298 M.S. P ́erez-Coello and M.C. D ́ıaz-Maroto
The volatile composition of each barrel depends on its origin (species, geo-
graphic region, tree age, etc.), as well as on the different barrel manufacturing and
processing methods employed.
Quercus alba, also known as American white oak, and two European species,
Quercus roburL. andQuercus petraeaLiebl, the former also known as pedunculate
oak and the latter as sessile oak, are the species most frequently used in coopering.
On the whole, American oak is richer in oak lactones, especially in thecisisomer,
while European oak contains higher quantities of ellagitannins (Singleton 1995).
In the case of French oak, there are traditional differences between the vari-
ous regions, which ordinarily contain a single species, eitherQuercus petraeaor
Quercus robur. These regions are Allier, Limousin, Nevers, Vosges, Troncais, and
others. The oak woods from these regions can be differentiated on the basis of their
differing oak lactone, vanillin, andeugenol contents(Chatonnet 1998; P ́erez-Coello
et al. 1999).
However, large-scale studies have confirmed that there is high variability with
geographic origin, environmental factors, and growth factors. Using a sample set
of 400 American, French, and Eastern European trees, Prida and Puech (2006)
concluded that oak lactones and ellagitannins were the best substances to use as
variables for distinguishing between species, whereas eugenol, 2-phenylethanol, and
the phenolic aldehydes vanillin and syringaldehyde, which appeared at higher con-
centrations in oak wood samples from Eastern Europe, were the best components to
use as variables for distinguishing geographic origins.
Factors such as tree age decrease the amount of extractible substances in the
heartwood. At the same time, growth rate affects wood density. Growth rate depends
on the climate, type of soil, distance between trees, etc. (Singleton 1995). Coopers
prefer slow-growth (“fine-grain”) trees, because they are easier to cut and bend and
contain larger amounts of extractible substances and fewer ellagitannins. In any
event, recent studies didn’t find any correlation between the volatiles content and
ring width and have shown the botanical species to be the principal factor affecting
the amount of volatile substances present in oak wood (Doussot et al. 2000; Prida
et al. 2007).
Ordinarily,Q. petraeais the European species that contains the highest quantities
of oak lactones, furfurals, and phenolic aldehydes, though there is high diversity
according to geographical origin (Doussot et al. 2000, 2002; Guchu et al. 2006a;
Prida et al. 2007).
New types of oak wood from Eastern Europe (Ukraine, Russia, Romania, Hun-
gary, and others), also from the speciesQ. petraeaandQ. robur, have lately
entered the marketplace, alongside theFrench and American oak woods tradition-
ally employed for coopering. The volatile composition of this wood is similar to that
of French oak, and these sources may soon be competing with wood from traditional
sources. Little information on the composition of Eastern European oak wood is
available, though some recent work suggests that it contains higher amounts of phe-
nolic aldehydes and volatile phenols than French oak wood from the same species
and that its oak lactone content is intermediate between French and American oak
(Prida and Puech 2006).