# Chemical Migration from Wine Contact Materials
## 4 Chemical Substances Migrating to Wine
Most of these volatile compounds are metabolites produced in the presence of microorganisms either on the cork or in its environment and subsequently absorbed by the cork and eventually transferred to wine after sealing. The precursors of these metabolites may be naturally occurring substances like lignin in the case of guaiacol and lipids in the case of 1-octen-3-ol and 1-octen-3-one, or pesticides and biocides such as 2,4,6-trichlorophenol and other chlorophenols used as wood preservatives or plant protection products in the case of trichloroanisole (2,4,6-TCA) [63]. Furthermore, the formation of 2,4,6-TCA and other chlorinated compounds has been related to the bleaching of corks, and it is considered to occur by chlorination of lignin compounds [63]. In particular, the mechanism of 2,4,6-TCA formation has been reported to involve microbial O-methylation of chlorophenols and chlorination of anisole [70]. It is noted that apart from the migration from contaminated cork stoppers or barrels, other origins of contamination of wine with these substances include the air pollution of the cellars [62; 70] or the use of contaminated grapes [62; 68]. Apart from the naturally occurring substances in corks or the metabolites of naturally occurring substances and degradation products of environmental contaminants like bleaching reagents and pesticides, there are other substances used in the manufacture of wine contact materials that could potentially migrate into wine. These contact materials include treated corks, stoppers, plastic bottles, cans, and paper bags, and the migrating substances concern antioxidants, lubrications, monomers, and plasticizers [35; 36; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80]. These substances are related more to wine safety issues since they include compounds that have been related to human health risks, such as bisphenol A (BPA), which has been characterized as a potential endocrine-disrupting compound [81], and certain phthalates which have been classified for their toxicity according to Regulation (EC) No 1272/2008 [82], and other substances of raised concern which are included in the EU control plan for certain substances migrating from materials and articles intended to come into contact with food [83]. Based on the above, the following classification is proposed for the chemical substances migrating to wine, according to their origin, as illustrated in Figure 1:  
(i) Substances related to the industrial manufacture of wine contact materials: substances related to the manufacturing and use of plastics and glass (intentionally added substances and non-intentionally added substances, including micro and trace elements and microplastics). (ii) Natural occurring substances and microbial degradation products of environmental contaminants  
It is noted that micro and trace elements may originate naturally in packaging materials like cork and glass, or they may originate from the manufacturing of polymers and plastics. The study of the migration of these substances is implemented by migration tests in order to investigate their transfer from the wine contact material into wine and, afterward,the application of specific analytical techniques for their identification and quantification in wine or wine simulant. Alternatively, the occurrence of suspect migrating substances is examined by direct analysis of wine without the application of a migration test. The present review of analytical methods focuses on the determination of the chemical substances that belong to category (i), namely substances related to the industrial manufacture of wine contact materials and are usually related to safety issues.