Hi Mitch,
I have read quite a bit of what Paul White has written on the issue and he was very instrumental in pointing me in the direction of the research that has been done by the Australian Wine Research Institute and others on issues of reduction and oxidation. I conducted an interview with Dr. White in one of the recent issues of my newsletter, which made for some pretty fascinating reading, and I would be happy to share it with anyone who might be interested in his research (just email me at jbgilman@ix.netcom.com). He has taken a lot of heat in some circles for his willingness to tackle this issue by questioning research and cross checking it with other scientists and the accepted literature in the field of chemistry, and from what I have seen, he has been spot on with all of his critiques.
So I am very aware of the standard operating procedure of adding copper sulphate to wines pre-bottling that has been in affect for several years now in Australia and New Zealand for wines that are destined to be bottled under screwcap. I am uncertain of how these now routine additions of copper sulphate to a wine affect their safety for human consumption (as residual copper is left behind in the wine), as there are no longer any regulations in Australia and New Zealand with respect to setting maximum levels of residual copper, given that the Australian Food Standards Code was changed a few years back abolishing any such maximum level for wine. Previously, the regulations in Australia and New Zealand (both countries operate under the same set of rules for wine) had prohibited residual copper concentrations in excess of 5.0 mg. per liter, which was the same as the maximum level currently allowed in the United States. But within the last few years the governments Down Under have scrapped this maximum level of residual copper in wine- “why” being a very good question to which I have not seen any answer.
The questionable aspect here to my mind is that residual copper cannot be tasted or noticed in a wine unless the level is sufficiently high enough to form a haze by the residual copper’s reaction with proteins that might still be in the wine after filtering. Without the “copper haze” formation, there is no way to tell how much residual copper one is consuming when drinking a wine from Australia or New Zealand that has been copper fined, as testing is no longer done for these wines with the abolition of the maximum level for safe human consumption by the good folks responsible for the Australian Food Standards Code. And thanks to GATT, wines produced in one country under regulations that make them safe for their domestic markets are not subject to regulations in the countries that import them, so our FDA maximum limits of 5 mg. per liter of residual copper are not applicable in regards to copper-fined wines from Australasia and are of no use in protecting consumers, just in case there happens to be wines on the market here that are above what is currently deemed safe for human consumption.
In affect, the changes of the Australian Food Standards Code for maximum levels of copper in wine effectively usurped the FDA’s ability to police the US market for wines with potentially hazardous levles of residual copper from Australia and New Zealand, assuming of course that the FDA had any interest in doing so. I had contacted a very nice gentleman at the FDA to ask him about this issue, and he was going to look into it and get right back to me. That was six months ago and I have still not heard from him. But to give one some idea of how potentially wide spread the issue is in Australasia today, the Australian Wine Institute published a paper in April of 2008 written by oenologist Geoff Cowey about the issue, entitled “Excessive copper fining of wines sealed under screwcaps- identifying and treating reductive winemaking characters,” which was published in The Australian & New Zealand Grapegrower and Winemaker. It makes for some pretty interesting reading, to say the least. I highly recommend reading the paper before opening up the next bottle of Australian or New Zealand wine sealed under screwcap.
The bottom line is that today one does not have to be wary of only of residual copper above safe levels for human consupmption, as in addition, one of the methods now often used to try and remove excess copper prior to bottling is what is called a “Blue Fining”, where the wine is fined with potassium ferrocyanide. To quote Mr. Cowey: "However, in most cases (of greater than desired concentrations of copper in the wine), fining with potassium ferrocyanide (PFC), an operation referred to as “blue fining”, is required to decrease the concentraton of copper to below the recommended “safe level”. (I should note that Mr. Cowey’s recommended “safe level” is the 5 mg. per liter that was formally the limit of the Australian Food Standards Code.) The goal of the paper is to give winemakers a firm blueprint for treating wines for potential reduction prior to bottling, so as to minimize the likelihood of excess copper in the wines and the need for blue fining, as Mr. Cowey continues, “over-fining and the retention of excess ferrocyanide in the wine” is not desirable, for “excess ferrocyanide, might, in time, liberate cyanide, thus rendering the wine unsaleable and possibly toxic.” Yum.
The bizarre thing is that all of this is done to allow wines sealed under screwcaps to prolong the period of fine drinking before they become liable to permanent reduction- all of the literature that I have read indicates that all of this addition of copper sulphate prior to bottling only pushes further out the onset of reduction in a wine sealed under an anaerobic seal such as screwcaps currently provide- it most emphatically does not prevent it. So the addition of all this heavy metal is to simply give a wider window for the wine to be consumed prior to the onset of reduction- if the wine is sealed under a screwcap. If the wine is sealed under a cork, then none of this- copper sulphate additions, fining with ferrocyanide- are necessary. Additionally, copper fining does not only target the sulfur molecules that are prone to reduction and the formation of thiols in an anaerobic environment, it targets all sulfur compounds in the wine- many of which are resonsible for the aromatic and flavor complexity that makes wine such a compelling beverage in the first place. The literature that I have seen on this issue is very persuasive. So in the end we add all this copper (or strip it out at the risk of adding cyanide), so that we can make the wine less complex from the start, and only push back the day of reckoning with permanent reduction, all so that we can use a specific type of closure! The whole thing is asinine in my opinion.
I should note that the screwcap industry is feverishly working to create better seals that allow a certain degree of oxygen ingress (trying to emulate natural cork’s performance in this respect), so that in the future all of this copper fining may no longer be necessary. I would be very curious to hear what winemakers here in the US or Europe are doing to address the potential impact of permanent reduction in wines sealed under screwcaps, as of course they are subject to the limitations on residual copper in wines as set out by the appropriate regulatory agencies in their home countries. But in the interim, I am a bit hesitant to not spit out that screwcapped wine from Australasia from the current vintage that I might be sampling, and needless to say, there are none of those potentially heavy metal wines in my cellar. I would love to see some research done on the safe levels of residual copper in wine for those of us that taste and spit the wines
Best,
John