*Wine Stabilisation: An Overview of Defects and Treatments DOI: http://dx.doi.org/10.5772/intechopen.95245*

*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

via another source for example from trees.

1,8-Cineole (eucalyptol, XXVIII, **Figure 1**) is known to give the perception of eucalyptus and minty flavour, not negative sensory notes by themselves, the reason why there is a discussion if it should be considered as a positive or as a taint in red wine. The sensory perception threshold is very low, of 1.1 μg/L, and a recognition threshold of 3.2 μg/L in Californian Merlot wine [107]. Farina et al. [108] reported similar threshold values in Uruguayan Tannat wine. According to Saliba et al. [109], the mechanism by which 1,8-cineole occurs in the finished wine is not well understood and three mechanisms have been suggested: the compound develops from chemical precursors during the winemaking and bottle ageing processes, namely by chemical transformation of limonene and α-terpineol [108]; that grapes naturally produce the compound during berry development [110]; 1,8-cineole is introduced

Geranium taint is due to the presence of 2-ethoxy-3,5-hexadiene (XXIX, **Figure 1**) in wine, which has an odour reminiscent of crushed geranium leaves. It is originated from the reduction of sorbic acid carried out by the LAB. The reduction product sorbitol under wine conditions isomerises to 3,5-hexadiene-2-ol that after reaction with ethanol generates the 2-ethoxyhexa-3,5-diene which has a sensory threshold of

Grapevines and grape exposure to smoke from firers can result in wines with undesirable sensory characters, such as 'smoky', 'burnt', 'ashy' or 'medicinal', usually described as 'smoke taint'. Smoke taint markers in grapes and wine are the VPs, guaiacol (XXX, **Figure 1**), and 4-methylguaiacol (XXXI, **Figure 1**) [112]. Kennison et al. [113], showed that trace levels (≤1 μg/L) of guaiacol, 4-methylguaiacol, 4-ethylguaiacol and 4-ethylphenol were detected in grape juice derived from grapes harvested from grapevines exposed to smoke; but significant quantities of these phenols were released when the grape juice was fermented, or hydrolysed with strong acid or β-glucosidase enzymes. These compounds are known to exhibit 'smoky', 'phenolish', 'sharp', and 'sweet' aromas [113]. Guaiacol causes a phenolic and medicinal taint in a contaminated wine [114], its flavour threshold is 0.030 mg/L in an aqueous solution containing 12% ethanol. An aroma threshold of 0.020 mg/L in a dry white wine was reported by Simpson et al. [115] and a detection threshold in the water of 5.5 μg/L and white wine of 95 μg/L and red wine,

2,4,6-trichloroanisole (TCA, XXXII, **Figure 1**) is probably the most known compound associated with wine defect, being the key compound responsible for the 'cork taint' in wines [116]. It is very easy to recognise because of its low sensory threshold, which is from 0.03 to 1–2 ng/L in water and 4 ng/L in white wine for trained assessors. However, the threshold values in wine depend strongly on the kind of wine, the wine style, and the experience of the panellist [117]. 'Cork taint' is mostly described as a musty, mouldy, or earthy smell, being sometimes also described as burnt rubber, smoky or even camphor. Other chloroanisoles, such as 2,4-dichloroanisole (2,4-DCA, XXXIII, **Figure 1**), 2,6-dichloroanisole (2,6-DCA, XXXIV, **Figure 1**), 2,3,4,6-tetrachloroanisole (TeCA, XXXV, **Figure 1**) and pentachloroanisole (PCA, XXXVI, **Figure 1**) can also contribute to the 'cork taint' but they do not play a dominant role in this fault. 2,4,6-tribromoanisole (TBA, XVII, **Figure 1**) can also have a significant role in the musty/mouldy of-odour of wines [118]. Moreover, the aroma masking effect of TCA or TBA can be perceived in the wines at levels even lower than perception thresholds (4 ng/L) [118]. As cork is a natural product from the cork oak it is subject to microbial contamination and its quality is dependent on good agricultural practices and quality control during processing, transport, and storage. Chlorophenolic biocides

**3.2 Wine taints**

about 0.1 mg/L [111].

75 μg/L [112].

**184**

(nowadays forbidden but accumulated in the environment) are the common precursors which can be transformed by certain fungi to TCA and different chloroanisoles. Other pathways of chloroanisoles formation usually include reactions of chlorination and methylation of compounds naturally present in wooden and cork materials [119]. At the same time 2,4,6-tribromophenol (TBP), which application is not restricted present, can play the role of TBA precursor and increases the risk of musty/mouldy taint in wines [118]. Moulds are considered the most significant causative organisms of cork taint, with implicated genera including *Penicillium*, *Aspergillus*, *Cladosporium*, *Monilia*, *Paecilomyces* and *Trichoderma*. Nevertheless, the process of wine contamination by haloanisoles is complex. Since cork stoppers are the most known source of these compounds, the musty/mouldy fault was named 'cork taint'. However, succeeding studies demonstrated that musty/mouldy defects in wine are not originated exclusively from the naturally contaminated cork materials [118, 120]. TCA and other haloanisoles can be formed in different wooden parts inside the cellar (barrels, ceiling constructions, pallets) and subsequently released into the air. Hereafter, the contamination of winery equipment and 'clean' cork stoppers occurs and haloanisoles can be transmitted further to the wine. Besides, cork taint-related flavours were found in wines that were barrel samples or not closed with natural cork stoppers, indicating that natural cork stoppers are not the only source of mouldy off-flavours [118, 120]. Therefore, depending on the compound causing the cork taint, the consumer has a different impression of the problem. Several compounds with similar negative flavour attributes were discovered in mouldy and musty smelling wines that were not affected by TCA (geosmin, 2-methyl-isoborneol, octane-3-one, pyrazines, etc.) [121]. That said, misguided hygiene practices have historically been part of the cork-taint problem. Cleaning using chlorinated bleach was common in wineries until a link to cork taint was found. Contact between barrels and bleach on cellar floors was a particular pathway for TCA to strike. Flame-retardant paints and fungicides were found to taint wine with TBA. Barrelled wines were particularly badly hit, and some facilities had to be rebuilt. Nowadays most wineries know to avoid chemicals containing tribromophenols. Heat-treated wood is more common, and barrels are rarely cleaned with chlorine. Different approaches were made regarding the removal of TCA and TBA from tainted wines; either by fining with ACs and filtered afterwards, or polyethylene was added as an adsorbent to the wine [121].

Along with TCA and TBA, geosmin (XXXVIII, **Figure 1**), 2-methylisoborneol (MIB XXXIX, **Figure 1**), 1-octen-3-one (XL, **Figure 1**) and 1-octen-3-ol (XLI, **Figure 1**) are compounds that are closely linked with the growth of moulds [116]. Their presence in wines can impart typical earth, mushroom, fungal and mouldy flavour [122, 123]. The mushroom aroma is associated mainly with 1-octen-3-one and 1-octen-3-ol, whereas the earthy aroma is attributed to (−)-geosmin and an earthy-camphor aroma to 2-methylisoborneol. Geosmin may result from the development in grapes picked in unfavourable weather conditions by microorganisms. It is a chiral compound and the (−) form is much more odoriferous than the (+) form. (−) Geosmin is also the only enantiomer to have been identified in pure cultures of *Streptomyces* sp. and *Penicillium* sp. strains isolated from rotten grapes [121]. Geosmin olfactory detection threshold depends on the wine matrix: In water: 10 ng/L [122]; In wine: white wine, 60–65 ng/L [122]; red wine, 80–90 ng/L [122]. MIB is a metabolite of *Botrytis cinerea*, some *Penicillium* spp. and some *Streptomyces* spp. MIB and 1-octen-3-one have also been found in musts made from rotten grapes but not in the corresponding wines, indicating that they are not stable during AF [123]. The findings of both compounds in bottled wine can therefore be linked to the cork stopper and the growing of mould on the cork during the manufacturing process. MIB olfactory detection threshold has been determined as: 0.012 μg/L (in

water La Guerche et al. [123]; 0.04 μg/L [123]; in red wine). 1-octen-3-ol (olfactory detection threshold in the water of 2 μg/L and red wine, 40 μg/L, La Guerche et al. [123], however, has also been found on rotten grapes and the musts made from them and is stable during AF so that an occurrence of this compound in a wine can be caused by mould growth on the grapes as well as by contaminated cork stoppers [124]. Lisanti et al. [125] showed that in the red wine the potassium caseinate and grape seed oil treatments decreased the level of geosmin by 14% and 83%, respectively, while in the white wine, the AC and the grape seed oil were able to decrease the level of geosmin by 23% and 81%, respectively. However, after estimating the olfactory impact of the volatile compounds by OAVs (concentration/odour perception threshold), only the treatment with grape seed oil was able to decrease the relative contribution of geosmin in the profile of the odour active compounds, in both wines.

Wine can accidentally be contaminated with styrene when trace amounts of the styrene (XLII, **Figure 1**) are released during wine storage in polyester tanks reinforced with fibre glass [126]. Also, occasionally styrene contamination has been detected in wine in contact with synthetic closures [127]. The taste threshold for styrene in water has been reported as 22 μg/L [128] but may be higher in wine. An amount higher than 100 μg/L (the generally accepted threshold of sensory perception), styrene can modify the wine sensory characteristics by imparting a taste of plastic and adhesive. Wagner et al. [129] found in German wines values ranging from 0 to 19 μg/L.
