Silver Oak Cellars, working with Carlos Macku, Lesa Gonzalez, Ana Cristina Mesquita and Leonard C. Kirch at Cork Supply USA and Cork Supply Portugal, has pioneered the commercial use of a new sensory evaluation method for detecting the presence of TCA (2,4,6-trichloroanisol), the chemical compound responsible for cork taint, in corks for large format wine bottles.
Called “dry cork sensory screening,” the method assures that virtually all of the tested corks are free of TCA and any other sensory defects. Presented by Silver Oak Cellars’ Christiane Schleussner to her peers at the annual American Society for Enology and Viticulture in June, 2009, the procedure is outlined in an article recently published in the Journal of Agricultural and Food Chemistry, Vol. 57, Issue 17. Link: http://pubs.acs.org/doi/abs/10.1021/jf901135p?prevSearch=cork%2Bsoak&searchHistoryKey
“We’ve always had an extensive collection of library Silver Oak wines. Not only is it a tangible record of our history, but we’ve found that many customers love having access to older vintages, particularly in large format bottles”
“We wanted to develop a method that would virtually eliminate instances of ‘corked’ big bottles,” said Schleussner. “Once we proved its efficacy, we decided to share it with the industry.”
Silver Oak and its sister winery Twomey Cellars already have one of the strictest cork quality control protocols in the wine industry. By randomly blind testing hundreds of corks from dozens of lots, tracking lots with a number/letter sequence and retesting cork lots using both individual and group cork soaks, the wineries have significantly reduced instances of TCA in their 750ml bottles. For large format bottles, however, they wanted to see if the rate could be reduced to zero.
Working with researchers at Cork Supply USA and Cork Supply Portugal, Schleussner developed a non-destructive “dry soak” method where each and every large format cork was held individually in a sealed glass jar containing 5-10 drops of de-mineralized water. The moist environment volatizes the molecules during a 48 hour period and then the corks are “sniffed” by an expert panel. Out of 2,296 corks, 138 specimens (6% of the total population) were rejected due to unusual odors ranging from mild to severe. The rejected corks were then chemically analyzed for TCA, and over 40 were identified as having extremely low TCA levels of 1.0 ppt (parts per trillion) or more.
“This method is very labor intensive; the process takes a strong commitment,” says Schleussner, who notes that because of fatigue, the team can only sniff 200 corks in one sitting (with a break every 50 corks). “But dry soak screening is a clean, non-destructive method that ensures that the wine in our large-format bottles is protected. We know our customers are getting what they expect.”
In a related project, Silver Oak Cellars recently recorked its entire large format library starting with the 1993 vintage and working back to the 1970s. The winemaking team uncorked each wine, sampled and discarded wines with off aromas and flavors, topped off each sound bottle with wine from the same vintage, recorked them using a “dry-soak” tested cork, and refoiled, cleaned and returned each bottle to its case or wooden box. In all, over 2,500 bottles were examined and recorked, including magnums, three-, five-, six-, twelve- and even eighteen-liters of Silver Oak Napa Valley, Alexander Valley, and Bonny’s Vineyard Cabernet Sauvignon.
“We’ve always had an extensive collection of library Silver Oak wines. Not only is it a tangible record of our history, but we’ve found that many customers love having access to older vintages, particularly in large format bottles,” says Daniel Baron, Director of Winemaking. “With our dry-soak method, we can guarantee our customers a pristine bottle of large format library wine.” The wines are available for sale through Silver Oak’s tasting room.
Silver Oak Cellars, founded in 1972 and Twomey Cellars, established in 1999, are owned by the Duncan family. With a focused dedication to winemaking, the family operates four wineries that produce four varietals. Silver Oak produces Napa Valley Cabernet Sauvignon at its winery in Oakville and Alexander Valley Cabernet at its Geyserville facility. Twomey Cellars in Healdsburg produces Pinot Noir and Sauvignon Blanc; Twomey Cellars in Calistoga focuses on Merlot.
SOURCE: Silver Oak Cellars