There are many factors that play a role on the quality and stability of wine. Specifically, both enzymatic and non-enzymatic oxidative reactions can significantly influence the aromatic and structural quality of a wine, which without appropriate control, can run rampant and cause off-aromas and flavors in the wine, thus spoiling the beverage. Spoilage microorganisms (such as certain yeasts and bacteria), as well as compounds naturally present in wine can cause oxidation reactions or become oxidized themselves, resulting in undesirable sensory characteristics in the finished wine.
In order to control these spoilage microorganisms and undesirable chemical reactions, winemakers employ SO2 (sulfur dioxide) during the winemaking process. Recently there has been a strong push for winemakers to reduce their usage of SO2, mainly due to the fact that SO2 exposure could be a health risk for certain individuals. Currently, there isn’t one compound or product that can completely replace SO2 in winemaking, though research is ongoing and has already found that reducing the amount of SO2 used in conjunction with another alternative technology could protect the finished wine just as well as higher levels of SO2 used alone. These alternative technologies include hydrostatic pressure, pulsed electric fields, ultrasound irradiation, and UV (ultraviolet) irradiation.
The study presented here proposes to examine the use of UV irradiation as a protective agent against wine spoilage, while comparing with SO2 and no treatment controls. The measure for determining if any of the treatments protected against wine spoilage or oxidation was polyphenol oxidase activity. Polyphenol oxidase is partially responsible for the browning of white wines after oxidation, so theoretically, if polyphenol oxidase levels are decreased, the wine is not oxidized (or is less oxidized) than a wine with higher polyphenol oxidase levels.
Two white grapes were used in this study: Xarel-lo and Parellada (from vineyards in Spain). Grapes were processed in a home juicer and then pressed. To remove any solids, juice samples were centrifuged then the liquid removed. The juice was then split, with half remaining as fresh juice and the other half going into a freezer. For both fresh and frozen juice, samples were split into the following treatments: 1) SO2 addition (50 mg/L potassium metabisulphite) prior to winemaking; 2) UV irradiation treatment prior to winemaking; and 3) winemaking without SO2 or UV treatments (control).