13:01 | 15.03.2010
Silver Oak Cellars and Cork Supply USA Pioneer Use of Technique to Detect TCA in Large Format Corks
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 breakthrough
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 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.
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