Purdue Extension FS-55-W Commercial Winemaking Production Series Cork Quality Control Winemakers should check carefully for tainted corks

By Christian Butzke The rate of cork taint — the musty, much to the dismay of winemakers and moldy off-odor in wine, stemming by consumers alike. So if your winery Enology Professor and large from the growing, processing continues to have problems with tainted Department of Food Science and shipping of natural bark corks — closures, below are the proper sampling Purdue University has been significantly reduced in recent procedures to keep the taint rate below years. This significant development 1.5 percent. This translates into one out [email protected] within the wine industry is due to of 67 bottles, an occurrence that — even pressure from winemakers and for a “super core” consumer who drinks subsequent improvements in the wine at least several times a week— will production process and quality control at be rare enough to be arguably cork manufacturers, distributors, and acceptable. associated wine laboratories. In the mid-1990s, the taint rate was estimated Sampling protocol between 3 percent and 5 percent of Simply put, if one wanted to assure that bottles, about one in every other case. only one in 67 corks is bad, one would As a consequence, by 2009, at Purdue’s have to sample at least one out of 67 Indy International Wine Competition, corks. In larger lot sizes, the actual the use of bark corks as bottle closures sampling size increases slightly to had dropped to less than two thirds of all decrease the statistical probability of 3,000+ entries, as winemakers switched accepting a large lot of tainted corks. to synthetic corks and screw caps. The For each 5,000-cork bale and when using problem of TCA (2,4,6 trichloroanisole), the simplest fixed-sample-size plan the main impact component for cork applicable to wine closures (ANSI/ASQC taint, has not completely disappeared, Z 1.4-1993 sampling plan for normal

A wine bark cork after 30 years in a bottle

The information in this publication is based on material from Winemaking Problems Solved, edited by Christian Butzke, Woodhead Publishing Ltd. inspection, general inspection level I; supplier with bottle. Any sampling shortcuts, however, are a good track record), the winemaker has to sample, complete waste of the enologist’s time. If the winery soak, and sniff 80 corks. If four or more of those 80 lab does not have the time or resources to conduct a corks were tainted, the lot should be rejected and full sampling and sensory evaluation test, then the sent back to the supplier. burden must be passed on to the manufacturer or Corks are a natural and renewable product from the distributor of the closure. Both trust and verification bark of the cork oak tree. Therefore, the sampling of are essential to a lasting relationship between such a naturally variable part of wine packaging winemaker and closure manufacturer. The perfect cannot be compared to, e.g., ammunition, which is closure is what makes wine different from all other mass-produced by precision machinery. Using beverages, complements its special value-added reduced sampling protocols — such as the old military image, and remains a conversation topic in itself specs MIL-STD-105E, which may be applicable to M16 among educated consumers. However, it should never bullets — will not work for wine corks. compromise the great work that the winegrower and winemaker have created. Cork soaking Medium: Tasting room staff training Finally, it is crucial that the tasting room staff is • Dilute 40 percent alcohol (80 proof) generic vodka trained to recognize TCA immediately when a new to10 percent alcohol by volume with distilled bottle is opened, as it could affect up to 25 potential water (1 part vodka plus 3 parts water). customers who taste their 30 mL sample of a tainted Procedure: wine. An appropriate training protocol can found in • Place ONE cork in a 50 mL disposable centrifuge the publication below, which also includes detailed tube. sampling options: • Fill with vodka-water mix; close. Cork Sensory Quality Control Manual • Soak for 24 hours at room temperature. C. Butzke and A. Suprenant University of California ANR Publication Number: • Smell opened tube for musty, moldy TCA off-odor. 21571 • Discard tube, cork, and testing solution. ISBN-13: 978-1-60107-343-3, Copyright Date: 1998 Advanced sampling protocols http://books.google.com/books?id=uTQEEAWTKFk C&printsec=frontcover More flexible but slightly more involved quality control plans include the recommended Fraction Defective Sampling Plan, and the Sequential Probability Ratio Test. All three plans are valid as long Reviewed by: Richard Linton as the protocols are applied correctly. None of the Professor of Food Science and above plans can circumvent the principles of applied Director of the Center for Food Safety Engineering statistics. Department of Food Science, Purdue University Bruce Bordelon Outsourcing Viticulture Professor Few winemakers are likely to have the time to sample Department of Horticulture & Landscape Architecture, Purdue University and test 80 corks for each 400 cases of wine they

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