**6. Off-flavors and beneficial compounds**

One of the most important taints in wine is a moldy taste and aroma due to the presence of haloanisoles, namely, of 2,4,6-trichloroanisole (TCA), traditionally named as corkiness or cork taint. The olfactory detection threshold (ODT) of TCA is very low (1–4 ng/L) although variable depending on the consumer, the type of wine, and the occasion at which it is consumed, among other factors.

TCA is a nonpolar compound that has a large affinity for lipids such as those found in cork (monomeric extractives and polymeric suberin) that therefore can absorb TCA as well as other chloroanisoles [3]. The accumulation of chloroanisoles and chlorophenols in cork could be related to the use of polychlorinated phenolic biocides in forest, the chlorine bleaching of cork, the hypochlorite washing of wine barrels, the use of chlorinated phenolic biocides in packaging material, and the environmental contamination of wine cellars [3]. Therefore, the contamination sources have been eliminated in the cork industry in the last years. The International Code of Cork Stopper Manufacturing Practices prohibits nowadays the use of chlorine and other materials containing this compound at any stage of stopper production in order to reduce the possibility of chlorophenol development. Stoppers are currently washed with hydrogen peroxide as means of disinfecting and whitening.

Once the TCA can have origin in microbial sources (such as yellow stain), cork industry implemented new and changed old procedures aiming at the elimination of microbial contamination: the cork planks are screened before processing and during the process line for the elimination of those that contain signs of microbial activity; the industrial yards are nowadays cemented to avoid the contact of cork planks with soil in the preprocessing storage; and the time was decreased and the conditions controlled for the storage between the boiling of cork planks and their processing into stoppers.

In addition to the recognized standards in the International Code of Cork Stopper Manufacturing Practices, other processes to eradicate TCA have been implemented by companies in the sector: new boiling systems, controlled steam distillation, volatilization by dragging a controlled temperature and humidity, volatilization by dragging in the gaseous phase of adjusted polarity, under controlled temperature and humidity, and supercritical extraction with CO2 [51].

Quality control of cork stoppers also increased, with procedures given by standard protocols, for example, ISO 20752:2014 specifies a test method to determine releasable TCA from cork stoppers, and ISO/PRF 22308 specifies a method for detecting and quantifying by sensory analysis several aromas including mold. The Cork Quality Council in the USA developed a research project using SPME-GC/ MS analysis which allows technologically complex and very sensitive equipment to be used in the quantification of TCA in cork lots. Recently, Amorim launched NDtech, a natural cork that they guarantee with a nondetectable TCA (releasable TCA content at or below the 0.5 ng/L quantification limit; analysis performed in accordance to ISO 20752), based on the deployment of fast and unitary cork stopper chromatography.

**235**

**Vanillins**

**Volatile phenols**

**Aldehydes**

*Cork and Cork Stoppers: Quality and Performance DOI: http://dx.doi.org/10.5772/intechopen.92561*

tal TCA contamination [52].

epicatechin, and quercetin) [54].

from oak wood or cork into the wine.

of extrinsic tannins in commercial products [57].

aromatic family in cork extracts (**Table 3**).

In addition, research studies demonstrated that TCA does not permeate through cork showing that cork stoppers can act as an effective barrier against environmen-

Extrinsic sources of phenolic compounds found in wine include the barrels used in oak aging and cork stoppers, where small molecules are susceptible to migration

Cork polyphenols were reported to migrate into wine after bottling, which may benefit the aging of wine through the release of phenolics and volatiles from the structure of the closure. In recent years, various studies have been carried out to analyze the intrinsic chemical features of cork regarding its advantages to health. The phenolic composition of cork has been studied, and several polyphenols were identified in cork: low molecular weight polyphenols such as acids, aldehydes, flavanones, and coumarins; hydrolysable tannins; and highly antioxidant molecules, such as gallotannins and ellagitannins and condensed tannins [55, 56]. Hydrolysable tannins are not naturally present in grapes, and their presence in wine stems from enological practices such as oak aging and natural wood extraction or the addition

Polyphenols are easily extracted by a hydroalcoholic solution [55] and may react with the main components of wine [58], impacting on color and sensory properties of a bottled wine such as odor, flavor, and astringency. Azevedo et al. [59] identified and quantified the phenolic compounds from cork that were able to migrate from different cork stoppers to wine model solutions during 27 months. The phenolic compounds that solubilized in higher amounts were gallic acid, protocatechuic acid and aldehyde, and vanillin, while in lesser amounts, more complex structures have migrated such as valoneic acid, ellagic acid pentose, and castalagin/vescalagin. Mislata et al. [60] characterized the aromatic composition of different wine cork stoppers and granulates, reporting that vanillins are by far the most important

**Aromatic compound Aromatic descriptor Content (μg/g)**

Vanillin Vanilla 9–170 Acetovanillone Vanilla 0.6–14

Guaiacol Wood, smoked, sweet, medicine 0.03–5.0 4-Vinylguaiacol Wood, spice cloves, curry 0.5–23 Eugenol Spice cloves, honey 0.01–0.3 Isoeugenol Carmination 0.06–2.4 Cerulignol Spicy 0.04–2.2

Benzaldehyde Almonds, sweet, caramel 0.02–0.21 Nonenal Wax, citrus 0.03–0.47 Phenylacetaldehyde Green, grass, honey 0.05–4.5

Wine is, from a chemical point of view, a very complex fluid composed of a mixture of water, alcohols, organic acids, phenolic compounds, sugars, amino acids, and various minerals [53]. Several phenolic compounds present in wine, especially red wine, have gathered scientific interest in medical applications, including nonflavonoid phenolic acids (coumaric, cinnamic, caffeic, ferulic, and vanillic acids), trihydroxy stilbenes (resveratrol and polydatin), and flavonoids (catechin,

*Cork and Cork Stoppers: Quality and Performance DOI: http://dx.doi.org/10.5772/intechopen.92561*

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

through the plasmodesmata) present in the cork cell walls [47].

wine, and the occasion at which it is consumed, among other factors.

**6. Off-flavors and beneficial compounds**

were bored out of cork planks with 27–32 and 45–54 mm calipers, respectively, representing 36–38 and 47–50% of the theoretically total oxygen present in the cell structure. Moreover, Oliveira et al. [34] suggested that the high oxygen ingress rates immediately after bottling are due to the transfer of the air trapped in the voids in the bottom part of the cork stopper. After this first period, gas transport through the cork cells occurs with very low diffusion rates through small channels (i.e.,

One of the most important taints in wine is a moldy taste and aroma due to the presence of haloanisoles, namely, of 2,4,6-trichloroanisole (TCA), traditionally named as corkiness or cork taint. The olfactory detection threshold (ODT) of TCA is very low (1–4 ng/L) although variable depending on the consumer, the type of

TCA is a nonpolar compound that has a large affinity for lipids such as those found in cork (monomeric extractives and polymeric suberin) that therefore can absorb TCA as well as other chloroanisoles [3]. The accumulation of chloroanisoles and chlorophenols in cork could be related to the use of polychlorinated phenolic biocides in forest, the chlorine bleaching of cork, the hypochlorite washing of wine barrels, the use of chlorinated phenolic biocides in packaging material, and the environmental contamination of wine cellars [3]. Therefore, the contamination sources have been eliminated in the cork industry in the last years. The International Code of Cork Stopper Manufacturing Practices prohibits nowadays the use of chlorine and other materials containing this compound at any stage of stopper production in order to reduce the possibility of chlorophenol development. Stoppers are currently washed with hydrogen peroxide as means of disinfecting and whitening. Once the TCA can have origin in microbial sources (such as yellow stain), cork industry implemented new and changed old procedures aiming at the elimination of microbial contamination: the cork planks are screened before processing and during the process line for the elimination of those that contain signs of microbial activity; the industrial yards are nowadays cemented to avoid the contact of cork planks with soil in the preprocessing storage; and the time was decreased and the conditions controlled for the storage between the boiling of cork planks and their

In addition to the recognized standards in the International Code of Cork Stopper Manufacturing Practices, other processes to eradicate TCA have been implemented by companies in the sector: new boiling systems, controlled steam distillation, volatilization by dragging a controlled temperature and humidity, volatilization by dragging in the gaseous phase of adjusted polarity, under controlled

Quality control of cork stoppers also increased, with procedures given by standard protocols, for example, ISO 20752:2014 specifies a test method to determine releasable TCA from cork stoppers, and ISO/PRF 22308 specifies a method for detecting and quantifying by sensory analysis several aromas including mold. The Cork Quality Council in the USA developed a research project using SPME-GC/ MS analysis which allows technologically complex and very sensitive equipment to be used in the quantification of TCA in cork lots. Recently, Amorim launched NDtech, a natural cork that they guarantee with a nondetectable TCA (releasable TCA content at or below the 0.5 ng/L quantification limit; analysis performed in accordance to ISO 20752), based on the deployment of fast and unitary cork stopper

temperature and humidity, and supercritical extraction with CO2 [51].

**234**

chromatography.

processing into stoppers.

In addition, research studies demonstrated that TCA does not permeate through cork showing that cork stoppers can act as an effective barrier against environmental TCA contamination [52].

Wine is, from a chemical point of view, a very complex fluid composed of a mixture of water, alcohols, organic acids, phenolic compounds, sugars, amino acids, and various minerals [53]. Several phenolic compounds present in wine, especially red wine, have gathered scientific interest in medical applications, including nonflavonoid phenolic acids (coumaric, cinnamic, caffeic, ferulic, and vanillic acids), trihydroxy stilbenes (resveratrol and polydatin), and flavonoids (catechin, epicatechin, and quercetin) [54].

Extrinsic sources of phenolic compounds found in wine include the barrels used in oak aging and cork stoppers, where small molecules are susceptible to migration from oak wood or cork into the wine.

Cork polyphenols were reported to migrate into wine after bottling, which may benefit the aging of wine through the release of phenolics and volatiles from the structure of the closure. In recent years, various studies have been carried out to analyze the intrinsic chemical features of cork regarding its advantages to health. The phenolic composition of cork has been studied, and several polyphenols were identified in cork: low molecular weight polyphenols such as acids, aldehydes, flavanones, and coumarins; hydrolysable tannins; and highly antioxidant molecules, such as gallotannins and ellagitannins and condensed tannins [55, 56]. Hydrolysable tannins are not naturally present in grapes, and their presence in wine stems from enological practices such as oak aging and natural wood extraction or the addition of extrinsic tannins in commercial products [57].

Polyphenols are easily extracted by a hydroalcoholic solution [55] and may react with the main components of wine [58], impacting on color and sensory properties of a bottled wine such as odor, flavor, and astringency. Azevedo et al. [59] identified and quantified the phenolic compounds from cork that were able to migrate from different cork stoppers to wine model solutions during 27 months. The phenolic compounds that solubilized in higher amounts were gallic acid, protocatechuic acid and aldehyde, and vanillin, while in lesser amounts, more complex structures have migrated such as valoneic acid, ellagic acid pentose, and castalagin/vescalagin. Mislata et al. [60] characterized the aromatic composition of different wine cork stoppers and granulates, reporting that vanillins are by far the most important aromatic family in cork extracts (**Table 3**).



#### **Table 3.**

*Aromatic compounds, families, descriptors, and minimum and maximum content found in the studied granulates and cork macerates [60].*
