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March 22, 2011


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Speck is only my favorite of the cured Italian pork products. http://en.wikipedia.org/wiki/Speck

It will be interesting to see how the same wine tastes in five years with a screw cap vs a bottle with a cork. I would love to be there for that tasting!

I thought we all grew up singing that classic song:

"Once there was a Dutchman, his name was Johnny Roebeck, and he was a dealer in sausages and speck..."

Tom, I'm curious, in your research did you find that wine makers using screw cap closure also tend to adjust preservatives such as reducing the amount of potassium metabisulfite to compensate for the presumable more effective closure?

Kevin: Yes, at least Kareem Massoud does. This interesting tidbit was unfortunately buried near the last paragraph of the piece.

I have found many cases where my nose hairs have been practically burned off by the amount of SO2 in screwcapped wines. I think in many less careful winemakers continued adding the same amount of sulfites after switching from cork to screwcap, operating as if nothing had changed. Changing the closure is a big adjustment, and measures should be taken to avoid problematic outcomes, for example the management of sulfides in the cellar, as Kareem pointed out.

Lenn: Interesting. There are "meaty" thiols as well, like 2-methyl-3-furanthiol, which would be preserved in the same way as the "fruity" thiols.

This one looked interesting, too:
"Impact of Oxygen Dissolved at Bottling and Transmitted through Closures on the Composition and Sensory Properties of a Sauvignon Blanc Wine during Bottle Storage"

It was interesting to see that the Saranex 38 liners have polyethylene as the wine-facing layer while the Saran-Tin liners have polyvinylidene chloride (over the tin) in contact with the wine. (It seems like polyethylene would have less chance of degrading into something unpleasant over the long term than would polyvinylidene chloride, but it is also more oxygen permeable. Though in the dark without much oxygen, they're both probably fine for a long long time)

Hard to correlate btw screw caps and quality in this instance since the Massouds have been making great wine at Paumanok for many years using corks and are now doing the same using both closures. Could a fabulous home-cooked meal from Ursula have anything to do with the result? Lenn plz come clean on this.

Nice post Tom, thanks!

Great post. I'm a little curious about whether they mentioned copper additions in an attempt to avoid reductive issues. A lot of winemakers that I talk to about bottling reds under a screw cap feel that this is all but necessary.

AdamS is right...about Paumanok making good wines for years. Unfortunately, I have yet to experience an Ursula-cooked meal!


I'm not a polymer chemist, but I agree that I'd prefer to avoid organic halogens in general. I guess time scale is the most pertinent question. If a Cl* radical breaks off once every 10 years or so under pHs between 3-4, then it's probably not a big deal.

Then again, the polymer that's in contact with the wine is one of only about a million other things to consider in choice of closure. One could write a whole book on closures (and my wine science idol, Jamie Goode, actually has). In general, polymer-based seals seem to be quite oxygen permeable, including Saranex screwcaps, Vinoseal, et al. in addition to synthetics.


Copper is just one tool for managing sulfides in the winery. It would be irresponsible for a winemaker to, say, add the legal limit of copper for any wine that will be put under screwcap. In fact, as I mentioned there are lots of "good" thiols, which would also be stripped out with the mercaptans and H2S after a copper addition.

Also, disulfides are NOT susceptible to removal with copper. Disulfides can reduce over time to form mercaptans (a potential cause of "reductive" problems with screwcaps). In fact, if there were residual copper in the wine and mercaptans arose post-bottling, it could lead to a nasty black precipitate in the finished wine (copper sulfide). Plus, copper and other heavy metals are closely regulated... because they are toxic in high doses.

So there are a lot of things to consider while contemplating a copper addition. The impression I got from Kareem is that monitoring fermentations for H2S production (i.e., preventing formation of too many mercaptans/disulfides in the first place) is far more important than prophylactic copper additions.

"The impression I got from Kareem is that monitoring fermentations for H2S production (i.e., preventing formation of too many mercaptans/disulfides in the first place) is far more important than prophylactic copper additions."

Tom, exactly. Sulfides are first and foremost a winemaking problem/issue/complexing factor (depending on their kind and severity and depending on one's style and palate). The fact that screw caps make a tighter seal than other closures by definition means they create a more reduced environment for the wine. And so logically it is correct that the more reduced environment will exacerbate the formation of sulfides, however, it is far less important than making sure your wine is free of sulfides in the first place (of course it's impossible to be 100% certain of this). Sulfides are not really a closure problem.

Thanks both Tom and Kareem for your responses. I have little formal chemistry training but this is a topic that I find both fascinating and pertinent. I agree that preemptive copper additions are irresponsible at best (seems to be a "make the foot fit the shoe" mentality), which is why I posed the question. From what I've heard and read, copper additions (when bottling under screw cap) do seem to be a wide-spread practice. Surely copper has an appropriate place in the winemaker's tool kit but I wouldn't be surprised if it were abused (knowingly or not). Beyond preventing sulfides from forming in the first place (or trying to), what does a [responsible] winemaker do to prevent issues when bottling in a reductive atmosphere? Kareem, maybe sulfides are not a closure problem but I would have to assert that reductive issues certainly should be (and are) considered as part of the closure decision.

I think screw caps have an important role in the industry but reductive issues are one of the concerns I've heard from many winemakers when considering them. It would be great to see them viewed as completely viable closure option and clear that hurdle.


"[M]aybe sulfides are not a closure problem but I would have to assert that reductive issues certainly should be (and are) considered as part of the closure decision"

I totally agree. As for managing sulfides, Kareem could probably speak to this better, but generally H2S arises from two places: (1) reduction of sulfur residues on grapes and (2) poor yeast nutrition.

It seems odd, but yeast produce more hydrogen sulfide when they are starved of nitrogen. Essentially, when there isn't enough yeast assimilable nitrogen (YAN: ammonia, amino acids, etc.) to produce biomass, the yeast starts to recycle its own amino acids. Sulfur-contaning amino acids like cysteine and methionine create H2S when they are recycled in this way.

It was common advice from Cornell (especially in the Henick-Kling era) to add the legal limit of DAP (diammonium phosphate) to fermentations to ensure adequate yeast nutrition. Nowadays, we know that adding *too much* DAP creates its own problems, including microbial stability issues, increased biogenic amine production, and the possibility of creating too much biomass... which could lead to the same sulfide problem you had in the first place. Complex fermentation aids like Fermaid O, etc. can circumvent some of these issues.

Testing for YAN is relatively straightforward if you have the proper (i.e., very expensive) equipment. The NYS Wine Analytical Laboratory will do these tests as well.

Apart from all the technical checmical aspects that the post itself and comments deal with, there is another much more important side to the closure debate, namely the environmental question.

I'm sure you all know already that the aluminum mining and fabrication process is one of the most polluting that exists; and that cork farming is one of the most sustainable and beneficial, both enviromentally and socially (and culturally too, if you want).

I'm perfectly happy to bear the 'cost' of sending a corked bottle back every now and then, rather than conuming yet another aluminum or petroleum-base closure, and adding to the planet' environmental problems and leaving the mess for our children and future generations to clean up.

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