Pluta

Origin

The cork oak, Quercus suber, is native to southwest Europe and northwest Africa. The montado landscape of Portugal produces approximately half of the cork harvested annually worldwide. The cork oak is a medium-sized evergreen tree and the primary source of cork for wine stoppers, flooring and the cores of cricket balls.

Composition

In general, cork is made up of suberin (average of about 40%), lignin (22%), polysaccharides (18%) and extractables (15%), among others. Suberin is a major constituent of cork and is named after the cork oak, Quercus suber. Suberin is a lipophilic, complex polyester biopolymer found in plants, composed of long-chain fatty acids and glycerol. Cork consists of dead, air-filled, thin-walled cells and contains cellulose and suberin. The cells of cork usually have a pentagonal or hexagonal shape. Cork is heat and sound insulating, and its suberin gives it water-repellent properties.

Uses

Because of its impermeable, buoyant, elastic and fire retardant properties, cork is used in a variety of products, the most common of which is wine stoppers. Natural cork closures are used for about 80% of the 20 billion bottles of wine produced each year. Cork is also used in construction, automotive and textiles. Aromatic compounds found in cork by-products and cork stoppers have been proposed for reuse as flavoring agents and antioxidants in the food industry.

Aromatic compounds

Twenty-three aromatic compounds were determined in granulates and cork samples. They belong to the families of vanillins and derivatives, volatile phenols, aldehydes, alcohols, terpenes, lactones, fatty acids and furans. Vanillin was the most important compound in the analysed samples, at up to 170 μg/g. 4-vinylguaicol was the most abundant volatile phenol. The terpenols found in cork include camphor, borneol, α-terpineol and 4-terpineol. A thermal desorption analysis of cork characterised 104 volatile organic compounds across samples from different geographical origins and manufacturing stages. Vanillin was the most abundant compound across all the geographical origins of cork analysed. Thermal treatment of cork stoppers raised the levels of ketones such as acetophenone and 2-nonadecanone and lowered certain alkanes and fatty acids.

Cork taint

Cork taint is a wine fault, an off-odor and off-flavor, arising from aroma-intense compounds present in the cork that are transferred into wine after bottling. 2,4,6-Trichloroanisole (TCA) has been identified as the primary chemical responsible for cork taint. An estimated 80-85% of all cork taints are due to TCA. The estimated share of affected bottles is between 1% and 5%. TCA is formed by the methylation of 2,4,6-trichlorophenol. It may also be produced when naturally occurring airborne fungi and bacteria are presented with chlorinated phenolic compounds, which they then convert into chlorinated anisole derivatives. TCA has the molecular formula C₇H₅Cl₃O and the IUPAC name 1,3,5-trichloro-2-methoxybenzene. A worldwide loss of roughly US$1 billion per year is attributed to cork taint in wine.

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