Corks, screw caps. synthetics: Can tasters tell by tasting?

[Robin Garr]

Very interesting news release from UC/Davis. The results, when they come along, should be fascinating.

University of California, Davis
September 20, 2012

CORKS AND SCREW CAPS: CAN WINE CONSUMERS TASTE THE VARIATION?

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.

About UC Davis

For more than 100 years, UC Davis has engaged in teaching, research and public service that matter to California and transform the world. Located close to the state capital, UC Davis has more than 32,000 students, more than 2,500 faculty and more than 21,000 staff, an annual research budget that exceeds $684 million, a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more than 100 undergraduate majors in four colleges -- Agricultural and Environmental Sciences, Biological Sciences, Engineering, and Letters and Science. It also houses six professional schools -- Education, Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.

One would have thought this study would have been done years ago with so many screwcap bottles on the market today.

I would say the “studying and researching” started when Louis Pasteur coined the phrase “oxygen is both friend and foe to wine”.

Salute

I've had several producers I import change from cork to screwcap, and you can certainly tell by tasting when you taste a number of bottles: all the bottles from one batch taste the same. What a concept.

Oliver wrote;
I've had several producers I import change from cork to screw cap, and you can certainly tell by tasting when you taste a number of bottles: all the bottles from one batch taste the same. What a concept.

That itself doesn’t tell us much, or something that we don’t already know. This study most likely would ask the participants very “basic” questions like “rank the wines” in the order you like them and try to identify what enclosure was used to “seal” which given glass of wine. There is a lot of research and studying going on, but the biggest obstacle is trying to figure out the most appropriate and accurate way of measuring oxygen transmission rate (OTR). In this study, instead of trying to give a “value” for OTR, they would look at one aspect of oxidation (“browning” of a white wine, and measure it through a clear glass wine bottle) and try to determine the rate of this “browning” under a given enclosure.

Salute

They are measuring variability within each closure type. Many different iterations of the same wine with the same screw cap brand would presumably be tasted, presumably in difference testing (either pair testing or triangle testing) to determine if variability exists, and the extent of variability. Then the same would be performed on controlled samples with cork, or controlled samples with artificial corks. They do not seem to be asking which closure is better, but rather which closure is most consistent. Of course, in order to do this in an all-encompassing manner, one would need to have a large sample population from each of the manufacturers and styles within the group, and in the case of natural cork, with grades as well.

Let us suppose that we hypothesize that screw caps will provide the least variability, and we conjecture that no more than 1 in 200 samples will be judged significantly different, because minor flaws were detected in .5% of the samples, and yet we find that 2% are judged significantly different. Are we judging the screw cap integrity, the difference in valve fill level, the differential turbulence inherent in the filler valve, variability in the purging of the bottle, the closure vaccuum variability, differential in roll pressure, or any other equipment variability rather than closure variability? Presumably, the plastic membrane/sealing surface is uniform in composition. Unlike cork, a biological material with differences in porosity and composition from cork to cork, probably difference of uniformity of paraffin coating and silicone, as well as potential difference sin flora from cork to cork. Add to that similar equipment variability.

I am sure they will limit this to one set of closure equipment per type (perhaps using single-head packaging units to minimize equipment variability), and standardize each type of closure, eliminating variables and asking and answering a basic question, rather than an all-encompassing question. They cannot afford to show preferences in equipment or closure supplier. Such questions will be left to the winemakers to evaluate on their own, as well as evaluating the tradeoffs between consistency on the one hand and potential beneficial effect to the wine on the other hand.

Oliver wrote;
I've had several producers I import change from cork to screw cap, and you can certainly tell by tasting when you taste a number of bottles: all the bottles from one batch taste the same. What a concept.

That itself doesn’t tell us much, or something that we don’t already know. This study most likely would ask the participants very “basic” questions like “rank the wines” in the order you like them and try to identify what enclosure was used to “seal” which given glass of wine. There is a lot of research and studying going on, but the biggest obstacle is trying to figure out the most appropriate and accurate way of measuring oxygen transmission rate (OTR). In this study, instead of trying to give a “value” for OTR, they would look at one aspect of oxidation (“browning” of a white wine, and measure it through a clear glass wine bottle) and try to determine the rate of this “browning” under a given enclosure.

Salute

I beg to differ. It tells us what we need to know; what I need to know, at any rate; which is 'which closure will change the wine the least?' What else is important in packaging? If you used a scientific measure (such as consistency of free SO2 under a given closure), rather than tasting, as the criterion you would have the same result.

One would have thought this study would have been done years ago with so many screwcap bottles on the market today.

It has been, probably multiple times. A BC winery did this over 10 years ago.

One important aspect is missing and that is- What techniques are being used to produce the Sauvignon Blanc? Is it going to be fermented in stainless steel or barrel fermented? How is it going to be bulk aged prior to bottling? (The “bottle environment” should "complement" the wine making techniques and how the wine was handled prior to bottling).

Salute