I reproduce here an edited version of a post about the pox I made on Wine Pages.
I have often stated my opinion but will do so again. Its disputed by some but having tasted literally hundreds of white Burgundies, asked to by our Committee, I consider that cork is a major element in the pox. White Burgundy is also more fragile as global warming is producing riper wines with less acidity and this is part of the problem too. My synthesis is pox occurs when a wine with low sulphur is bottled with a poor batch of corks which are porous to air.
I have noted POX in white Rhônes and Alsace wines and some red wines. But generally wines like Alsace riesling do not undergo malo so have more acidity, gewurztraminer is protected by its phenolic compounds, sweet wines are protected by their sugar, reds are generally protected by their tannins, so these wines are much less likely to oxidise. It occurs with many “natural” wines. White Burgundy is a wine of relatively modest acidity which is kept in large numbers and for longer than many other whites which is why it is most affected.
There were many occasions when a consumer said a wine was poxed and we tasted a bottle and found quite often it wasn’t, so I decided when a customer complained to open 6 bottles. My boss refused this for a long time but eventually gave in. Also when I did a tasting from our stock, as requested by the TWS Committee, I tasted 6 bottles of the same wine too. Tasting 6 bottles one can have all good, all poxed or a variation of some slightly or badly poxed, or a mix of everything and anything.
There is a massive variation in the occurrence and degree of oxidation of poxed bottles, and it gets worse over time. Different wines from the same producer in the same year can be poxed, some severely or slightly or mixed or not. Almost every vineyard and producer had a problem, but not every year and not necessarily the same vineyards. I rememberr one famous producer’s St Aubin being fine but his Bâtard was poxed, from the same vintage. Thus there is no discernible pattern. Its what the Aussies call random oxidation. Or its a pattern that we have yet to discover.
What could possibly explain what seems to be the random occurrence of pox ? What also can explain the variation in the same wine and same case of 6 bottles case when all can be good, bad or a mixture of different levels of oxidation, with some good bottles? Assuming we are dealing with good producers who have good lines, sparge lines and tanks, check filler heads and bottle neck tolerances, measure dissolved oxygen in the tank before bottling and in the bottle after bottling, then the only variable is the cork.
Fèvre had big problems in from memory, vintages 2000 and 2002. But why was 2001 fine? I took samples to their laboratory and we tasted with Géraud Aussendou, head of quality control. We tasted the wines, I think both 2000 and 2002 vintages, marked on a scale of 0 being good, and up to +4, when very good and -4 for the bad bottles. The wines were analysed for free SO2 as we tasted. There was a very good correlation between the colour, taste and score of the wine and the amount of free SO2. The really badly oxidised wines had very low or no SO2. good ones had higher SO2, and the ones in between were pro rata. Deeper coloured wines were more oxidised, lighter ones less so.
A further problem with natural corks, apart from variable porosity, is that they can, when gripped by the jaws of the corker, exude into the bottle between 1-30 mg of oxygen, and each mg of oxygen can destroy 4 mg of S02. So if you bottle with 25mg free SO2 and have 7mg of oxygen exuded into the bottle during the bottling you have zero free sulpur left and the wine can oxidise within months of bottling.
At the July 2021 tasting called Burgfest where I tasted about 300 white Burgundies blind from the 2017 vintage there were 40 or so wines closed with Diam which were very good, with no reduction. But 10% of the wines closed with natural corks had faults of principally oxidation and TCA.
Ask any of the people who have moved to Diam, and who have also checked and improved bottling technique, people like Fëvre and Bouchard Père, Jadot etc. and after adopting Diam they have had no more problems with the pox. Of course if you do not put enough sulphur in the wine it will oxidise under Diam.
While TCA in natural corks is being addressed variable porosity remains a challenge. So far grading of natural corks is done visually. A lovely looking cork could have a chamber burrowed by an insect in it. At present checking porosity destroys the cork. I think they are working on this and weighing corks to help ascertain density. I no longer trust natural corks because they vary so much. A “batch” of corks will come from many different trees and so be inherently variable. If they find a way to ascertain porosity then corks will come back as a good one is of course excellent. The problem is the variability.
Why should corks have become more porous? I do not know but have a theory cork trees are growing faster with global warming and their bark is less dense and more porous. I think some old corks from the 1930/40/50/60s have up to 12 growth rings. Now it is many fewer.
I suggest those who have given up on White Burgundy should try it again when bottled with Diam corks. I think it has solved the problem.
Global warming may produce white Burgundies, and other wines, with less acidity so their are a little more fragile. What many producers are doing now is to reduce the wine’s exposure to oxygen during elevage by bottling after 12 instead of 18 months or moving to larger barrels, 300/600 or foudres.