Stephan Sommer,* Jannik Janz, and Dominik Suess
*Appalachian State University, 730 Rivers Street, Boone, NC 28608 (sommers@appstate.edu)

Iron and copper act as oxidation catalysts and can lead to browning reactions and other detrimental oxidative changes in wine. These compounds are introduced throughout the process from fungicides, fining agents like bentonite, and vineyard soil and winemaking material. Removal of heavy metals prior to bottling is critical to ensure prolonged shelf life and prevent accelerated aging. This goal can be achieved with the addition of phytic acid, potassium hexacyanoferrate(II) (PHCF), and a PVPP based synthetic polymer, Divergan HM. PHCF cannot legally be used in the United States and phytic acid only removes iron, so Divergan HM is currently the only approved method to remove copper from wine. In contrast to other fining methods, there is no inexpensive quick test for iron and copper before and after the application. The objective of this study was to implement a colorimetric quick test to control the removal efficiency of heavy metal fining agents in wine. The tests are based on complexation reactions of iron and copper with organic molecules and the comparison of the corresponding color on a scale in a range between 0.1 mg/L and 50 mg/L. Total iron can be analyzed by reducing Fe3+ to Fe2+ in the sample prior to the reaction. For the iron test, brown and red wines should be treated to remove color, while copper can be analyzed in any wine without pretreatment. The tests take about five minutes for iron and ten minutes for copper with a combined cost of $0.65 per sample. The test is a great alternative to lab-based methods, not only because of the low cost, but also because, being a quick test, it is easy to use in a winery environment, even by untrained personnel.

Funding Support: N/A