Odorants in oak wood - a review of aroma-analytical approaches used for uncovering the olfactorily relevant substances

Oak wood has been used for centuries in the production of alcoholic beverages to induce desired sensorial aroma notes during the aging process. To explore the influence of oak on the aroma profiles of alcoholic beverages like wine, a series of influencing factors has been investigated, such as storage and thermal treatment of the oak barrels, tank staves or chips, as in seasoning, toasting or charring. These investigations resulted in comprehensive data on aroma compounds in wine maturated in oak barrels. Strategies to unveil the impact of oak wood on the aroma of beverages such as wine commonly comprise human sensory analyses, odorant recovery via extraction and distillation using techniques such as solvent-assisted flavor evaporation (SAFE), and targeted odorant identification, mostly applying a combination of human sensory and chemo-analytical techniques. In aroma analysis regarding foods and beverages, a systematic analytical concept is established since decades, comprising, in most cases, aroma extract dilution analysis (AEDA), which is based on gas chromatography-olfactometry (GC-O). Commonly, the odorants are identified via gas chromatography-mass spectrometry/olfactometry (GC-MS/O) and heart-cut two-dimensional gas chromatography-mass spectrometry/olfactometry (2D-GC-MS/O). The majority of the odorants reported to date as being associated with oak-wood in the context of alcoholic beverages comprise a series of terpenes, mainly mono- and sesquiterpenes, aldehydes, acids, lactones and a number of odorants containing a phenolic core moiety. The successful identification of these odorants creates a better understanding of the unique smell of oak wood, and helps unveiling its potential benefits in different applications.