These wines bottled with natural corks showed a larger disparity in color due to cork’s wider range of oxygen transmission. Source: UC Davis

Napa, Calif.—The recent Wines & Vines Packaging Conference featured two tastings that showed how closure choice can affect wine quality.

The first tasting, sponsored by Guala Closures, took place in the morning and featured wines by CADE Winery in Napa Valley. CADE is part of the PlumpJack Group, and John Conover, general manager of PumpJack Winery and partner in CADE, said the company had been open to alternative closures because the founding partners saw first-hand how unpleasant a corked wine was for customers of the original PlumpJack Wine & Spirits shop in San Francisco, Calif. He said that experience helped motivate the company’s willingness to bottle its estate wines under screwcap as well as participate in a study on closures with the University of California, Davis.

Both sessions, held in the demonstration kitchen of the former Copia building in Napa, Calif., drew a full crowd of 75 people. The tastings were conducted with Rastal glassware from Germany, provided by conference sponsor Chrislan Ceramics.

Dr. Anita Oberholster, cooperative extension specialist in enology for UC Davis, provided an overview of the research project that is being headed up by Dr. Andrew Waterhouse as well as some early conclusions. “The first question the research is attempting to answer is whether variability using a specific closure is large enough that a consumer can taste the difference,” Oberholster said.

Collaborative closure study

PlumpJack and UC Davis arranged to have 200 bottles of the 2011 CADE Sauvignon Blanc bottled with an Amorim natural cork, Nomacorc Select 300 synthetic cork or Amcor Saranex screwcap, for a total of 600 bottles in the study. The rate of oxidation was observed through color darkening (or color absorbance) over time as measured by a spectrophotometer, with each bottle acting as its own control. Using each bottle as a data point, the researchers were able to create a slope based on the observed OTR.

Based on the study, screwcaps appear to offer the most consistent OTR, followed by synthetic corks. The greatest variation came from natural corks. Oberholster said getting a better understanding of closure variability should help winemakers make informed decisions at bottling to ensure wines conform to a specific style.

While the screwcap and synthetic closures did a better job of preserving the wine as it tasted at bottling, natural corks added “more aging character,” which resulted in a more complex wine. Depending on the wine or winemaker, this aged character could be a desirable trait.

“At the end it is also about helping the winemaker to make informed decisions based on objective data,” Oberholster said. “We are currently planning the sensory testing, so the answer to the key question has yet to be answered.”

Preserving versus aging

The PlumpJack team including CADE winemaker Danielle Cyrot brought bottles of the Sauvignon Blanc that is part of the UC Davis study as well as its 2008 CADE Howell Mountain Cabernet Sauvignon, which was bottled under screwcap and natural cork. The tasting was conducted blind, and Cyrot gauged the opinion of those in the audience. The greatest variation in taste came between the synthetic corks and screwcap versus the natural cork, which almost tasted like a different wine.

Cyrot described the Sauvignon Blanc bottled with natural cork as exhibiting more pear, melon, honey and cantaloupe with less acidity and being a bit more rounded, softer and showing more of the oak. The synthetic cork and screwcap wines were both “fresh, flinty, floral” in Cyrot’s opinion, but had slightly different fruit flavors. “Basically, I thought the synthetic and screwcap closures performed best at preserving some of the aromas and flavors I was trying to capture in the bottle,” she said. “They both tasted more like the day the wine was bottled.”

The cork-sealed wine tasted the most different to Cyrot, and this appeared to be the consensus of those in the audience as well. “The cork closure stood out as most different, but not necessarily in a bad way,” she said. “It was just more aged.… I felt the closure had played a role in stylistically changing the wine.”

The Cabernet Sauvignons tasted relatively similar, and when Cyrot asked the audience to raise their hands to indicate preference, the room was about evenly split between the two.

Cyrot said she still needs more time to understand what type of closure is best for CADE’s reds. “I am making sure that the tannin structure and mouthfeel are balanced before putting the wine in bottle. The wine still tastes like Howell Mountain, but hopefully the tannin structure isn’t a grippy, hard, undrinkable kind of tannin,” she said. “So I want a closure that will preserve the fruit aromatics without overly oxidizing the wine.”

Screwcap options

Later in the day, Doug Fletcher the vice president of winemaking for the Terlato Wine Group, presented wines from his own trial on different screwcaps. The tasting was sponsored by Mala Closures and featured a 2012 Pinot Grigio bottled in February 2013 under five VinPerfect closures with different oxygen transmission rates, a Saranex lined closure and one with Saran-tin.

The bottles with the lowest OTRs had some sensory attributes of reduction as well as a lean texture. On the other end of the oxygen-transmission spectrum, the wines were rounder and more fully developed. Fletcher’s preference, which was also the preference of those in the audience, was for the wines bottled with a closure offering a mid-range OTR.

He said he used a screwcap with a Saranex liner for the trial wine's commercial release because at the time he knew it resulted in less reduction issues than the Saran-tin liner. He later opted to use the VinPerfect liners because they provided a more consistent OTR, and wines sealed with the VinPerfect Medium were among those preferred by the audience at the tasting session. Fletcher said the trial was to see what OTR level works for each wine and he said he’s still not sure what the answer is. While he thought wines bottled under closures with higher rate OTRs would have browned or gone oxidative, Fletcher said they have held up quite well. In light of what he’s learning through the study, Fletcher said he thinks less sulfur dioxide could be used in the cellar in tandem with a nitrogen-drip system on the bottling line. He said he also has more confidence in the stability of wines with higher OTR closures—at least for the short term.