When I was first deciding on what cork producer to use, I asked around and ended up doing what Ed Kurtzman suggested (always a good thing to do!). Also, I did a lot of research into what changes some of the cork producers were making. This was in 2006/7 and a number of cork producers had changed their processes several years prior to that…not in small part due to the alternative closures impacting their businesses.
One of these changes was lot tracking. Cork slabs are kept together as a lot, from harvest to the final steps of processing. That way, if they discover a lot with TCA (or other) issues, they can trace it back to the source…and if they have repeated issues with that set of trees then they could do something to address it at the source (have no idea what that is tho, if you do let us know!).
Another area of change is in the boiling. Once harvested, the cork slabs are dried outdoor for a bit, and then are boiled (to remove microorganisms in the cork and remove off flavors). About 10 years ago (or earlier?) they started using pressure cookers to boil the cork slabs, rather than boiling at normal air pressure. These are, obviously, huge/massive pressure cookers but the concept is the same (assuming anyone still uses pressure cookers when they cook anymore!). This does a better job of boiling the cork, with less contact time with the boiling water. Also, they filter TCA (and other stuff? but TCA at the very least) out of the boiling water/steam during the boiling process (my understanding is this filtering is more focused on the steam than the water, I believe because TCA is more volatile, tho I’m hazy about this filtering process).
The other area of change is improvements in preventing mold/etc from growing again on the boiled/cleaned.processed corks. Greatly shortening the drying process (aka, the cork is dried in 10% of the time that it used to take). Greater use of ozone and less use of peroxide washes in cleaning the punched corks (not that peroxide isn’t a great cleaner, but it has other issues). Also, some sulfur gas in put into the bags of corks prior to sealing them to help prevent mold from growing (this has always been done, just thought I’d point it out)…note that if you store your corks (in bags) for more than a couple of months (prior to bottling your wine) then you need to inject more sulfur gas into the bags, the same way barrels are sulfured.
None of that was exactly the answer to your question…but it’s what made me feel comfortable going with corks, so it seemed relevant 
. The real answer is that the corks are tested by the producer prior to shipping. I don’t do my own version of these tests, in part because it’s quite difficult to a good/meaningful job of random sampling so the sample can be extracted and tested. For one thing, to get a random/uniform sample, I’d have to open all the bags and handle all/most of the corks…then rebag, reseal and regas (sulfur) them. None of which appeals to me…esp the handling most of the corks part.
Of course, once the wine is bottled I do test the corks (using the open bottle and drink methodology)…and believe me, I’m a diligent tester . Fortunately, I’ve had an incredibly small rate of corked bottles (less than 1%). Still, if you have a bottle of my wine that’s corked, let me know and I’ll replace it.
I’m a fan of Diam corks. Course, back when I was first figuring this out Diam wasn’t as far along as they are now. But I have and am considering them. It’s the Diam 5 and 10 corks that interest me. They have guaranteed Oxygen Transmission rates, in addition to their TCA free (effectively) properties. They come in two different OxTrans levels…one level is (I believe) around the lower end of ‘normal’ corks. The other level is about the same as a stelvin closure. The issue with this lower OxTrans level is closures like these + reductively made wines usually = stinky wines, often times stinky that never recovers. So you need to adjust your wine and/or winemaking to take this into account (for wines where this might be an issue). Unfortunately, the Diam 10 only comes in the super low OxTrans level. The Diam 5 comes in both levels…however the 5 refers to the fact that Diam guarantees the cork for 5 years, which seems like a short amount of time for what I intend for my wines. Many many folks have said that they believe the corks are made to last much longer than this, and imply that the 5 years of Diam 5 vs 10 years of Diam 10 is as much a marketing strategy as anything else. I have nothing against marketing strategies, can’t stay in business without them, but if the Diam 5 really will last much longer than 5 years then I wish they’d say that and figure out another way of differentiating between the Diam product line.
The other thing I wonder about is the issue I mentioned above…about OxTrans of natural corks being much higher during the first year after bottling and the OxTrans drops way way down after that. I believe the explanation for this is during the first year you’re getting the oxygen trapped inside the cork slowly being released into the wine…and after that you’re depending on diffusion through the cork, which is much slower that we might think. Since I make wine in a reductive style (reductive in the sense of very small amounts of exposure to oxygen to retain freshness while developing complexity…not in the sense that I want stinky/reductive wines) this ‘non-linear’ OxTrans property is an appealing quality. Maybe Diam does this as well? I’m not sure. Seems unlikely, but that’s just a guess.
Anyways, none of these seem like unsolvable problems, and might not be an issues depending on the circumstance…so there might be Diam or screw caps in my future. Certainly I agonize over this issue every time I start planning for another bottling. But for the moment, assuming I continue to get very low rates of corked wines, natural corks seem prudent. Feel free to convince me otherwise tho!
Hmmm, is ‘Bigger corks, not bigger Pinots’ a legitimate marketing campaign?
Awesome, love to hear your thoughts when you do pop a cork.
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