Chemical, sensory and consumer analysis of cork taint in South African wines
Date
2009-03
Authors
Van Eeden, Petrus Rabe
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
This study focused on a serious quality-related problem in the global wine industry, including
the South African Wine Industry, namely cork taint in wine. Annually, large financial losses
are incurred by cork suppliers and wine producers, as a result of cork-tainted wine. Although
contaminated new unused corks are frequently implicated as the origin of this taint,
contaminated cellar equipment and water can also be the source of the problem.
An explorative investigation into the incidence of cork taint in South African wines showed
that 3.8% of the 133 wines tested, contained 2,4,6-trichloroanisole (TCA) concentrations of
3.5 ng/L and higher, as determined by gas chromatography coupled with electron capture
detection (GC-ECD). TCA concentrations higher than 1 ng/L were found in 18% of the wines
tested. All affected wines were sealed with solid or agglomerate cork stoppers. These wines
were sourced from various wineries in the Western Cape region, South Africa and were of
different cultivars. None of the wines sealed with synthetic closures had any detectable TCA,
2,4,6-tribromoanisole (TBA) or pentachloroanisole (PCA) levels and only very low 2,3,4,6-
tetrachloroanisole (TeCA) levels (1 ng/L or less). Another group of 28 wines that were
rejected by the official South African wine regulatory body on the basis of the presence of
mouldy taint during wine certification, was also included in this study. GC-ECD analysis
showed that 30% of the wines in this group contained TCA at concentrations of 3.5 ng/L and
higher. These results pointed to a relative high incidence of TCA in the wines investigated,
especially those sealed with cork stoppers. Although no general conclusions should be made
on the incidence of cork taint in the wider wine industry based on the results found within this
explorative investigation, these findings confirmed the presence of cork taint in South African
wines.
Detection threshold values were determined for TCA, TeCA, TBA and PCA in three wine
cultivars using the standard ASTM method. Results indicate that factors relating to the wine
cultivar seemed to affect threshold values considerably. Our research proposes a detection
range rather than an average detection threshold. Detection ranges established for TCA,
TeCA, TBA and PCA in Chenin blanc, Pinotage and Shiraz coincide with reported values in
literature. This result can be regarded as a valuable expansion of the existing knowledge of
detection threshold values.
Descriptive sensory analysis indicated significant (P 0.05) changes in the aroma profile of
Chenin blanc, Pinotage and Shiraz after TCA, TeCA, TBA or PCA was added to the respective base wines that contained no detectable levels of the haloanisoles. The mouldy
taint induced by these haloanisoles were described as mouldy, mouldy-chemical, mouldychlorine,
as well as mouldy-acidic. In Chenin blanc, additions of TCA, in the concentration
range 1 to 17 ng/L, resulted in a marked increase in the mouldy aroma and was
accompanied by an immediate decrease in fruitiness. This change was already evident at
added TCA concentrations of 1 ng/L. Similar trends were observed in Pinotage, while the
addition of low levels of TCA to Shiraz (2 ng/L) resulted in a significant (P 0.05) decrease in
the herbaceous character of the wine. The aroma changes observed were prominent
enough to render the wine totally unacceptable in comparison to its original character.
Consumers’ degree of liking did not seem to be affected by very low concentration levels of
TCA in Chenin blanc, Pinotage or Shiraz, but rejection increased as the concentration
increased beyond detection threshold level. A slight gender effect was also noticed. Female
consumers appeared to be more sensitive to increasing levels of TCA, whereas male
consumers did not respond as negatively to higher concentration levels of TCA.
This study makes an important contribution towards understanding the sensory impact of
especially TCA contamination in wine, through the establishment of concentration ranges at
which these compounds exert a noticeable detrimental effect on the aroma profile of wine.
Additional insight into cork taint in wine is provided by the consumer preference studies,
where the effects of the taint on the product acceptance by consumers are demonstrated.
The development of a modus operandi to ensure that sensory panels provide reliable data,
can be regarded as an important contribution to wine-related research. This study is one of
the first where advanced sensometric techniques were applied in sensory studies on cork
tainted wines.
Description
Thesis (MSc Food Sc (Food Science))--University of Stellenbosch, 2009.
Keywords
Cork taint, Dissertations -- Food science, Theses -- Food science