5/17/2017
UC DAVIS VITICULTURE AND ENOLOGY
CORK TAINTS
ANITA OBERHOLSTER
MAY 18, 2017
Wine Flavor 101C: Recognizing Non-Microbial Taints
UC DAVIS VITICULTURE AND ENOLOGY
Introduction: Cork Taints • Characteristics of cork taints • Fungal, earthy, moldy, corky, mushroom or straight musty • What causes cork taints? • Haloanisoles (TCA, TCB) • Alkylmethoxypyrazine (MDMP)
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Cork Taint • Cork taint caused by aroma intense compounds in the cork transferring to the wine • Economic loss, estimates 1-5% of bottles effected • Main contributor is
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Cork Taint • TCA is responsible for 80-85% of cork taint • Many times the only compound analysed • Aroma threshold 1.4-4.6 ng/L
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TCA • TCA taints sometimes from other sources than corks • Contaminated processing aids • Oak barrels • Wineries with high background of these compounds • Bottels • Bottle to bottle variation indicate cork taint
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Other Chloroanisoles • Frequently detected with TCA: • 2,4-dichloroanisole (2,4-DCA) • 2,6-dichloroanisole (2,6-DCA) • 2,3,4,6-tetrachloroanisole (TeCA) • Pentachloroanisole (PCA) • TCA always most important contributor
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Origin of Chloroanisoles in cork
• Already present in bark of living cork trees • 2,4,6-trichlorophenols (TCP) produced from naturally-occurring phenols and chlorine from sanitizers, cleaning products and town water • Chlorine-bleaching treatments of cork, now discontinued • Chlorophenol biocides accumulated in environment • Microorganisms capable of methylation are present in cork, form TCA from TCP
Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226‐240. Simpson and Sefton Austr J Grape Wine Res 2007 13 106‐116
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Origin of Chloroanisoles in cork • Decline of TCA in corks • Suggest depletion of source of contamination
Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226‐240. Simpson and Sefton Austr J Grape Wine Res 2007 13 106‐116
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Transmission from Cork to Wine • Transmission depend on several factors: • Solubility of taint compound in wine • Affinity of taint compound for cork surface and interior • Location of taint compound on cork • Rates of taint compound migration through cork • Volume of wine in contact with closure • Only TCA have been studied in detail • All discussion - according to TCA findings
Sefton and Simpson Austr J Grape Wine Res 2005 11 226-240
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Transmission from Cork to Wine • TCA – high affinity for cork • Corks soaked in contaminated wine will absorb TCA • Only small amount of TCA in cork extracted into wine • TCA can contaminate outside of cork closures, but does not migrate through cork • Contamination only from part of cork in contact or close proximity to wine
Capone et al., Austr. J. Grape Wine Res. 2002, 8, 196-199. Sefton and Simpson Austr J Grape Wine Res 2005 11 226 240
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Transmission from Cork to Wine • Formation of TCA in situ have been suggested • Experiments show no conversion of TCP to TCA in bottle (Liacopoulos et al., 1999)
Capone et al., Austr. J. Grape Wine Res. 2002, 8, 196-199. Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240
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Screening for Chloroanisoles
• Screening method usually based on sensory assessments of wine soaks or corks in damp environment • Advantage – low cost, detect both known an unknown taints • Disadvantage – variation in performance of assessors • Low sensitivity and corks soaked in batches • Soaked few hrs to 2 days in mostly aqueous alcohol
. Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240
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Screening for Chloroanisoles
• Instrumental analysis of TCA • Identify specific taints as well as precursors
SPME-GCMS
. Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240
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Screening for Chloroanisoles • No screening method reflects accurately level of taint in bottle • Whole surface of cork is extracted in cork soaks • Short soaking periods means only ‘rapidly released’ TCA measured • Batches soaked, if one cork contaminated the average could be below detection limit • However, these measurements still help predict bottle taint
. Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240
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Screening for Chloroanisoles • TCA contaminated corks detected (1%), much lower than incidence of cork taint observed (5%) – Australia, 2005 • Underestimation during cork assessment • Short duration of extraction (24-48 hrs) • Presence of usually 5 corks per soak and small vol of wine • Despite limitation of methods, badly contaminated corks will be detected
. Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240
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Removal of Chloroanisoles • TCA diminished by aeration • Accelerated by high moisture content and heat • Steam-cleaning removes 75-80% of rapidly releasable TCA • Bottle trials show good results • Supercritical carbon dioxide extraction • AWRI found no TCA transfer to wine after 2 years using these closures
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Removal of Chloroanisoles • Other techniques designed to diminish TCA in corks • Microwave treatment • Enzymes • Use of physical barriers • Removing TCA from wine • Can’t be filtered or RO removed • TCA absorb on to certain materials • Polyethylene, • Aluminosilicate sheets
.Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240 Vlachos et al, European Food Research and Technology; 2007. 225(5/6):653-663
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Tribromoanisole (TBA) • 2,4,6-Tribromoanisole (TBA) identified in tainted wine • ‘Musty or corked’ character • Detection threshold of 4 ng/L • Produced by microbial breakdown (O- methylation) of precursor 2,4,6- tribromophenol (TBP)
Chatonnet et al., J. Agric. Food Chem. 2004, 52, 1255-1262
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Sources of TBA • Similar to TCA, plastic material in general readily absorb TBA and to lesser extent TBP • Polyethylene- or polyester-based winemaking equipment, silicon bungs etc. contaminated
Chatonnet et al., J. Agric. Food Chem. 2004, 52, 1255-1262
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Sources of TBA • Wineries with TBA problems • Wooden timbers massively impregnated with TBP • Some paints also contained TBP • TBP used as flame retardant or/and fungicide
Chatonnet et al., J. Agric. Food Chem. 2004, 52, 1255-1262
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In summary TCA/TBA • Both TCA and TBA have low detection threshold • Distinctive ‘musty and/or corky’ character • Screening methods useful in prediction of bottle taint although not absolute • Effective methods available to remove contaminants from cork • Incidence decreasing as sources of contamination depletes • Treatments available to decrease cork taint in wine
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Cork Taint: Alkylmethoxypyrazines • ‘Wet cork’ or ‘corky’ character, ‘fresh hazelnut’ or ‘herbaceous’ character and ‘moldy’ or ‘earthy’ character at high concentrations • Detection threshold of 2.1 ng/L • Measured in affected wines, 1.4 – 3.5 ng/L
Chatonnet et al., J. Agric. Food Chem. 2010, 58, 12481‐12490. Simpson et al Agric Food Chem 2004 52 5425‐5430
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Formation of MDMP • Several microorganisms able to synthesize MDMP • Serratia odorifera , C. crocatus, and R. excellensis • Biosynthesize from amino acids not well- known • The alanine amide condenses with methylglyoxal (pyruvaldehyde) to form 2-hydroxy-3,5—DMP, which after methylation produces MDMP • L-alanine and L-leucine responsible for highest conc of MDMP • Lesser extent L-valine and phenylalanine
Chatonnet et al., J. Agric. Food Chem. 2010, 58, 12481‐12490.
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Sources of Contamination: Corks • Cutting punches used for cork cylinders possible source of taint • Opposite to TCA, it has low affinity for corks and easily extracts into wine • High contamination levels, 86% corks tested > 2ng/L • Corks < 5 ng/L, (34.9 %) minimal risk • Batches with 5.1-15.0 ng/L, medium risk (51.2 %) • Batches with > 15.1 ng/L , extreme risk (16.3%)
Chatonnet et al., J. Agric. Food Chem. 2010, 58, 12481‐12490.
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Sources of Contamination: Oak • Found wine contaminated with MDMP, in vats with oak chips, none found in same wine without oak chips • Wood used for industrial wood chips stored on ground, possible source of MDMP • Microorganisms found in soil that produce MDMP • MDMP destroyed by heat, 220゜C remove 93% • Untoasted and lightly toasted oak may contain MDMP • Heat at 105゜C for 10 min only removes 50% of MDMP
Chatonnet et al., J. Agric. Food Chem. 2010, 58, 12481‐12490.
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In Summary MDMP • R. excellensis microorganism primarily responsible for MDMP in cork • Both cork and oak are sources of contamination • Decontamination techniques • Similar to TCA removal • Lower affinity for cork, higher removal • MDMP > 10 ng/L in 40% of corks • Systematic monitoring needed similar to TCA • Origin of microorganism • Likely storage of raw material near soil
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