How to Deal with Uninvited Guests in Wine: Copper and Copper-containing Oxidases

Abstract

Copper is one of the most frequently occurring heavy metals in must and wine. It is introduced by pesticides, brass fittings, and as copper sulphate for treatment of reductive off-flavors. At higher concentrations, copper has harmful effects on the wine. It contributes to the oxidation of wine ingredients, browning reactions, cloudiness, inhibition of microorganisms, and wine fermentation. Last but not least, there is also a danger to the consumer. At present, some physicochemical methods exist to reduce the copper content in must and wine, but they all have their shortcomings. A possible solution is the biosorption of metals by yeasts or lactobacilli. Copper can also reach must and wine in the form of copper-containing phenol oxidases (grape tyrosinase, Botrytis cinerea laccases). Similar to free copper, they oxidize phenolic wine compounds, and thus lead to considerable changes in color and nutritional value, making the product ultimately unsaleable. All measurements for enzyme inactivation such as heat treatment, and addition of sulphites or bentonite are either problematic or not effective enough. The application of oenological tannins could offer a way out but needs further research.

Unravelling the Impact of Grape Washing, SO2, and Multi-Starter Inoculation in Lab-Scale Vinification Trials of Withered Black Grapes

“…S. cerevisiae, which represents a minor population on the surface of heathy grapes [26], was not detected, as also reported by Prakitchaiwattana et al [31]. [32][33][34]. Their concentration in wine, especially copper, is reduced during fermentation, as they are essential trace elements for the growth of S. cerevisiae [34][35][36].…”

“…tices (fertilizers and pesticides), dust residues, contamination with winemaking equipment, or through winemaking additions (fining agents, such as copper sulphate) [32][33][34]. Their concentration in wine, especially copper, is reduced during fermentation, as they are essential trace elements for the growth of S. cerevisiae [34][35][36].…”

Determination of Iron, Copper and Zinc in the Wine by FAAS

“…Approximately the same values in relation to the cupper concentration in the wine have been reported by other colleagues as well. According to a study in which 72 wines were analyzed, the average copper content was 0.18 mg/L with a maximum of 0.55 mg/L [11,17]. Maciel et al (2019) [12] indicates that the concentration of copper in all analyzed wine samples has been below (from 1.0 to 10.3 µg L−1) the maximum acceptable limit set by the OIV (1000 µg L−1).…”

Current research progress on laccase-like nanomaterials

“…21,22 Besides, it can also be used to stabilize wine and beer. 23,24 Laccase is used in the bread industry because it can increase the strength and stability of the dough, reduce the dough stickiness, and improve its processability. 25 Laccase also has great potential in biosensing applications.…”