8C Volatile Compounds and Wine Aging 305
ethylphenols, mainly 4-ethylphenol and 4-ethylguaiacol, from the hydroxycinnamic
acid derivatives in the grapes (p-coumaric acid and ferulic acid) (Chatonnet et al.
1992b). The ethylphenol content in wine increases with aging time, especially
when aging takes place in used barrels. Ethylphenols have also been recorded
at lower concentrations in wines aged in new barrels (Chatonnet 1999; Pollnitz
et al. 2000; D ́ıaz-Plaza et al. 2002; P ́erez-Prieto et al. 2003; Garde-Cerd ́an and
Anc ́ın-Azpilicueta
2006). The highly porous nature of oak wood is favourable toBrettanomyces
growth, even in new barrels, and these yeasts are extremely hard to get rid of. Dif-
ferent methods of sanitizing barrels havebeen developed, from ozone sterilization
and the use of SO 2 (≥7g of SO 2 gas per barrel), to treating barrels with alternating
cycles of cold and hot (70◦C) water and low-pressure steam (10min) (Henick-Kling
et al. 2000; Malfeito-Ferreira 2005). Ozone sterilization results insmaller losses of
desirable volatile substances such as vanillin, oak lactones, and eugenol than the hot
water treatment commonly employed (Marko et al. 2005).
A series of chemical reactions, in particular oxidation, take place during bar-
rel aging, affecting both intrinsic wine components and those extracted from the
oak. Towey and Waterhouse (1996) did not observe any alterations in the fermen-
tation components during barrel aging, but other researchers have reported higher
acid and ester contents in wines aged in used barrels (P ́erez-Prieto et al. 2002).
The evaporation rate in these barrels is lower, because used barrels are less porous
due to deposits of mineral salts and colour compounds. Oxidation of certain wine
components inside the barrel gives rise tosuch important substances as acetalde-
hyde and phenylacetaldehyde while resulting in decreases in such alcohols (Jarauta
et al. 2005). The phenylacethaldehyde has been related to oxidation aromas that
present some aged wines (Aznar et al.2003). The formation of acetaldehyde during
wine aging is compensated by condensation reactions with polyphenols.
Wine lees and the barrel itself can adsorb certain wine volatiles and for that rea-
son may play an extremely important role in determining the aromatic composition
of the wine (Chatonnet et al. 1992a; Ram ́ırez Ram ́ırez et al. 2001; Jim ́enez Moreno
and Anc ́ın Azpilicueta 2007). Ram ́ırez Ram ́ırez et al. (2001) demonstrated that oak
wood could adsorb such volatile components as linalool and ethyl octanoate in a
model wine solution.
Lees aging is widely used, particularly for white wines or wines aged in new
barrels. Adsorption by the lees of substances released by the wood holds the
contribution of wood aromas down and prevents them from masking the other
wine aromas present. Eugenol, 4-propylguaiacol, 4-methylguaiacol, furfural, and
5-methylfurfural have high affinities for the lees, whereas high quantities of lees are
needed if there is to be any decrease in the concentrations of oak lactones and phe-
nolic aldehydes, namely, vanillin and syringaldehyde (Jim ́enez Moreno and Anc ́ın
Azpilicueta 2007).
At the end of barrel aging, wines ordinarily undergo further aging in the bot-
tle. During this period further chemical alterations that result in their final concen-
trations in the wine. For instance, concentrations of 5-methylfurfural and vanillin
have been observed to decrease while wine is in the bottle, probably due to the