A wide range of distilled beverages, including whisky and
cognac, continue to be matured for many years in oak
barrels. During maturation a range of physical and chemical
interactions take place between the barrel, the surrounding
atmosphere and the maturing spirit which transform both
the ¯avour and composition of the drink. The eects and
time required for maturation are highly variable and are
in¯uenced by a wide range of factors, particularly the type
of barrel used. As our understanding of the process has
improved there has been increasing interest in methods of
predicting, controlling and simulating the eects of
maturation. # 1998 Elsevier Science Ltd. All rights reserved
Ageing is among the most important and the most
costly factors in¯uencing the quality of distilled bev-
erages. A wide range of distilled alcoholic drinks are
now matured in oak casks, most notably whiskies and
brandies but also many rums and liqueurs. While prob-
ably originally serving only as a means of storage and
transportation, the time spent in the oak cask is now
seen as fundamentally contributing to the ®nished taste
and aroma.
Both the type of cask and the duration of maturation
vary widely and are frequently de®ned by international
or local statutes according to the product name. Thus,
American corn whisky must be matured in new charred
barrels, while in Canada and Scotland maturation must
be for a minimum of 3 years with many malts matured
for 12 or more years. The size of the cask varies from
190 litre American barrels to 558 litre puncheons [1].
Larger vats may be used for storage or delivery but not
true ageing. With an estimated 13 million casks in use
for the maturation of Scotch whisky, 3 million esti-
mated to be found within a 25 kilometre distance of the
town of Cognac and with approximately a million casks
produced every year by the American cooperage indus-
try, most destined for the maturation of Bourbon, it is
not dicult to grasp the scale of investment that this
stage in the production of distilled beverages entails.
Maturation of beverages
The process of maturation and ageing is characterized
by changes in the colour and ¯avour of the maturing
spirit and a decline in both the volume and the alcoholic
content. The time required for satisfactory maturation
varies according to the characteristics of the raw dis-
tillate, the size, wood origins and treatment of the cask
and the environment in which the spirit is matured.
The change in the ¯avour of the maturing spirits is
due to changes in the composition and concentration of
compounds in¯uencing the taste and aroma. These
changes may be caused by [2]:
.
Direct extraction of wood compounds;
.
Decomposition of wood macromolecules and
extraction of their products into the distillate;
.
Reactions between wood components and the
constituents of the raw distillate;
. Reactions involving only wood extractives;
. Reactions involving only the distillate compo-
nents;
. Evaporation of volatile compounds.
The extraction and subsequent transformation of
compounds from the oak cask is believed to be of prime
importance to the ®nal ¯avour.
Figure 1 describes the variety of extractive and struc-
tural compounds that make up oak heartwood. The
most abundant extractives, found in unheated wood,
are the ellagitannins. Despite these hydrolysable tannins
being highly soluble in ethanol-water solutions, ellagi-
tannins are not found in spirits matured in oak casks [3±5].
While rapidly degraded during the heating of wood, this
cannot explain their total absence in spirits as unheated
wood is also exposed to extraction. Puech et al. (sub-
mitted for publication) recently found that the decline in
ellagitannins stored in ethanol±water solutions coincides
with the addition of ethoxy moities.This transformation
is probably followed by further rearrangements during
the ageing of spirits. While frequently claimed to in¯uence
0924-2244/98/$19.00 Copyright # 1998 Elsevier Science Ltd. All rights reserved
PII: S0924-2244(98)00024-7
Trends in Food Science & Technology 9 (1998) 95±101
Wood maturation
of distilled
beverages
J.R. Mosedale and J-L. Puech
Institut des Produits de la Vigne, INRA, 2 place Viala,
34060 Montpellier, France (fax: +33-04-9961-2683;
e-mail: mosedale@ensam.inra.fr)
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