Education,Wine,Wine Accessories

UC Davis: Taste will tell the tale on wine bottle closures, or will it?

I got this Email press release, and I’m not going to try to reinvent the wheel here. It’s going to be below my own personal intro… I’m always fascinated by the subjects of universities’ studies, regarding what’s happening in the world (in this case, the world of wine) worth fully investigating.

Can we tell the difference in taste between a bottle with a screwcap and a bottle with a cork in it?

Probably not, unless the bottle is corked.

I just returned a corked bottle to my local grocery store. The TCA (trichloroanisole) was horrific. All the salesman would have had to do was to have pulled the cork out of said bottle, and the smell of a damp new England basement would have flooded his senses and turned his stomach upside down and backwards, like it did to me when I opened it.

Instead, he just looked at me like I was from Mars. (“This in the heart of wine country?” I thought to myself. Shows how naive I am, thinking everyone around me has absorbed everything I have in the last 20 or so years. It was a good wake-up call for me.)

I had to guide him to where the replacement bottle was, because he wasn’t the wine steward, and any wine department is flooded with wine products, overwhelming anyone not stocking those shelves. When we reached the location, he then began fumbling for a bottle that was “on it’s side” directly below what I had pointed out as, “It’s right here.” The one of my purchased brand of Torrontés had corks in them, as I’ve described. That brand only had a few bottles left that were standing up in this wine rack. The closure colors, for what he was pulling out, however, were a completely different color, and they were screwcaps to boot.

“Ah, no TCA there,” I thought to myself. So I explained, “It’s not about the cork, it’s about the TCA,” digging myself even deeper into his confusion.

I said, “I’ll take this bottle right here,” now leaving him totally confused, because he was looking for a bottle that wouldn’t have a dry cork. I’m sure he was thinking to himself, “I thought she said it was about the bottle being ‘corked.'”

And, by the way, screw caps cost wineries more than corks do, including having to buy more equipment to get the closures installed properly. So, it makes sense to me that this would become a study… Also, look who’s paying for the study (very bottom of this page)… The same guys who consider themselves pioneers in the use of screwcaps by a higher end wine brand. In my humble opinion, the use of screw caps has and continues to cost them a bundle, and years later it’s time for them to find out whether or not it was worth the innovation. Meanwhile, the cork trees in Portugal are having a good laugh… Or, are they?

Now, the study…


To help winemakers determine the best caps for their wine bottles, researchers at the University of California, Davis, are studying the performance — specifically the variability — within different types of closures.

Their goal is to determine whether consumers can taste the difference in wines that are bottled and capped exactly the same — a difference that could be attributed only to variation among each type of wine closure.

The researchers — including a wine chemist, a medical radiologist and a biomedical engineer — are evaluating 600 bottles of Sauvignon Blanc wine, each sealed with one of three different types of closures: natural cork, screw caps or synthetic cork. The study will monitor changes in the wine during aging, culminating in a sensory evaluation to determine if wine experts and consumers can taste the different levels of oxidation that occur in the wine due to variability within each type of closure.

Oxidation, or exposure to oxygen, is the most important factor in wine aging, according to wine chemist Andrew Waterhouse, a professor in the UC Davis Department of Viticulture and Enology. But too much oxidation can cause a loss of color, flavor and aroma.

“Our goal in this study is to determine if individual bottles might be getting a lot more or less oxygen — and therefore aging at different rates — as a result of the variation in the closures used to seal the bottle,” said Waterhouse, who is carrying out the study with UC Davis undergraduate student Jillian Guernsey.

“Ultimately, when all of the data are in, we won’t be declaring that one type of closure is superior to another. Rather we’ll be giving winemakers information about the variability of each type so that they can determine which is most appropriate for use in bottling their wines,” Waterhouse said. “If variation is high enough for consumers to notice a difference, we will work with the industry to help find ways to manage the variation so that consumers receive the wine as it was intended.”

The Department of Viticulture Enology, the largest and most comprehensive university wine program in the United States, has been at the forefront of international grape and wine innovation for 130 years. It continually partners with industry to develop practical solutions to problems that are of concern to winemakers and consumers.

The researchers have included a novel step in this study, using medical imaging technology to obtain a baseline evaluation of each of the corks. To do this, they teamed up with John Boone, a radiology professor in the UC Davis School of Medicine and an internationally known expert in designing and improving computed tomography scans for breast imaging. Boone, who also leads the cancer imaging research initiative for the UC Davis Comprehensive Cancer Center, used a new CT scanner, which he had invented, to obtain images of each of the 200 natural and synthetic corks.

David Fyhrie, a professor of biomedical engineering who also holds the David Linn Chair in Orthopaedic Surgery in the UC Davis School of Medicine, will analyze the images to look for differences in the internal structure of the corks.

All of the 600 bottles of Sauvignon Blanc wine are being stored in a temperature-controlled wine cellar at 20 degrees C (68 degrees Fahrenheit). Each of the bottles will be tested for darkening in wine color at three-month intervals during the 12-month study. Earlier research in Australia has demonstrated that the color of white wine is a reliable indicator of the degree of oxidation.

The researchers will use specially modified spectrophotometer devices to analyze the wine color in the bottles without opening them. Clear glass bottles are being used to facilitate color-based monitoring of oxidation based on color change.

At the study’s end, the 600 bottles will be divided into three groups, based on whether they show high, average or low color change. The wines with the most and least color change will be opened for chemical analysis and sampling by members of a sensory panel, who will try to identify differences in taste and aroma between the most- and least-oxidized wines. That sensory analysis is expected to take place in during the summer of 2013.

Waterhouse said that there is also considerable interest in the comparative sustainability of wine bottle closures.

“All wine closures are made with sustainable practices, and to date I have not seen data showing a definitive difference between them,” he said. “It’s important for wine consumers to remember that the bottle closure is a very small part of the wine package’s environmental footprint,” he said.

The study is supported in part by CADE Winery of The PlumpJack Group. PlumpJack Winery pioneered the use of screw-cap closures for ultra-premium wine more than 10 years ago.



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6 Responses to “UC Davis: Taste will tell the tale on wine bottle closures, or will it?”

  1. Jo
    You are being a bit disingenuous, or snarky, by associating only ONE of the sponsors of the study with probable outcome. As you mention that Plumpjack is only “in part” a sponsor, there will likely be no “cause and effect” here.
    Knowing the players here, I think we can expect a fair and enlightening study, which should answer a few key questions about this fundamental issue. I agree, a lot of $$ rest on what the study might answer. Believe me, the Cork companies have spent fortunes on studies to attempt to sway folks in their direction. And to some degree, new technical processes have helped cork manufacturers to decrease taint issues over time significantly.
    For me the bigger issue is that inherently, cork is an organic substance, and therefore susceptible to bigger, systemic problems in a bottle resulting from shrinkage, for example, which leads to oxidation. It can also absorb other odors as well, potentially tainting the wine inside.
    Still, after having a corked bottle of 1995 Mouton Rothschild the other night at a tasting, the problem will not go away easily. In the end it’s a QC issue that screwcaps address the best today (at least as far as I can see), though the environmental impact of corks vs screwcaps is a legitimate discussion

  2. Jo Diaz says:


    The sponsor is the sponsor… that was the only one supplied in the press release from UCD. Had there been others, my opinion would be the same.

    IMHO, what I wrote is neither disingenuous nor snarky. It’s the reality of the world we live in, after my years of experience in these matters… So, maybe I’m more disillusioned and not as naive as I was when I was much younger and wearing my rose colored glasses.

    Best and cheers to you, too.

  3. Nat Scott says:

    I read your stuff often and always find it interesting and informative. I was under the impression that most corks were more expensive than screwcaps and it was only the cheap technical corks that cost less. TCA is not only a cork problem as it can be found in wineries and can live up to 2 cm deep in oak barrels. Also the reductive problems with screwcap are only now starting to come to light. Please let me know if I have been ill informed. I have no dog in this fight as I think that there is room for both in the market.
    Thanks and look forward to reading more from you.

  4. Jo Diaz says:

    Hi, Nat and thanks for weighing in.

    It was while I was working with Foppiano Vineyards that I was told that screw caps cost them much more than corks did. I didn’t realize that, either, but then I never had to buy supplies for making wine.

    Seeing what this study brings is going to be interesting. It’s either going to be bragging rights for Plumpjack; i.e., “It doesn’t make a bit of difference, and we were way ahead of the curve as industry innovative leaders…” Or, it’s going to be “It does make a difference, and we were way ahead of the curve as industry innovative leaders.”

    If it makes a negative difference, we’ll probably never hear a word about it in the future…

  5. They really need to also check any absorption of plasticizers by the wine. Saranex which is used in both types including the extra tin lined ones is not used in Saran wrap anymore because of plasticizer absorption by food. Wine has a low pH, sulfites, and alcohol to aid as solvents so I can hardly believe the absorption would be less than any food. I don’t think beer is sealed with saranex anymore which is why the big breweries date their beer now due to less shelf life. Wine is much more likely to be laid on its side than beer. Why is this not being researched?

  6. Jo Diaz says:

    Keith, you raise some really great points… Build it, they will come, and when thry’re all sick, we’ll figure it out, right?

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