This Membrane Can Add Consistency To Wine Quality

Can an ‘inert, semi-crystalline, oxygen-selected membrane, heat-welded to the end of cork’ improve consistency in wine quality? Several winemakers—including at least one with a Top Ten listing in Wine Spectator, and 100-point scorings from wine critic Robert Parker—believe so.

The evolution of this technology was not—as its inventor Dr. Gregor Christie said, ‘something that just pops into your head.’ Instead, it was born unexpectedly at the crossroads of two disciplines.

ProCork is a cork with an extremely thin, clear membrane placed over both ends—hardly detectable to the human eye. It allows oxygen to pass through at a consistent rate—but blocks passage of contaminants that include the chemical compound TCA—or 2,4,6-trichloroanisole—which causes a foul and gluey ‘corkage’ taste in infected wines.

Evolution Of Invention

After working as a chemist with British Petroleum in Australia, Gregor Christie obtained his doctorate in chemical engineering at the University of Melbourne. He next toiled in a material science laboratory in the same city as director of research for food and packaging.

Eventually, he was tasked with a unique opportunity.

Earlier this century (and last century) many corks were plagued with problems of TCA contamination. This occurs when lignin associated with cork breaks down to form phenolic compounds. If these chemically combine with chlorine—either from fungi living on cork bark, or found within the surrounding environment—the resulting TCA provides an odor and taste so strong that humans detect it at levels of about five parts per trillion. That’s the equivalent dilution of about one single raindrop (considering a raindrop diameter somewhat less than 3 millimeters, or 0.11 of an inch) within an Olympic size swimming pool.

The cork industry aggressively tackled and reduced this TCA problem during the past two decades. Portuguese cork companies banded together and adopted far more rigorous hygiene and quality control practices.

However, at the time that this TCA situation was still annoyingly problematic, Dr. Christie’s then employer—the Commonwealth Industrial Research Scientific Organization—was asked to recommend alternatives to cork for closing wine.

Dr. Christie and a team sealed a series of bottles (with the same type of wine inside) with multiple types of closures, including screwcap, synthetic cork, agglomerated cork and even a closure derived from wool. After waiting eighteen months for wine to age, they opened these bottles. A panel of professional tasters then sampled each. It turned out that the best, as well as worst, closure appeared to be cork. The problem with cork was primarily not one of TCA contamination as much as oxidation—allowing excess air to contact wine and reduce its vibrancy and life.

Dr. Christie and I recently spoke. He explained the scenario.

“All wines were professionally tasted. The best closure was cork. The fruit was brighter, the wine cleaner, more delicate. Every other closure after that was just a bit more dull. And the worst closure was also cork. There was a range of wines with varying degrees of oxidation. It was not a TCA issue.

“Two things I pulled out of this experience were—first, that there’s an optimum amount of oxygen that wine wants. Second, cork has a big range of OTR—oxygen transfer rate, or permeability. The variability is just inherent in the cork material.”

During a career immersed with material properties, Dr. Christie had worked at extremely small scales. These included utilizing ‘synthetic crystals with molecular sieve properties’ and manipulating ‘selective permeabilities.’ To better understand—consider shrinking a kitchen strainer down to a microscopic size, then gaining intimate familiarity with how it operates when made from different materials.

Dr. Christie realized that his position was unique.

“There I was—on one hand I had all this information about selective permeabilities and membranes and how to make them, and on the other hand learning about a product with a range of variabilities in permeability—cork. It was just a really obvious combination to put the two together. It would not be obvious to someone just working with polymers, or to someone just working with cork.”

During the following years he focused on a project during free hours.

“It was basically done at home with an ironing board and an iron. Just looking at various plastics and polymers. I worked out what layers needed to be at what position, and had them manufactured. Five layers. I went to a company that laminates polymers and got that done on a small run. From there I just started approaching people. Someone crossed my path who was a bit of a salesman and was into startup companies. We ended up with a company based in Melbourne.”

ProCork launched in 2001. Its first commercial release was in 2003. 

During the next decade and a half, this small company produced and sold more than 300 million membrane topped corks. Clients included the Foster’s Group (which produces not only well known beer, but also wine).

How The Technology Works

Corks ends are covered with a five-layer thick membrane (both ends—because of uncertainty as to which end will go into a bottle). This total membrane thickness is 50 microns (0.05 millimeters)—or about three quarters the width of a human hair. This membrane achieves two goals. First, it ensure the rate of oxygen transfer between outside and inside a bottle remains similar for all corks. This results in less taste variability between different bottles of the same wine from the same company. Second, because pores are large enough for oxygen molecules to pass through, but too small to allow passage of TCA and other contaminants, these membranes effectively screen out and block significant impurities from entering wine.

That second effect, however, is best avoided. Dr. Christie explained.

“The TCA issue is kind of secondary. We do stop it passing through the cork, but in general you don’t want a cork with TCA. You want to be rid of it. So quality assurance procedures and disinfection and hygiene can reduce its incidence. But the bigger problem with corks is always variable permeability.”

According to a 2004 study by the Australian Wine Research Institute, a panel of 10 ‘wine sensory evaluation’ judges with ‘extensive experience’ blind tasted 15 temperature-controlled wines using 14 different types of enclosures over a two-day period. These samples were poured in constant volume glasses within isolated and ventilated tasting booths. These panelists then scored several aroma as well as taste (or ‘palate’) attributes associated with wines, such as ‘floral,’ ‘citrus,’ ‘honey,’ ‘herbaceous’ and ‘oxidized.’ Scores were on a scale from 0 to 9, with 1 corresponding to detectable, 5 corresponding to a moderate intensity and 9 to strong intensity. Wines under ProCork membrane closure were, overall, ‘rated highest amongst the perceived fruit levels’ (with a mean score of 5.1 for aroma and 5.4 for flavor, or ‘palate’).

The Present And Future

ProCork recently acquired a new funder and partner with Richard Serisier, an Australian entrepreneur with family roots in Bordeaux (he recently sold a sizable château he renovated in Bordeaux to a Chinese investor). Serisier has now invested in a cork farm and production unit in Portugal.

Wineries now using Pro-Cork include Peter Michael Winery of Napa Valley in California, Jeff Runquist Wines in Amador County, California and Bass Phillip of Victoria, Australia.

In 2019 ProCork patented a device to measure oxygen transfer out of bottles. It shows rates of oxygen leaving a bottle as being four to five times faster for regular corks than for ProCork. When this air was tested using a ‘gas chromatograph’ analysis—which basically graphs the chemical signature of a chunk of air—it sometimes ‘spiked high’ on bottles not sealed with ProCork, indicating an inflow of oxygen into wine that may be too high for optimal aging.

Dr. Christie explained.

“It’s indicating that oxygenation is coming on too quick, and the wine isn’t able to incorporate it in a usual way. You get a 30-year-old Bordeaux wine and it clearly has the effects of air over that 30 years. But it’s gentle; it makes the wine better. But if it comes on too quick you get obnoxious things such as acetic acid and aldehydes that are not on a pleasant profile.”

Working with Serisier in Portugal as well as traveling from Australia to the U.S. and Europe constantly, Dr. Christie realizes how dramatically his life has changed from days of toiling in a materials laboratory.

“I really like the wine industry. I fundamentally thought going to a plastic cork was the wrong way. Wine is more of a natural product, more hand crafted—not industrial. I’d always thought the solution was probably better off being with cork rather than with some other industrial process.

“This work is really satisfying. It’s clear when you pick up a bottle. Like those 2009 bottles there where companies bought and used ProCork? Taste it, and you’ll see the benefit.”