8C Volatile Compounds and Wine Aging 297
Cellulose, hemicellulose, and lignin are insoluble substances, but some of their
monomers can be partially extracted in hydroalcoholic solutions like wine. Some
of the compounds thus extracted have interesting organoleptic qualities (Boidron
et al. 1988).
The remaining wood components make up the fraction that can be extracted
with different solvents, mainly comprising volatile and non-volatile acids, sug-
ars, steroids, hydrolysable tannins (ellagitannins), volatile phenols, terpenes, lac-
tones, etc. This review will deal withthe volatile components that can leach out
into the wine during barrel aging and as a result may affect the sensory attributes
of wine.
The two oak lactone isomers (cis-andtrans- -methyl--octalactone) were first
identified in oak wood by Masuda and Nishimura (1971). They are one of the main
volatile components present in the extractible fraction of oak wood. Studies have
revealed the detection thresholds for these two isomers to be 0.092mg/L for thecis
isomer and 0.49mg/L for thetransisomer in white wines (Chatonnet 1991). Their
aroma has been identified as the source of the typical odour of oak barrel aging and
has been described as “oak” or “coconut”.
The major phenolic aldehydes, vanillin and syringaldehyde and their derivatives
(coniferaldehyde, sinapaldehyde, acetovanillone, acetosyringone, and others) come
from fragments of lignin arising throughhydrolysis, pyrolysis, and oxidation reac-
tions. Vanillin is the only one of these that influences wine aroma. It has a character-
istic vanilla flavour with an olfactory detection threshold of 0.32mg/L in red wine
(Boidron et al. 1988). Guaiacol and its 4-ethyl and 4-vinyl derivatives along with
eugenol and isoeugenol are the main volatile phenols that have a sensory impact on
wines aged in the wood. The former group contributes spicy, toasted, and smoky
aromas, while the latter impart characteristic spicy, clove, and oak aromas (Boidron
et al. 1988).
Terpenes and norisoprenoids, including linalool and its derivatives, -terpineol,
geranyl acetone, -ionone and its derivatives, 3-OH- -damascone, blumenol, vom-
ifoliol, spathulenol, and vulgarol have been identified in oak wood samples having
different origins. These substances were more abundant in samples of American oak
than in samples of French oak (Sefton et al. 1990; P ́erez-Coello et al. 1998). Certain
of these components have interesting fruity and floral aromas in the case of terpenes
and tobacco, or woody aromas for some norisoprenoids. Many of them are present
in the grapes and in wine, but there has been little research on their presence in
wines during aging, which gives rise to a series of uncertainties as to their effects on
the aroma of oak wood barrel aged wines.
Other volatile compounds present in oak wood can transmit unpleasant aro-
mas to the wine, such as the “sawdust” aroma of dry wood that is perceptible in
some wines aged in new barrels. The substances that cause these aromas have been
identified in both American and European oak wood, for instance, (E)-2-nonenal,
3-octen-1-one, (E)-2-octenal, and 1-decanal. Their connection with the “sawdust”
aroma has been established by olfactometry, and they have been identified in wines
suffering from this flaw, though toasting the wood (Chatonnet and Dubourdieu
1998).