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28 W i n e s & V i n e s A U G U s T 2 0 1 4 cork's oxygen permeability. "Oxygen in- gress is highly variable" due to the varied properties of the natural closure, Ober- holster 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 Sau- vignon Blanc is one of the most sensi- tive, perhaps explaining the Kiwis' early adoption of screwcaps. Red wines are less affected. Oxygen in the bottle eventually consumes SO 2 : 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 con- tamination) had been reduced to 1%-2% due to production improvements, includ- ing 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 suppli- ers 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 Eu- ropean 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 in- dustry 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, di- rector of sales and marketing at Amorim Cork, which manufactures natural and technical corks. "Cork usage in the U.S. is growing sig- nificantly faster than the usage of alterna- tive closures," said Erica Wolfe of M.A. Silva USA, which produces cork closures made from natural cork materials, includ- ing 10 natural cork grades ranging from near visually perfect for ultra-premium wines through value-priced corks in- tended 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," ac- cording to Wolfe. The price differential, it should be noted, may be a result of winer- ies' choices to bottle higher-priced vin- tages 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 recom- mend 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 dif- ferent 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 alterna- tive 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 engi- neered to eliminate cork taint and other flaws. Many are also designed to provide different OTRs. In addition to natural cork, M.A. Silva Avalon 2012 Cabernet Sauvignon emerges from the corker sealed with Select Bio closures. View Video: Members of the Plumpjack Group's winemaking team discuss why the company decided to transition to screwcap closures and describe their ongoing research into the issue in this video produced by Cade Estate Winery. C L O S U R E S