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Chemistry of wood smoke

Lignin makes up 20 to 35% of the dry mass of wood. Pyrolysis differs from combustion and hydrolysis in that it usually does not involve the addition of other reagents such as oxygen. Guaiacol, or 2-methoxyphenol, is a common product of the pyrolysis of wood. Syringol, or 2,6-dimethoxyphenol, is a phenol with methoxy groups in the flanking 2 and 6 positions. Syringol is derived from the thermal decomposition of the sinapyl alcohol component of lignin. Sugarcane bagasse is one useful source of guaiacol; pyrolysis of the bagasse lignins yields compounds including guaiacol, 4-methylguaiacol and 4-vinylguaiacol.

Natural smoky materials

Birch bark tar is mainly composed of triterpenoid compounds of the lupane and oleanane family. Its most characteristic molecules are betulin and lupeol, which are also present in birch bark. Birch bark tar oil has strong antiseptic properties, owing to a large amount of phenol derivatives and terpenoid derivatives. Juniperus oxycedrus, vernacularly called cade, is a species of juniper native across the Mediterranean region. Cade oil is a dark, aromatic oil. Cade oil is used in some cosmetics and (traditional) skin treatment drugs, as well as incense. Wood tar is still used as an additive in the flavoring of candy, alcohol and other foods. Wood tar is microbicidal. Wood tar has been used as a preservative, water repellent, and antiseptic.

Smoke in food and wine

In preparation of food by smoking, guaiacol contributes mainly to taste. Artificial liquid or solid smoke flavorings also contain guaiacol and syringol. The main flavor compounds of smoked ham are guaiacol, and its 4-, 5-, and 6-methyl derivatives as well as 2,6-dimethylphenol. Guaiacol contributes to the flavor of many substances such as whiskey and roasted coffee. Liquid smoke is a water-soluble yellow to red liquid used as a flavoring to substitute for cooking with wood smoke.

Smoke taint is a wine fault attributable to exposure of grapes to smoke during the growing season. Wildfires in forested areas tend to burn a lot of wood, releasing volatile phenols into the atmosphere. The major volatile compounds responsible for smoke taint include guaiacol and methylguaiacol. Others include ortho-, meta- and para-cresol as well as syringol and methylsyringol.

Related Notes

Explore all seven extraits in the Discovery Set.