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Copper

An essential micronutrient, it can also affect wine oxidation. Joshua Godshaw, 2016

Copper is an essential micronutrient present in wine usually as a result of the grape growing environment and can be toxic to humans at extreme concentrations. American soil copper concentrations are typically ~26 mg/kg, measured as total copper, but can increase substantially due the use of copper containing vine treatments including Bordeaux mixture (ATSDR 2004). High total copper concentrations prior to fermentation can inhibit yeast growth and retard fermentation.  Typical copper concentrations in finished wine worldwide rarely exceed 3 mg/L, with residual copper concentrations limited to 0.5 mg/L in finished American wine (C.F.R 27: §24.246). White wines treated with copper (II) sulfate to remove aromatic sulfides, such as hydrogen sulfide, are typically higher in copper content as a result of inefficient copper removal strategies post-addition and is limited to additions of 6 mg/L in the United States (C.F.R 27: §24.246).

Like most metals, copper is frequently associated with wine oxidation processes. It has been shown that copper contributes to accelerated rates of SO2 consumption when in the presence of iron and a polyphenol, although an exact mechanism has not been proven. In terms of quality, copper is often targeted as the culprit of metal haze formation in wine, producing a darkened red-brown hue in white wines from the formation of complexes with large molecules such as tannin. Copper species can be separated analytically based on their physical-chemical properties as its cationic (Cu2+), residual, and organically bound forms. However, successful identification of organic copper species in wine has yet to be accomplished.

SOURCES:

(ATSDR), Agency for Toxic Substances and Disease Registry. 2004. “Toxicological Profile for Copper.” Department of Health and Human Services, Public Health Service, no. September.

Alcohol and Tobacco Tax and Trade Bureau, Treasury. Materials Authorized for Treatment of Wine and Juice. 2016. Title 27 C.F.R.  §24.246

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