August 2014 Issue of Wines & Vines

Using Closures to Customize Oxygen Transmission

Variety of alternative closures serves to protect and develop flavor characteristics

by Jane Firstenfeld
Four closure types
Innovations from purveyors of traditional cork (clockwise from top left), screwcaps, synthetic closures and technical corks offer winemakers more control of oxygen transmission rates.

Glass bottles remain the overwhelming favorite container for wine, despite the recent proliferation of alternative packaging. To accommodate winemakers who prefer glass, closure manufacturers have broadened their offerings to encourage flexibility in design while meeting increased demand for technical improvement.

As we’ve noted in previous reports, many major wineries now bring their bottled wines to market using diverse closures to match their various tiers, price points and varietals.

Eight years ago we covered a road show sponsored by the Cork Quality Association and APCOR, the Portuguese Cork Association, which presented scientific assessments of natural cork, synthetic stoppers and screwcaps and their ability to preserve wines for an appropriate time period. (See “Cork Suppliers Make A Compelling Case” in the August 2006 issue of Wines & Vines.)


  • With growing market success for alternative closures, winemakers and suppliers are focusing intently on oxygen transmission rates (OTRs), which can vary among closure types.
  • In general, synthetic stoppers and screwcap closures offer the smallest amount of OTR; manufacturers now offer different rates of oxygen ingress depending on winemakers' intentions.
  • Wineries are now more open to the option of using different types of closures to reflect price points, wine varietals and potential aging.

At that time, screwcaps had virtually taken over the New Zealand and Australian wine industries, and they were beginning to enter the mainstream in North America. Several presentations focused on the perception that screwcaps caused post-bottling “reduction,” unpleasant off- odors and flavors created by the mix of oxygen and sulfides.

Since then, manufacturers in each of these segments have labored to make their products more appealing for both age-worthy and drink-ready wines.

Recent research
During a June packaging conference at the University of California, Davis, Dr. Anita Oberholster, cooperative extension specialist in enology, reported on closure research performed by Dr. Andrew Waterhouse.

Natural corks have been used to seal wine bottles for around 300 years, she said. Their application introduced the concept of “aged wines,” because of cork’s oxygen permeability. “Oxygen ingress is highly variable” due to the varied properties of the natural closure, Oberholster explained.

She went on to describe the impact of oxygen transmission rates (OTR). “Wine aroma and color are influenced by oxygen exposure in the bottle and the formation of oxygen aroma compounds,” she said. Too much oxygen decreases fruity aromas and increases oxidative aromas.”

New Zealand’s signature varietal Sauvignon Blanc is one of the most sensitive, perhaps explaining the Kiwis’ early adoption of screwcaps. Red wines are less affected. Oxygen in the bottle eventually consumes SO2: 1mg of oxygen consumes 4mg of sulfur, the research revealed.

The Waterhouse team worked with winemakers at Napa’s PlumpJack Wine Estates, which had daringly introduced its 1997 super-premium Cabernet Sauvignon wines under screwcap.

“In the PlumpJack tests, natural cork showed the most variants in OTR outliers (extremes),” Oberholster said. Screwcaps and synthetic cork showed little difference over time. “The winemaker said the wine under screwcap tasted most like the wine she had bottled 15 months earlier.”

The UC Davis research also confirmed that incidences of cork taint (TCA contamination) had been reduced to 1%-2% due to production improvements, including potential analysis of every natural cork. However, “Natural cork is much more variable for OTR.”

Most types of closure are now available with varied oxygen transmission rates suitable for wines of different styles and price points. We contacted leading suppliers to learn what’s available now, and you may be surprised by the variety of options.

Natural cork
The oldest and most prestigious closure remains natural cork harvested from European cork forests.

“Technical” corks from the same sources present a similar look to the non-professional eye, with advantages in price—and potentially in protection from the “cork taint” that plagued the wine industry for decades. The cork industry has invested millions of dollars in research to protect wines from TCA.

“We have seen a dramatic increase in demand for cork of all types over the past four to five years, with our sales doubling in that timeframe,” said Vance Rose, director of sales and marketing at Amorim Cork, which manufactures natural and technical corks.

“Cork usage in the U.S. is growing significantly faster than the usage of alternative closures,” said Erica Wolfe of M.A. Silva USA, which produces cork closures made from natural cork materials, including 10 natural cork grades ranging from near visually perfect for ultra-premium wines through value-priced corks intended for high-volume labels.

“According to Nielsen Market Studies, the number of cases finished with cork has increased by 36% in the past four years, while alternative closures only grew by 6%. The median price for cork-finished wines is also 33% higher than the wines with alternative closures,” according to Wolfe. The price differential, it should be noted, may be a result of wineries’ choices to bottle higher-priced vintages under natural cork, due to lingering consumer perception that cork-finished wines are of higher quality.

On the other hand, “No oxygen enters a bottle through any form of natural cork from the outside,” Rose said. “All of the oxygen that does enter the bottle via a natural or technical cork is contained within the cork and is released slowly into the wine. We recommend natural corks (with a slightly higher, but finite, OTR) for red wines that might age and for higher-end white wines. We recommend technical corks for quick-selling, lighter reds and white wines with a retail under $10.”

“Research has shown that closures made from natural cork materials achieve that sweet spot of ideal wine development—neither causing reduction as many of the screwcaps can, nor causing premature oxidation as synthetics do,” Wolfe said.

Amorim cork closures “do not vary in price because of the OTR, but due to manufacturing costs,” Rose said. “We sell more technical corks simply because there is a greater volume of inexpensive wine sold. We sell to more than 1,200 wineries in North America—and certainly many of these use different cork closures for different wines in their portfolios.”

Wolfe agreed: “The price of our corks is not based on OTR. Our bestselling corks are natural corks. Wineries usually select their cork in correlation to the price point of their wine.

“Multiple manufacturers of alternative closures try to develop products that mimic the performance of cork, as natural cork has a proven record of protecting and aging wine. Natural cork stoppers can be used on wines intended for either immediate release or those intended for long-term cellaring,” Wolfe said.

Technical corks
Not just a hash of leftover cork scraps, technical corks are now carefully engineered to eliminate cork taint and other flaws. Many are also designed to provide different OTRs.

    Whatever happened to cork taint?


    A decade ago “cork taint,” derived from TCA (2,4,6- trichloroanisole), was perceived as the major issue with closures within the wine industry. Since then, diligent research and development by natural cork producers has minimized this wine flaw, and the cork industry has invested millions of dollars in research to protect wines from TCA.

    Research from the University of California, Davis, has confirmed that incidences of “cork taint” have been reduced to between 1% and 2% of all bottles due to production improvements including potential analysis of every natural cork. However, “Natural cork is much more variable for OTR,” according to enologist Dr. Anita Oberholster of UC Davis.

    To the non-professional eye, “technical” closures made from natural cork sources present a similar look to natural cork stoppers, while potentially offering advantages in price and more protection from “cork taint,” thanks to advanced production processes. There’s always room for improvement though—oxygen transmission rates have now risen to the forefront in terms of factors determining closure choices.


In addition to natural cork, M.A. Silva USA also produces “colmated corks, Silktop technical corks and Pearl micro-agglomerated corks,” according to Wolfe. Colmated corks consist of a solid natural cork body and a fine granular cork coating.

“Technical cork products, due to their greater density and slightly tighter fit within the bottle, could result in slightly lower levels of OTR,” she said.

M.A. Silva’s Silktop technical corks are designed primarily for mid-range wines that may benefit from short-term aging (three to four years), Wolfe explained. “Pearl micro-agglomerated corks are designed primarily for price-sensitive still wines and light sparkling wines.”

Amorim planned to introduce two new products this summer. Neutrocork Premium is a unit-molded micro-agglomerated cork “guaranteed to 1 part per trillion or less of TCA,” Rose said. Amorim’s Twin-Top EVO is a unit-molded micro-agglomerated body with natural disks on each end.

Diam Bouchage, a French company with a production facility in Spain, has conducted extensive research into the oxygen-permeability rates of its agglomerate closures. The company produces more than 1 billion corks annually; in North America they are distributed by G3 in Modesto, Calif.

To assess OTRs, Diam’s research team developed the permeameter. The machine consists of several round chambers of cylinders (similar to bottlenecks) that contain closures. These chambers connect two others—one filled with oxygen, and the other a vacuum that draws oxygen through the closure, measuring actual OTR.

Diam uses permeameter data for quality control, and for comparison with competing corks. Diam corks are available with varying OTR ranges: Diam 10 and 30, designed for wines made for long bottle aging, have the lowest rates, between 0.05 and 0.1 parts per million (ppm).

Other Diam closures provide OTRs between 0.15 and 0.35 ppm. The company tests about 350 closures daily for quality control. Francois Margot, Diam’s North American export manager, stressed that the exact amount of oxygen that enters wine depends on how the bottles are stored after packaging and during transportation.

Diam is now performing trials with universities in Italy, Spain and France to better understand how wines age under different closures. Margot said the goal is to pinpoint which rate of permeability works best for each varietal. The challenge, he said, is that no two wines are alike, and the same wine can react differently under different closures.

Synthetic stoppers have become mainstream in the past decade. During that time, Zebulon, N.C.-based Nomacorc has come to dominate the supplier side. “We now close nearly 15% of all still wines produced globally,” said Katie Myers, Nomacorc’s communications manager for the Americas.

“Nearly 60% of the top 500 wines sold in the U.S. are closed with a Nomacorc closure,” she said. Like other closure suppliers, Nomacorc has added to and improved its offerings. “Since the introduction of the Select Series in 2011, we’ve seen a big shift in wineries that use this for their premium wines,” Myers said.

Natural cork producers have appealed to many sustainable wineries, touting the environmental advantages of their products. Nomacorc’s response was to introduce its Select Bio Series, which utilizes plant-based materials—sugar cane biopolymers—to achieve a “zero carbon footprint closure.”

“Many wineries have begun trials” with the Select Bio closures, according to Myers, and Avalon Winery is using the closure for a portion of its 2012 California Cabernet Sauvignon.

Myers said that Nomacorc’s co-extrusion manufacturing process allows its closures to precisely control oxygen ingress rates. “From delicate white wines to robust reds, there is a Select closure suited for optimum post-bottling oxygen management. The average-priced wine closed under the Select series is $22, but can range as high as $100 per bottle,” she said.

Nomacorc provides its proprietary NomaSelector software, which guides winemakers through an analysis of their winemaking and storage to help choose the closure that best suits the each wine, Myers said. All closures are priced the same except for Select Bio, which carries a premium price due to its unique raw materials and supply.

“A winery looking to close a delicate, fruity white wine may use Select 100 to create an almost airtight seal to preserve aromas and flavors,” Myers said. “The same winery may use a Select 500 on a full-bodied, robust red wine that needs more oxygen to help speed up and soften the wine’s tannins,” she said.

During the past decade, as screwcapped wines have become a common sight at North American wine retailers, Stelvin has become almost as generic a brand name as Xerox, and the company remains a powerhouse. Amcor Flexibles of American Canyon, Calif., distributes the Stelvin closure line.

Jenna Riggs, Amcor Flexibles’ marketing coordinator, provided background about Stelvin’s success. “Historically there have only been two standard liners (that provide the OTR protection to screwcaps): Saranex and Saran Tin. Last year, Amcor launched a range of four new liners for Stelvin closures. These are composed of a variety of layers including aluminum, tin, ceramic, polyethylene and expanded polyethylene. These liners are also finished with a PET (polyethylene terephthalate) layer instead of PVDC (polyvinylidene chloride).

Amcor doesn’t designate these liners for particular varietals. “We seek to provide a range of options and let the winemakers choose their preferred OTR, depending on the level of oxygen and SO2 in the wine at bottling and the ideal duration they want to keep the wine in the bottle,” Riggs said.

Liner prices do not vary within Stelvin’s new Inside range, and they remain comparable to current liner options, Riggs said. Some 120 customers are conducting trials using the Inside range, and several have switched to the newer range.

Stelvin screwcaps first gained acceptance for crisp white and rosé wines. “Recently, we have seen an increasing amount of customers moving their Chardonnay, Pinot Noir and red blend wines to Stelvin, in a variety of price points,” Riggs reported.

She added that customized decoration—including head and skirt embossing—is drawing new customers to the screwcaps as well.

OTR results “in reality depend on the cooperation of neck finish sealing rim quality, sealing head setting and the impact of oxygen during the bottling/sealing process in general,” said Gisela Cartwright, COO of Mala Closure Systems USA. “We get tests made continuously by the independent institute Fraunhofer.”

Saranex remains the most used liner, Cartwright said, “not only because of its price advantages but also for its general suitability and advantages vs. cork and synthetic cork.” She added that Saranex’ “general suitability” includes freedom from cork taint “and leak-free storage of up to three to four years. It is reasonably priced and can be used for a variety of wines, if applied properly.”

Screwcap prices do vary due to differences in liners, Cartwright said. Mala’s LongCap VIN 30x60 DuR “enables nearly the same rate and even flow of oxygen transmission of Saranex in connection with flexibility for long-term horizontal storage, transportation, changes in temperature, internal pressure, compensation of faulty bottle finishes, and so on,” Cartwright said. There is no additional cost for these closures.

Relatively new to the competition is Napa’s VinPerfect, purveyor of the SmartCap screwcap. VinPerfect founder and CEO Tim Keller described the product: “We start with the most reliable closure system available, the 30 x 60 ROPP (roll-on pilfer-proof) screwcap, then add our patent-pending liner, which admits nano-scale quantities of oxygen.

“These very small amounts of oxygen help enhance and enrich the wine in the bottle. The highly engineered liner vastly improves the consistency of the screwcap closure compared to other, more inconsistent liners,” Keller said.

Three different OTRs are available: light, 0.08mg oxygen per year; medium, 0.16mg; and medium plus, 0.37mg. These are achieved via a patent-pending, oxygen-regulating liner consisting of pharmaceutical-grade, high-density elastomer for consistent sealing and compression-set resistance; upper polyester (PET) layer for initial oxygen regulation; vapor-deposited aluminum coating to fine-tune OTR; a lower PET layer to encapsulate aluminum and provide a food-grade contact surface. Heavy-gauge films throughout the liner eliminate wrinkling during application to improve the seal’s consistency.

All the closures are priced the same, Keller said, and they are suitable for the entire range of wine price points. “Wineries definitely use our light, medium and medium plus SmartCaps on different varietals,” he said. In general, however, light is applied to Sauvignon Blanc, Riesling, Pinot Gris/Grigio and rosé, while medium works for Chardonnay, Viognier, Pinot Noir and Merlot, and medium plus is well suited to Cabernet Sauvignon, Syrah, Sangiovese, Zinfandel and Bordeaux-style blends.

Keller summed up two related trends: “The first is that more wineries are adding screwcaps to their mix of closures.” They start with a white varietal or rosé, expanding to more varietals and/or high-end labels, he observed.

Second, “Almost every winery we talk to that doesn’t already use screwcap is actively switching at least some of their production to screwcap,” he said. “As VinPerfect shifts the value proposition to include post-bottling oxygen management, we expect more of those fence-sitters to make that shift.”

How to decide
In the end, closure decisions are nearly as complex as the winemaking process, and OTR is only one aspect of the final equation. The image and desired market for each wine must be considered along with sustainability issues, price points, potential aging and consumer acceptance.

Winemakers should consider how their wines will taste when they are, sooner or later, opened by a consumer. Reputable suppliers will provide data to help walk you through the decision-making process. And don’t be surprised if you decide on different closures for different wines, and change the plan along the way.

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