Musty Taints
Anita Oberholster
Introduction: Musty Taints
• What off-odours are classified as musty
taints?
– Fungal, earthy, moldy, corky, mushroom or
straight musty
• What causes musty taints?
– Haloanisoles (TCA, TCB)
– Alkylmethoxypyrazine (MDMP)
– Carbon unsaturated aliphatic compounds
with carbonyl function (1-octen-3-one, 1nonen-3-one)
– (-)-Geosmin
Musty Taint: 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
2,4,6-trichloroanisole (TCA)
• Responsible for 80-85% of cork taint
• Many times only compound analysed
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
Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240.
TCA
• ‘Musty’, ‘mouldy’, ‘wet cardboard’ character
• Generally detection threshold given as 1.4-4.6
ng/L
• Threshold varies substantially among individuals
– 1 –250 ng/L (white wine) experienced panellists,
group threshold 17 ng/L
– 2.5 –250 000 ng/L (white wine) inexperienced
panellists, group threshold 210 ng/L
– 1-2 ng/L experienced judges
• TCA chemically stable, will not degrade over
time
Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240.
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
2,4-DCA
2,6-DCA
TeCA
PCA
Origin of Chloroanisoles
• Origin of chloroanisoles in cork
– Already present in bark of living cork trees
• 2,4,6-trichlorophenols (TCP) produced from naturallyoccuring phenols and chlorine from sanitizers, cleaning
products and town water
• Chlorine-bleaching treatments of cork, now mostly
discontinued
• Chlorophenol biocides accumulated in environment
• Microorganisms capable of methylation are present in cork,
form TCA from TCP
– 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.
Origin of Chloroanisoles
• Co-occurence of TCA with other chlorinecompounds
– If co-contaminants contain fewer chlorine-atoms –
indicate sources as town water, sanitizers or
bleaching agents
– If co-contaminants contain higher number of
chlorine-atoms indicate PCP or TeCP-based biocides
– Presence of both indicate multiple TCA-producing
pathways
Simpson and Sefton, Austr. J. Grape Wine Res. 2007, 13, 106-116.
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.
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
• 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.
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
• Instrumental analysis of TCA
– Identify specific taints as well precursors
Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240.
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.
Screening for Chloroanisoles
• TCA contaminated corks detected (1%), much
lower than incidence of cork taint observed (5%)
– 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.
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
• Other techniques designed to diminish TCA
– Microwave treatment
– Enzymes
– Use of physical barriers
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 (Omethylation) of precursor 2,4,6-tribromophenol
(TBP)
TBA
Chatonnet et al., J. Agric. Food Chem. 2004, 52, 1255-1262.
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
• 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.
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
Musty Taints:
Alkylmethoxypyrazines
2-Methoxy-3,5-dimethyl-pyrazine (MDMP)
• ‘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.
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-alaine 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.
Source 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.
Simpson et al., J. Agric. Food Chem. 2004, 52, 5425-5430.
Source 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.
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
Other Musty Taint Compounds
• Three compounds detected in cork taint wines
other than haloanisoles or MDMP
– Geosmin (‘earthy’ character)
• Detection threshold 25 ng/L
– 2-Methylisoborneol (‘earthy/musty’
character)
• Detection threshold 30 ng/L
– 1-Octen-3-one (‘mushroom’ character)
• Detection threshold 20 ng/L
La Guerche et al., J. Agric. Food Chem. 2006, 54, 9193-9200.
Pons et al., J. Agric. Food Chem. 2011, 59, 3264-3272.
Sefton and Simpson, Austr. J. Grape Wine Res. 2005, 11, 226-240.
Concluding remarks
• Primary cause of musty taints
•
TCA and TBA
•
MDMP
• Contributor to musty taints
•
1-Octen-3-one
•
1-Methylisoborneol (possibly degrades)
•
Geosmin (possibly degrades)
• Small contributor to musty taints
•
2,4-DCA, 2,6-DCA, TeCA, PCA
Contact details
• Anita Oberholster
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RMI North, room 3146
aoberholster@ucdavis.edu
Tel: (530) 754-4866
http://wineserver.ucdavis.edu
http://enologyaccess.org