommended reducing the 75 ppm (150 pounds per acre) rate found in the 2008 Wine Grape Production Guide for Eastern North America to 40 ppm (80 pounds per acre). In September 2016, Dr. Michela Centinari offered solutions for reducing potassium up- take by the vines: • When establishing a vineyard on a site with a high exchangeable potassium level, it can be useful to select root- stocks with lower potassium uptake ca- pacity. The most common rootstocks Coping with High-pH Wines Addressing high-potassium concentrations in the fruit during winemaking operations By Denise M. Gardner KEY POINTS High-pH wines are a common problem in wine- making regions worldwide. The first step toward resolving high-pH winemaking challenges is to check potassium levels in the vineyard—both in the soil and the grapevines. In the winery, acid adjustments to the must may be a practical method of addressing wine-qual- ity issues resulting from high-potassium fruit, especially when techniques such as ion ex- change are too expensive or not available for small wineries. Researchers at Pennsylvania State University conducted production trials on the musts of two red wine varieties to determine the impact of higher than normal tartaric acid additions pre-fermentation to potentially decrease potas- sium concentrations. DENISE M. GARDNER