Corks, closures and premature oxidation in Burgundy ("premox").

In May 2017, I attempted to gather some information and answers about the possible role of the corks in creating poor seals in the “prem-oxed” white Burgundies, that might have led to premature oxidation, mainly by letting protective SO2 out in the random “bad” bottles. I spoke to the Cork Quality Council twice. Though I never received any real answers to the questions I posed, I did write them out when it became clear that I needed to to have any hope a becoming educated by them. I asked these questions , and post them, so that interested parties/posters can understand the potential role of the corks and seals Dustin Mowe, whose company is one of five founding sponsors of the Cork Quality Council has offered to supply answers to my questions, on another , ongoing thread. Because of its importance in this premox mystery…I think it deserves its own thread.

The written questions I submitted in May 2017 to the cork “industry” in California follow:

• _Cork Questions
• What changed and when, etc.?

• The switch from cork to paraffin was when?
• When did the industry start adding silicone to the mix?
• Did that make the corks more rigid? What effect did it have on the finished corks if not?
• Does the amount of silicone coating vary among the producers…by a lot?
• Does the method you described for both adding paraffin (the football sized block) or used when silicone was added, make for a uniform application on each cork? Or is the amount of each variable? (It is hard to imagine how that works and provides uniformity for the non-scientist like me.) Is centrifugal force involved to make it uniform?
• When and how did cork drying start? And, do you think any of the large producers made any corks too dry? Is there such a point…that the rigidity of the cork is more like a dry sponge than a moist one? How is it done and when in the process?
• If the corks were made more rigid as a result of any/all of the above, what allows the corks to make as good a seal as when just paraffin was used and no drying was done? It sounds like it would be very difficult the more rigid a cork gets.
• Did the producers tell anyone, i.e., allow them to opt out of any of these improvements? (My experience in Burgundy is that the producers had no idea anything had even changed until a few vintages in, when some demanded non-silicone covered ones to avoid rigidity. Could they still get them?

• Does silicone coating or drying contribute more to a rigid cork?
• I read today that an estate in Chablis which switched to DIAM or screw top…or both…had NO issues with those closures, but in vintages where real “corks” were used, there were lots of problems with prematurely oxidized bottles within given cases.

• I realize that transfer of oxygen is much better with real corks, and that is a reason to use them, but has your industry ever done studies on the rates of failures, i.e., not due to TCA…with bottles under cork, particularly from the mid-90s?
• Yesterday, I watched several YouTube videos on cork production…very educational. Are there any you recommend that address/show the changes in methods of production (i.e., coating and drying) and how they were done?

• Clearly, something changed dramatically with White Burgundy (WB) and the rates of premature oxidation from the mid-90s vintages…and some producers had lots of it…and others not so much…and it often varied from year to year at any given estate.
• So, the wine and the closures are the likely candidates. I know nothing much about winemaking, but I’ve had 20 year old WB recently that were flawless…and under cork. So, the wine is, IMO, fine, even if more vulnerable. And, from a case of them….4 were totally oxidized.
• I am not trying to indict the corks, but to try to understand the variables between a good bottle of a particular producer’s lot in a given year…if the wine is all the same. (I know oxygen rates are variable…with the ullage and other oxygen, but….my guess is that the variations were MUCH more in the ‘80s when this problem never occurred…though it did somewhat in the 1989 vintage.
• And, as I told you one producer showed me in 2007 that with the good bottles, the SO2 levels were the same at bottling; in the bad bottles, it was all gone. You said that the oxygen would essentially “eat up” the SO2, but…why did this almost never happen before the ‘90s? Could the SO2 “escape” with a poor seal at the bottle neck…or is this not possible? Would oxygen come in with a bad seal? Or SO2 go out….or both?
• Does the cork industry have any research it did/does about its possible involvement in the prem-ox issue? If someone is looking to do some, I have a perfect producer in WB to use…….He only sells his wine when mature…it sits in refrigerator temperatures until then (thus impossible to taste in Meursault), so he releases at 10 years, white and red, at the earliest. And, since I last visited, he has had a stroke …and since he single and has no heirs….he probably would be happy to cooperate. (I used to know his importer into the US very well and could contact him if your “people” wanted to check it out. My idea would be to see what’s different with bad bottles…even if kept in pristine conditions. (I have no idea whether his were or were not affected by the premox.) Just an idea.

• My own informal “survey” over the last 20 years of WB…I stopped buying in 2007; my wife said I was too old and had too much wine…and I’m glad she did. My survey convinces me that when there is a good bottle, the cork, at least part of it near the headspace, is as moist as always, if only on the bottom? (And does the bottom of a cork get coated…or just the sides?)
• I find this fascinating, though I don’t think the issue if as much one of science as it is common sense and bad closures. So, I really appreciate your thoughts here.

_

Did they respond in full ?

I will try to answer some of your questions below. hoping i am quoting properly so that you can see which questions i am attempting to answer.

There was no “switch” from cork to paraffin as you state. In ancient Greece, amphora’s were sealed with cork covered with ‘’resin’’. A cork that has nothing on its surface and is inserted into a bottle will both leak (at cork and bottleneck interface) and be nearly impossible to extract.

At the end of 19th century appeared the first reference to paraffin and paraffin wax Used on surface of cork stoppers sealing wine. The use of paraffin as a surface coating of cork stoppers Became “the standard” in the 30’s largely driven by the French market.

The use of Silicone on top of the paraffin occurred in the 70’s first introduced by cork companies in Germany and in the mid 80’s paraffin with silicone oil became the standard worldwide including the USA. Both products act as a lubricant but paraffin has as a very important role of “waterproofing” of the cork.

The cork needs something on its surface in order to allow it to insert and extract. in addition, paraffin makes the cork more hydrophobic and helps create a better seal between cork and bottleneck interface. The silicone is usually a very small amount and only is there to make the cork more slippery (ease insertion and extraction). A cork only coated in Paraffin is very hard to extract and risks bottleneck breakage. A typical extraction value for wines bottled today with 49x24mm natural cork with standard coating (paraffin/Silicone) is around 23 daN and a cork that only has paraffin on it would be around 50+ daN for for bottle at room temp and even higher if cold.

Yes, every supplier has their own proprietary way of coating cork. However, your reference to “football size blocks” is a very old way of applying paraffin and was most likely last used in the late 80’s or early 90’s at the latest. Most suppliers use an emulsion of paraffin and a light spray of silicone oil. Techniques for application as said vary but there are tests we do to insure uniform application of the coating on the stoppers.

i am not sure how to answer your questions about “cork drying”. When cork is produced, they are washed in either water/metabisulfite or peroxide solution to disinfect the surface of the cork. Once the corks are washed they go through a cork dryer to bring the humidity down from 20% to around 6%. Humidity is the enemy of cork. We work hard once the cork is stripped from the tree to keep humidity levels low during the whole cycle from tree until we are shipping to a winery finished product in order to insure mold/TCA/TBA etc is not formed (especially in transport from Europe to USA). We want the cork below 5% because it spends 6 weeks on a boat to get to USA and when it arrives we bring the humidity up to around 6-7% before shipping to wineries. In Europe (it seems you are mostly talking about burgundy) i cannot imagine the cork is ever below 5.5 or 6% and a cork is not “dry” unless it is below 4% (A cork feels pretty elastic over 6 and more rigid at 4%).

There has been a lot of work on the Burgundy premox phenomenon by the cork industry. some years ago many producers blamed the silicone (sounds like you talked to one of those guys) and therefore asked for no silicone on their cork - this did NOT solve the issue and only gave a whole host of other problems (mainly extraction).

then they thought it was a density issue and asked for larger diameter cork (25 or 26mm instead of 24mm) and a more controlled density (weighting of each cork). this did NOT solve the issue.

then they asked for no peroxide washing on the cork - only a water bath. this did NOT solve the issue.

There has been nothing that was “changed” by the cork industry during the height of the “premox” era that has been identified as the culprit and multiple trials were initiated.

Dustin:

Thanks for your answers. I appreciate them.

The “football sized” block of parrafin was something that the Mr. Weber told me to imagine, when I was having trouble doing so. He said it was like a clothes dryer with the parrafin being put in in block form and flying around just like a clothes dryer. At some point, he said, “silicone” was “added to the mix”…for easier extraction. How that is done physically vis a vis the parrafin application process, I never got to , though I wanted to know. How IS the silicone applied? same way? or totally different, more consistent process that what Mr. Weber described the parrafin process as…stuff flying around willy nilly? And…when did silicone get added to the mix and sent out into the market? That’s the only important date here…when silicone was added to parrafin in any significant number of corks into the market? They certainly became more rigid at that point, it seems.

I well understand the benefit of silicone in helping a cork, particularly an older cork, siding out. It seems like the “slipperiness” ,ie, friction with the silicone would be about 50% of what it would be with just parrafin? The benefit is not of any interest; the regularity of the corks and their rigidity facing the bottle necks is the issue. Is it a variable? (It’s hard to see that it can’t be). It seems you are confirming that the cork , therefore, became more “rigid” when silicone was added to the mix/applied to the corks with the parrafin…(Was it mixed in or done as a separate process, with different machinery…after the parrafin was applied?)

Then , there is the issue of when “kiln” drying became the norm for corks. Given that corks are a natural product and, therefore, irregular, it is difficult to imagine that kiln drying would not result in harder/more brittle corks in the same variable array. I assume that the parrafin was then applied? and then the silicione? to the dried corks? or in some other order.

So, the question is whether the premox started at a time of a “perfect storm” of added rigidity for the corks: from kiln drying…then adding silicone to the parrafin-coatings…resulting in irregular rigidity…that all three would combine to create…but…not necessarily…just the drying or just the silicone… That’s what I’m attempting to fathom here…how the corks with both kiln drying’s rigidity…and then adding the rigidity of the silicone…could not result in lots of irregularity…ie, variablity…at the bottleneck where the seal is made…How can anyone rule this out is my question? Given that the kiln drying and silicone are imposed on a naturally irregular prodcut like cork? How could the rigidity actually improved the regularity of the naked corks…when they are already irregular? (My understanding is that the parrafin, thinking candle wax here…actually made them more regular by acting as a sort of grout between the cork and the bottle neck…albeit creating extraction issues.

So…I ask…when were the corks which had all three processes: kiln drying, parrafin and silicone…or if ever…just kiln drying and silicone…put into the Burgundy wine market in significant numbers…? Did this first happen in the early '90s…?

And…what other variable than the corks and , therefore seals, can you surmise would effect variable numbers of bad-- and good-- bottles within any given group? Particularly anything that changed about the same time as the “premox” first showed up in Burgundy…very early '90s…??

If the wines changed too much…there would not be so many good, fine bottles of WB. So…something else changed that resulted in variability? And…there is no reason to believe that the bottlenecks themselves changed to such irregular quality to account for the bad bottles, but still have the good bottles.

I am not surprised that none of the things you describe “solved” the problem…IF the problem is a poor seal due to rigidity from the kiln drying/silicone coatings…to me, it might just point to that as the problem.

Again, Dustin, thanks for your civil answers… I’m hoping we can have a civil conversation here…I have no “horse” in this race. I am not that knowledgable about wine bottling…and , frankly, am not that interested. But, I am perplexed that 15 years after the plague did its evil…no one can figure out the reason why the plague of premox affects any given number in a a variable/random manner.

thanks

stuart

Stuart,

between this thread and the other, you keep asking the same questions so it is quite difficult to carry on this dialogue. you ask “how is silicone applied”? i answered that above (it is an oil that is sprayed)… It is a second step in the process of coating the stoppers (first is paraffin and depending on technique sometimes we go straight to silicone or sometimes we wait till the next day to do the silicone). We have some slightly different methods/formula’s for different customers / quality of cork (usually matched to quality of wines they are sealing).

you keep insinuating whatever we did to the cork made them more “rigid” (in fact you refer to cork becoming more rigid 18 times in two posts!!!). The only way i know a cork to become more rigid is lower humidity. Paraffin and or silicone does not make them more “rigid”.

You also ask again about coating with silicone only and i know no producer of natural cork stoppers that does or has ever used silicone only to coat stoppers. You would have problems with absorption and capillarity (=leakage).

regarding your questions of timing of when cork would have been washed, dried and paraffin/silicone treated - i believe it was in the 70’s (inline with when we started using paraffin with silicone). Only real change since then was a shift to peroxide washing of the stoppers (mid 80’s but not a lot of burgundy used these because the color of the cork changed and burgundy likes a more natural look) and later on refinements of the methods of washings and coating application.


Dustin

How IS the silicone applied, Dustin? You keep saying it is “sprayed” on as an oil. But, what is the method? Like a car wash? Hand? Machines? Do you have a video you can share? I guess I’m trying to understand the quality control issue and how it is addressed for consistency.

Something makes some corks more spongy and some more “rigid”. The silicone does not add to the rigidity, you say? Meaning it has no effect on the seal…for better or worse…than a cork merely coated in parrafin? That’s not what I had thought…So, maybe I’m misinformed. I was shown corks with parafin and corks with silicone…and could squeeze the latter pretty easily and compress them…but not the siliicone ones?

When did “kiln drying” begin on an industry-wide basis? Given that corks are a natural , ie. variable product…how is drying some too much avoided…? or , at least selling those dried too much? Is there some safeguard?

In sum, it seems that you are saying that nothing changed in how corks were finished…ie, dried, coated after the late '80s? Again, contrary to what I’d been told, but…I can’t argue.

All I remember is that two producers showed me corks…and said to try to squeeze them…they were so rigid , I could not, so…one has to wonder how they expand to form a good seal with the bottle.

I still think analyzing the prem-oxed bottles’ corks and comparing them to good bottles’ corks could reveal something.

Otherwise, what do you you think the variable could be that makes some good and some bad…if not the seals/closures? Serious question…not rhetorical.

Thanks again. I’m learning, I think.

Indeed this would be interesting.

There is clearly variation from bottles of the same wine, same vintage and within the same case.

It might show no difference in the permeability, it might show no difference in the level of coating/treatment. All such negatives would still be of use in narrowing down the problem. Just as differences in permeability doesn’t necessarily mean cork is the cause, but rather the reason why some bottles are badly affected and others unaffected.

I don’t know how soon after opening such analysis would be needed, but this does strike me as a very useful analysis that could potentially help understand this problem, that is still unsolved more than 20 years after it first came to light.

coatings are sprayed via a spray gun just like paint gets sprayed. for Portocork, a robotic arm with a spray gun enters the coating drum as it rotates and a set level of coating (flow meter controlled) is applied to all the cork as they tumble.

Something makes some corks more spongy and some more “rigid”. The silicone does not add to the rigidity, you say? Meaning it has no effect on the seal…for better or worse…than a cork merely coated in parrafin? That’s not what I had thought…So, maybe I’m misinformed. I was shown corks with parafin and corks with silicone…and could squeeze the latter pretty easily and compress them…but not the siliicone ones?

coating has ZERO to do with a cork being spongy or “rigid”. A cork that is easier to squeeze than another is most likely due to humidity (most likely) or density of said cork.

When did “kiln drying” begin on an industry-wide basis? Given that corks are a natural , ie. variable product…how is drying some too much avoided…? or , at least selling those dried too much? Is there some safeguard?

Drying of the cork has been happening since at least the 70’s (i only know this date because i have seen a dryer that was from the 70’s in cork plants). when cork are dried it is done in batches just after the washing cycle (usually 40-90,000 cork at a time). when they go to the drying they are all very close in humidity since they were just washed in a bath together for 60-90 minutes. Same for when they come out of the drying. you dont have cork at 13% and some at 6. you could pull 20 random cork from the drying cycle and you would have for example a range of 6.1-6.5%…very little variability.

In sum, it seems that you are saying that nothing changed in how corks were finished…ie, dried, coated after the late '80s? Again, contrary to what I’d been told, but…I can’t argue.

All I remember is that two producers showed me corks…and said to try to squeeze them…they were so rigid , I could not, so…one has to wonder how they expand to form a good seal with the bottle.

Way way too many variables to hypothesize why. I’ll give one example - a cork that has been inserted without vacuum (creating positive pressure inside the headspace) will be much more spongy when extracted than a cork that was inserted with proper vacuum at bottling.

still think analyzing the prem-oxed bottles’ corks and comparing them to good bottles’ corks could reveal something.

Otherwise, what do you you think the variable could be that makes some good and some bad…if not the seals/closures? Serious question…not rhetorical.

Thanks again. I’m learning, I think.

indeed i agree that this analysis can be helpful in understanding the issue.

Well, as I said somewhere else…maybe to Peter Weber, there is a perfect producer in 'Burgundy, Robert Ampeau…that the cork people can get intact cases of relevant white
wines, to buy and try and then look at the corks and SO2 levels vis a vis what the good ones have in them. Let me know…if there is any interest.

Though I continue to believe that the seal is the only sensible/logical explanation for the variability of bottles (which is the whole premox-plague: the variability of bottles that turn bad and others don’t)…and that the rigidity of the corks is the likely culprit, I have appreciated your cordiality on this subject and informative posts. Though I continue to believe that the seals, and not the wines are what make some wines “bad” in a given case, you have certainly changed my thoughts about recent changes that I thought had resulted in too-rigid corks. The question remains about whether the corks are or are not “too rigid” to make a good seal…and, I guess…manufacturing variations in the bottles themselves which might prevent a good seal.

I guess I’ll look to see how alternatives to corks have fared with the “prem-ox”…though you’d think this would be widely available by this time.

Let me know if you or the “industry” decide to contact Ampeau for guinea pigs…under natural corks…with bottles stored in pristine conditions since bottling.

It is truly disheartening that the problem remains caused by mysterious variables…after all this time. But, I think it does.

I’ve had oxidised Ampeau, but then both were late 80s wines - so not pre-mox, per-se…

Off the main topic a bit, but this caught my attention: if humidity is the enemy of cork, why is there such strong conventional wisdom that you need humidity to maintain cork’s integrity while in the bottle?

Not Dustin (obviously)…but…clearly at some point, humidity is needed. Otherwise the cork is like a dried out sponge…and makes a seal the same way…

The “industry” seems to have decided that for TCA/mold humidity is the enemy of the people, so they’ve tried to dry them out in kilns. I have a hard time understanding how a natural product, with attendant variability, including ability to maintain humidity, can be made uniform for making seals, if the dry cork cannot always make a good one. (I had thought it was the silicone which added rigidity; I have to assume that if it doesn’t, then the kiln drying is what makes them more rigid… a la a dried out sponge. A moist cork would clearly make a better seal, I 'd think. Do you?

Not suggesting their '90s whites are impervious, just intact and kept at the winery in many cases. A purely controlled sample for the cork investigators…or anyone.

No recent experience with the estate…last visited in 2007. Just hard to think of a better time capsule for investigation of this issue…and the closures’ input.

Love the conversation and the information - thanks to all involved and really enjoying the give and take.

As far as humidity and moisture goes, when I worked elsewhere, we ran a moisture reading of corks before they were heading into the hopper on the bottling line. If the number was either too low or too high, we were concerned - too low and the cork might be too brittle and therefore break easily; too high and it might not form the right seal.

Different cork companies provide different ‘parameters’ that one should expect when receiving their corks. I remember one company who always suggested much higher moisture levels than other - and felt this helped their corks. We never used them but others did - would be curious to see how these held up over time.

Dustin - do you still monitor moisture in each cork lot and do you have upper and lower limits you are looking for? Have these changed over time?

Cheers.

FWIW, I opened and poured Ampeau’s 1993 Puligny Les Combottes at a largish Burgundy event last spring. No premox at all, and it was a splendid wine, enormously rich, dense, and deep, with a beautiful bronze golden hue. Pretty much outdid all the other white Burgundy (including some 1er Roulot), with the exception of some Coche Les Caillerets.

Stuart, that’s just begging the question: you can’t answer my question of why humidity is bad for corks before being used, but good while in use as a closure just by saying it’s necessary to function properly as a closure

What i am referring to above is the storage of cork before usage. Whether it be raw cork planks (pre-punching) or finished stoppers they can easily be prone to microbiological growth if the humidity is too high.

For cork storage you do not want a cork above 7% humidity (we ship them from Portugal around 4.5% and bring up the humidity before shipping to wineries). For cork “usage” you want a cork around 6%. if the cork is too moist it gives fits to the guys running the bottling lines.

too low humidity and the cork is not as “forgiving” (more prone to chipped edges and such during bottling). Too high and you have a lot of insertion variation and if you have a multi head corker it can give you fits. We check the corks a few times in process and wont ship an order unless it meets our spec of 5-7.5%. In my opinion a good moisture at bottling is 5.5-6.2.