Too much of a good thing: Excess grape potassium impacts wine quality

 

Author: Annie Klodd, UMN Extension Educator - Fruit Production. kloddann@umn.edu

Reviewed by Drew Horton, UMN Grape Breeding and Enology Program

 

It is well known that grapes containing excess potassium can cause problems for wine making. This is especially true in red wines - grape skins are sinks for potassium, and red wines are fermented with their skins.

Basically, excessive potassium (K+) in the grape juice or must negatively impacts wine quality by increasing the pH of the must past suitable levels. This occurs because excess K causes precipitation of tartaric acid and other free acids. As that happens, the pH goes up. Ramifications can include reduced respiration in wine, color instability, microbial instability (spoilage), and premature oxidation.

Several research studies have found that juice pH is highly correlated to K+ levels. However, even if the grapes are harvested at recommended pH levels, excessive K+ content in the fruit can cause the grape must pH to rise dramatically in the first few days of fermentation (Walker et al. 2008).

 

Grape growers can do a number of things to keep grape potassium levels in check.

Moderate shading with good canopy management: Past studies found that potassium is higher in more shaded clusters. The reason for this is not well understood. Prevent excess shading by balancing the canopy with pruning, shoot thinning, leaf thinning, and avoiding excess N fertilization.

Follow soil and foliar nutrient test results: Take soil tests every 3-5 years, and foliar tissue tests every year during bloom or veraison. Stop applying K if the soil test indicates "high" or "excessive." Soil K concentration over 101 ppm is considered high based on research in Minnesota.

Harvest based on recommended pH levels: K increases linearly with berry pH. Unless you are saving the grapes for ice wine, harvest within suggested pH ranges.

For more information on this topic, please join us for a webinar on Acidity Management on Tuesday, May 31 at 3:00pm, co-hosted by University of Minnesota and Iowa State University. REGISTER HERE.

 

Sources: 

Rosen, C. and R. Eliason. Nutrient Management Guide for Commercial Fruit and Vegetable Crops in Minnesota. 2005. University of Minnesota Extension.

Christensen, P. Foliar Fertilization of Grapevines. University of California Kearney Agricultural Center. Date unknown.

Walker et al. 2008. The effects of the rootstock Ramsey on ion and organic composition of grapes and wine, and on wine spectral characteristics. Australian Journal of Grape and Wine Research.

https://doi.org/10.1111/j.1755-0238.1998.tb00138.x

https://extension.psu.edu/assessing-and-managing-potassium-concentration-in-the-vineyard

https://psuwineandgrapes.wordpress.com/2016/09/23/making-red-wine-from-fruit-high-in-potassium/#:~:text=High%20potassium%20concentrations%20can%20cause,wines%20can%20be%20negatively%20affected

https://winesvinesanalytics.com/features/article/176319/Potassium-Accumulation-by-Grapevines