Volatile composition of oak and chestnut woods used in brandy ...

Abstract
Volatile composition of oak and chestnut woods used in
brandy ageing: Modification induced by heat treatment
Ilda Caldeira a, *, M.C. Clímaco a , R. Bruno de Sousa b , A.P. Belchior a
a INIAP-Estação Vitivinícola Nacional, 2565-191 Dois Portos, Portugal
b Instituto Superior de Agronomia, Departamento de Química Agrícola e Ambiental, Tapada da Ajuda, 1349-017 Lisboa, Portugal
Received 11 December 2004; accepted 10 May 2005
Available online 5 July 2005
The volatile composition (26 compounds) of seven different types of wood (6 oaks and 1 chestnut), used in brandy ageing, were
studied by GC–MS and the modification induced by the heat treatment, that occurs during the barrel making, was evaluated. Some
of these compounds are identified for the first time, namely the 4-hydroxy-2-butenoic acid lactone in oak and chestnut wood, and
2 + 3-methyl-1-butanol, benzaldehyde, acetovanillone, b-methyl-c-octalactone, guaiacol, 4-methylguaiacol, 4-propylguaiacol,
4-ethylguaiacol, eugenol, isoeugenol, 4-methylsyringol and 4-allyl-syringol in chestnut. Eugenol, cis-b-methyl-c–octalactone, furfural,
4-hydroxy-2-butenoic acid lactone, hexanoic acid and guaiacol seemed to be important compounds, which could help to control
the wood origin. The toasting process modified strongly the volatile composition of the different types of wood, particularly the
levels of furanic aldehydes (furfural, 5-methylfurfural, HMF), volatile phenols (syringol and 4-allyl-syringol), propanoic acid,
4-hydroxy-2-butenoic acid lactone and vanillin.
Ó 2005 Elsevier Ltd. All rights reserved.
Keywords: Volatiles; Oak; Chestnut; Toasting
1. Introduction
Journal of Food Engineering 76 (2006) 202–211
The ageing of brandy and other alcoholic beverages is
usually performed by its storage in oak barrels for many
years. During this maturation period, also known as
barrel-ageing, the beverage acquires interesting sensorial
characteristics, as a result of extraction and the degradation
of many compounds from the woodÕs matrix. Historically
several types of wood have been used, but the
most commonly used wood, which is also the most studied,
is oak wood, namely some European species
(Quercus robur and Quercus sessiliflora) and white oak
from America (Quercus alba).
*
Corresponding
261712426.
author. Tel.: +351 261712106; fax: +351
E-mail addresses: inia.evn.tec@oninet.pt, inia.evn.quim@oninet.pt
(I. Caldeira).
0260-8774/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jfoodeng.2005.05.008
www.elsevier.com/locate/jfoodeng
The process of barrel making, known as cooperage,
consists of several steps, including preparation of stave
wood, drying and seasoning of the wood, ‘‘raising’’ the
barrel, bending under heat and toasting, bevelling,
grooving and placing heads, hooping and checking
(Puech & Moutounet, 1993).
The volatile compounds extracted from the wood
during barrel-ageing are very important, because they
are related to some flavour properties of alcoholic beverage.
The accumulation of volatile oak compounds in
brandy during the maturation period depends on many
factors, particularly the quantity of volatile compounds
available and their precursors presented in the woodÕs
matrix. The amount of volatile oak compounds depend
on several factors, such as geographical origin, the species
of oak (Canas, Leandro, Spranger, & Belchior,
2000; Chatonnet & Dubourdieu, 1998; Marco,
Artajona, Larrechi, & Rius, 1994; Masson, Guichard,

Fournier, & Puech, 1995; Miller, Howell, Michaelis, &
Dickman, 1992; Mosedale & Savill, 1996; Nabeta,
Yonekubo, & MiYake, 1986; Sefton, Francis, Pocock,
& Williams, 1993), the seasoning of the staves (Chatonnet,
1995; Sefton et al., 1993) and the toasting of the
barrel (Artajona, 1991; Canas, 2003; Chatonnet, 1995;
Chatonnet, Boidron, & Pons, 1989; Dubois, 1989;
Maga, 1985; Nishimura, Onishi, Masuda, Koga, &
Matsuyama, 1983; Nomdedeu et al., 1988; Sarni, Moutounet,
Puech, & Rabier, 1990).
In spite of a substantial knowledge about volatile
composition of French and American oak wood, few
data are available for others woods, namely chestnut
and oak Portuguese woods (Borralho, 1994; Clímaco &
Borralho, 1996) and from a cooperage point of view
the first chestnut wood results were presented in preceding
works (Canas, Leandro, Spranger, & Belchior, 1998,
1999). In our previous work, it was found that the brandies
aged from chestnut barrels presented a good quality
(Belchior et al., 1998; Caldeira et al., 1998) and higher
levels of some phenolic compounds (Canas, Caldeira,
et al., 1998; Canas, Leandro, Spranger, & Belchior,
1999).
The aim of this study is to characterise Portuguese
chestnut and oak wood comparatively with French
and American oak wood, using volatile composition
and also to point out the modifications induced by the
heat treatment, made during the cooperage process.
2. Material and methods
2.1. Experimental design and wood sampling
A two factorial design (7 woods · 4 toasting levels · 2
replicates) was established and 56 wood samples were
taken.
The anatomical study (Carvalho, 1998) led to the
botanical identification of seven wood species: three
Portuguese oak wood, which were all Quercus pyrenaica
Willd. from three different sites in the north of Portugal
(CNE, CNF, CNG); two French oak wood, one from
Allier identified as Quercus sessiliflora Sallisb. (CFA)
and another from Limousin region identified as Quercus
robur L. (CFL); one American oak wood which was a
mixture of Quercus alba L./Quercus stellata Wangenh.
and Quercus lyrata Walt./Quercus bicolor Willd.(CAM)
and one Portuguese chestnut wood (CAST), from the
northern, identified as Castanea sativa Mill. From each
wood, six barrels were constructed, which were submitted
to heat treatment with 3 degrees of toasting: light
(QL), medium (QM) and strong (QF), with two replicates
of each. Before and after the toasting process of
the barrels, shaves were cut in order to get samples from
the wood. The two replicates of each wood, taken before
toasting, represent the fist level of toasting factor (Q0).
I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211 203
The toasting process was controlled by the cooper 1 ,
which is about 10 min (light toasting), 20 min (medium
toasting) and 25 min (strong toasting) of slow toasting
the barrel, over a fire of the respective wood offcuts.
2.2. Wood extraction
Hydroalcoholic wood extracts were obtained with
50 g of milled wood (Hammer-Mill–Wiley) macerated,
under rotary agitation for 180 min at 20 °C, with
1000 mL of an ethanol–water solution at 55% v/v adjusted
to pH 4.2 with hydrochloric acid, according to
conditions previously selected (Caldeira, Pereira,
Clímaco, Belchior, & Bruno de Sousa, 2004).
The hydroalcoholic wood extracts were filtered
through a glass microfibre filter (Whatman GF/C) in a
Büchner funnel.
2.3. Wood moisture
The wood powder moisture was determined in a
moisture analyser (Mettler LJ 16-Switzerland).
2.4. Analysis of volatile compounds
The isolation of the volatile compounds, from the
hydroalcoolic wood extracts, was done by liquid/liquid
extraction with three successive aliquots of dichloromethane,
and the analysis of the compounds by GC
and GC–MS, was carried out as described by Caldeira
(2004) and Caldeira et al. (2004), with some modifications
on the GC conditions: each concentrated extract
was injected in a Carlo Erba 6000 Vega series equipped
with a flame ionisation detector (250 °C) and with a silica
capillary column (DB-WAX–J&W: 30 m-lengh,
0.32 mm-internal diameter, 0.25 lm-film thickness); elution
was carried out with hydrogen as carrier gas
(1.4 mL min 1 ); temperature program: 3.5 °C min 1
from 45 °C (5-min isothermal) to 210 °C (30-min isothermal);
the injector was at 250 °C, and approximately
0.8 lL was injected with a split ratio of 1:15.
Quantification was carried out by the internal standard
method; the response factor of volatile compounds
to the internal standard was arbitrarily fixed at 1.0 and
the results were expressed as lg/g of dry wood.
2.4.1. Reagents
All solvents used were analytical grade purchased
from Merck (Darmstadt, Germany) and the dichloromethane
were bidistilled.
2.4.2. Reference compounds
Acetic acid was purchased from Riedel-de-Haen (Seelze,
Germany); 2-methyl-1-butanol, 3-methyl-1-butanol,
1 Tanoaria J. M. Gonçaves, Palaçoulo-Portugal.

204 I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211
2-octanol, furfural, benzaldehyde, propanoic acid, 5methyl-furfural,
4-hydroxy-2-butenoic acid lactone,
hexanoic acid, guaiacol, 2-phenylethanol, octanoic
acid, eugenol, 3,4-dimethylphenol, syringol, decanoic
acid, dodecanoic acid, 5-hydroxymethyl-2-furaldehyde
(HMF), 4-hydroxy-3-methoxy-benzaldehyde (vanillin)
were purchased from Fluka (Buchs, Switzerland);
cis,trans-b-methyl-c-octalactone, 4-propyl-guaiacol, isoeugenol,
4-methyl-syringol, 4-allyl-syringol, acetovanillone
were purchased from Aldrich (Steinheim,
Germany); 4-methyl-guaiacol, 4-ethylguaiacol were purchased
from TCI. All of them were used as standards
without further purification. Solutions were prepared
with ethanol/water (20:80 v/v).
2.5. Statistical analysis
Analysis of variance (ANOVA). The results of the
volatile compounds analysed from the 56 wood samples
were submitted to a two-way analysis of variance,
with wood origin (7 levels: CNE, CNF, CNG, CAST,
CFA, CFL, CAM) and toasting intensity (4 levels: without
toasting, Q0; light toasting, QL; medium toasting,
QM; strong toasting, QF) as permanent factors. Calculation
of the least significant difference (LSD) was applied,
for comparison of the different averages, of the
volatile compounds (Montgomery, 1991). All the calculations
were performed using Statgraphics-statistical
system/ vs 5.0.
Multivariate analysis. The results were also subjected
to the multivariate analysis (clustering, principal component
analysis). All the calculations were carried out
1
i.s.1
2
3
4
5
6
7
8 9
10
11
12+13
using NTSYS-pc package, version 1.7 (Rohlf, 1993)
and the StatisticaÕ98 edition.
3. Results and discussion
3.1. Volatile compounds identified
Among the several chromatographic peaks present in
the oak extracts, 26 compounds were identified (Fig. 1).
Many of the volatile compounds identified by GC and
GC–MS analysis on the aqueous alcoholic wood dichloromethane
extracts are recognised as being present in
untreated oak extracts and in heated oak extracts by
various authors (Artajona, 1991; Chatonnet et al.,
1989; Clímaco & Borralho, 1996; Dubois, 1989; Marco
et al., 1994; Marsal & Sarre, 1987; Masson et al., 1995;
Masuda & Nishimura, 1971; Mosedale & Savill, 1996;
Nabeta et al., 1986; Nishimura et al., 1983; Pérez-Coello,
Sanz, & Cabezudo, 1999; Sefton et al., 1993). However,
the 4-hydroxy-2-butenoic acid lactone was identified
for the first time in oak wood and chestnut wood. Alford
and Leffingwell (1998) also identified this lactone in
wood smoke. According to Yanagimoto, Lee, Ochi,
and Shibamoto (2002) this compound could result from
furfural oxidation. Considering the interesting sensorial
properties of the lactones (Brenna, Fuganti, & Serra,
2003) further research on this compound is intended.
In chestnut wood the compounds 2 + 3-methyl-1butanol,
benzaldehyde, acetovanillone, b-methyl-c-octalactone,
guaiacol, 4-methyl-guaiacol, 4-propyl-guaiacol,
4-ethyl-guaiacol, eugenol, isoeugenol, 4-methyl-syringol,
17
15
14 16
10 20 30 40 50 60 70
Time (min)
Fig. 1. GC chromatogram of a dichloromethane wood extract, from a barrel submitted to a high toasting degree. Peak identification: (1) 2-Methyl-1butanol
+ 3-methyl-1-butanol, i.s.1:2-octanol; (2) acetic acid; (3) furfural; (4) benzaldehyde; (5) propanoic acid; (6) 5-methyl-furfural; (7) 4-hydroxy-
2-butenolactone; (8) hexanoic acid; (9) guaiacol; (10) trans-b-methyl-c-octalactone; (11) 2-phenylethanol; (12) + (13) cis-b-methyl-c-octalactone +
4-methyl-guaiacol, (14) 4-ethylguaiacol; (15) octanoic acid; (16) 4-propyl-guaiacol; (17) eugenol, i.s.2:3,4-dimethylphenol, (18) syringol, (19) decanoic
acid; (20) isoeugenol; (21) 4-methyl-syringol; (22) dodecanoic acid; (23) 5-hydroxymethyl-2-furaldehyde (HMF); (24) 4-allyl-syringol; (25) 4-hydroxy-
3-methoxy-benzaldehyde (vanillin); (26) acetovanillone.
i.s.2
18
19
20
21
22
23
24
25
26

4-allyl-syringol were also identified for the first
time.
Some authors reported the presence of other phenols,
namely phenol, o-cresol, p-cresol, m-cresol, 4-ethylphenol
and methyleugenol (Chatonnet et al., 1989; Nabeta
et al., 1986; Nishimura et al., 1983) but these compounds
were not found in our wood extracts.
3.2. Effect of wood origin
The cooperage industry needs to have criteria for the
control of raw material. Thus, we decided first to compare
the 14 unheated wood samples (7 woods · 2 replicates),
in order to evaluate the possibility of
discriminating the different types of wood based on the
levels of volatile compounds, and after that, we compare
all the wood samples in order to evaluate if the wood
discriminating pattern is influenced by the toasting
process.
I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211 205
Table 1 includes the quantitative analysis of several
volatile compounds in the unheated woods and the
ANOVA results, whereas Table 2 presents the results
from the analysis of all the different types of wood
(unheated and heated woods).
The high standard deviation indicates the strong variability
of the contents of these compounds in the different
types of wood, which is in agreement with the results
of other authors (Canas et al., 2000; Chatonnet &
Dubourdieu, 1998; Masson et al., 1995; Mosedale &
Savill, 1996; Simon, Conde, Cadahia, & Garcia-Vallejo,
1996).
The ANOVA showed (Table 1) that wood origin had
a very highly significant effect on the quantity of cis-bmethyl-c-octalactone
and eugenol, a highly significant
effect in the levels of acetic acid, furfural, 4-hydroxy-2butenoic
acid lactone, hexanoic acid, trans-b-methyl-coctalactone
and vanillin, and a significant effect on the
levels of guaiacol.
Table 1
Contents of volatile compounds in aqueous alcoholic unheated wood extracts and wood origin effect (results expressed as lg per g of dry wood)
Wood origin effect CNE CNF CNG CAST CFA CFL CAM
Acetic acid ** x 12.22a 67.97d 50.65c 19.09ab 70.20d 13.67a 34.74bc
SD 5.16 0.58 9.61 11.19 6.87 0.54 5.29
Furfural ** x 1.94a 12.51b 4.64a 2.27a 13.63b 4.51a 9.78b
SD 0.67 3.27 0.06 0.81 3.32 1.47 0.28
5-Methyl-furfural n.s. x 0.00 0.28 0.00 0.25 0.77 0.28 0.63
SD 0.00 0.40 0.00 0.35 0.19 0.40 0.31
4-Hydroxy-2-butenoic acid lactone ** x 0.00a 1.27b 0.00a 0.27a 1.50b 0.00a 1.26b
SD 0.00 0.48 0.00 0.39 0.35 0.00 0.43
HMF n.s. x 1.67 2.40 2.70 0.91 0.98 0.26 0.84
SD 1.29 0.43 0.07 0.14 1.38 0.37 0.05
Propanoic acid n.s. x 0.00 0.82 0.36 0.21 0.89 0.00 0.36
SD 0.00 0.04 0.50 0.30 0.40 0.00 0.51
Hexanoic acid ** x 0.64a 8.35b 1.47a 1.16a 8.76b 1.06a 12.52b
SD 0.00 4.27 0.06 0.71 2.21 0.01 2.27
trans-b-Methyl-c-octalactone ** x 2.31bc 2.68bc 2.47bc 0.23a 1.93b 2.87c 2.73bc
SD 0.23 0.79 0.24 0.33 0.06 0.35 0.21
cis-b-Methyl-c-octalactone *** x 6.72a 7.15a 5.30a 0.34a 4.93a 7.18a 35.40b
SD 3.79 3.00 0.67 0.48 0.30 1.39 6.44
Octanoic acid n.s. x 0.75 3.24 2.15 1.41 5.64 1.04 3.92
SD 0.16 2.40 0.74 1.21 1.88 0.09 1.69
Decanoic acid n.s. x 1.60 0.51 2.40 1.42 1.55 1.51 0.87
SD 0.22 0.72 1.70 0.45 0.08 0.78 0.02
Dodecanoic acid n.s. x 2.03 1.56 3.82 0.88 1.01 3.86 1.92
SD 0.01 0.05 2.21 1.24 1.42 0.13 0.50
Guaiacol * x 0.42a 1.25b 0.32a 0.38a 1.19b 0.09a 1.48b
SD 0.25 0.45 0.45 0.26 0.35 0.13 0.02
Eugenol *** x 0.94a 2.69b 1.08a 0.71a 1.17a 1.01a 4.48c
SD 0.02 0.52 0.48 0.06 0.15 0.11 0.33
Syringol n.s. x 0.39 0.36 0.00 0.53 0.36 0.00 0.00
SD 0.56 0.51 0.00 0.21 0.51 0.00 0.00
4-Allyl-syringol n.s. x 1.07 0.45 1.40 1.53 0.33 0.66 2.00
SD 0.64 0.63 0.60 0.06 0.47 0.93 1.12
Vanillin ** x 4.78bc 4.78bc 5.50c 2.90ab 8.32d 1.21a 5.78c
SD 1.32 0.10 0.56 1.25 0.89 0.29 0.06
Acetovanillone n.s. x 1.89 0.00 0.00 1.28 0.44 0.00 0.91
SD 1.24 0.00 0.00 1.81 0.63 0.00 0.13
x, means of two values; SD, standard deviation; means followed by the same letter in a row are not significantly different at the 0.05*, 0.01** or
0.001*** level of significance; n.s. without significant difference.

206 I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211
Table 2
Contents of volatile compounds in aqueous alcoholic wood extracts (unheated and heated woods) and wood origin effect (results expressed as lg per
g of dry wood)
Compound Wood origin effect CNE CNF CNG CAST CFA CFL CAM
Acetic acid ** x 31.23a 63.46cd 77.26d 34.33a 52.16bc 45.67ab 42.51ab
SD 13.55 23.76 22.73 16.79 15.63 21.09 22.17
Furfural n.s. x 105.53 78.99 138.33 86.38 92.85 83.58 92.85
SD 157.07 56.70 140.92 113.73 50.96 45.81 80.32
5-Methyl-furfural n.s. x 10.40 9.63 16.80 11.04 10.70 14.14 15.39
SD 17.03 9.87 20.64 13.63 8.14 8.67 15.38
4-Hydroxy-2-butenoic acid lactone ** x 0.59a 1.05ab 1.84c 1.37bc 1.48bc 1.53bc 1.61c
SD 1.03 0.57 1.43 1.02 0.34 1.22 0.86
HMF ** x 13.15a 23.53bc 26.42c 16.60ab 13.22a 23.06bc 13.63a
SD 14.92 23.90 26.26 16.03 12.31 21.15 14.09
Propanoic acid * x 0.37a 0.44a 0.99b 0.40a 0.53a 0.67ab 0.57a
SD 0.63 0.39 0.58 0.33 0.40 0.54 0.53
Hexanoic acid ** x 1.21a 4.13b 3.43b 3.75b 4.95bc 1.55a 6.43c
SD 0.40 3.28 2.50 2.21 3.16 0.75 4.99
trans-b-Methyl-c-octalactone ** x 3.07bc 2.95bc 3.10bc 0.66a 1.60ab 5.63d 4.26cd
SD 0.88 0.94 1.93 0.31 0.95 3.07 1.04
cis-b-Methyl-c-octalactone + 4-methyl-guaiacol ** x 9.15bc 11.24c 8.80bc 0.88a 4.50ab 17.99d 46.59e
SD 4.54 6.93 4.71 0.72 2.38 13.06 9.43
Octanoic acid n.s. x 2.02 2.53 2.10 2.61 2.87 1.77 2.48
SD 1.83 2.49 0.81 1.24 2.07 1.14 1.47
Decanoic acid n.s. x 2.31 2.19 1.31 1.26 1.13 2.17 1.02
SD 0.80 3.39 1.00 0.40 0.49 1.06 0.31
Dodecanoic acid n.s. x 3.01 3.82 2.26 1.60 1.64 3.34 3.77
SD 2.12 4.56 1.34 0.77 1.10 1.81 2.13
Guaiacol ** x 1.59c 0.77a 1.00ab 0.93ab 1.07abc 0.62a 1.43bc
SD 0.25 0.45 0.45 0.26 0.35 0.13 0.02
Eugenol ** x 1.74ab 2.82d 1.86abc 2.11bcd 1.22a 2.65cd 4.55d
SD 0.86 1.34 1.11 1.14 0.36 1.73 0.47
Syringol n.s. x 0.86 1.38 1.37 0.91 0.79 2.05 1.44
SD 1.81 2.11 2.47 0.91 1.02 2.21 2.42
4-Allyl-syringol n.s. x 1.30 2.13 1.85 2.72 2.87 2.99 3.26
SD 1.25 1.61 1.79 1.09 4.34 2.13 1.67
Vanillin ** x 15.10a 18.86ab 21.13ab 24.70bc 24.17b 32.82c 22.56ab
SD 11.62 15.38 16.95 20.34 18.17 26.91 18.92
Acetovanillone * x 0.47a 1.93abc 1.59ab 2.60bc 1.60ab 3.63c 1.37ab
SD 1.05 4.02 2.56 2.01 1.25 2.71 1.08
x, means of eight values; SD, standard deviation; means followed by the same letter in a row are not significantly different at the 0.05*, 0.01** or
0.001*** level of significance; n.s. without significant difference.
When the analysis was performed with all the different
types of wood samples (Table 2) it was detected a
wood origin effect on the same variables, namely acetic
acid, 4-hydroxy-2-butenoic acid lactone, hexanoic acid,
trans-b-methyl-c-octalactone, cis-b-methyl-c-octalactone
+ 4-methyl-guaiacol, guaiacol, eugenol, and vanillin
with exception for the furfural, HMF, propanoic
acid and acetovanillone levels. However the results of
unheated wood discrimination, based on the majority
of analysed compounds, were quite different from those
obtained with all the different types of wood.
Only for the amounts of hexanoic acid, trans-b-methylc-octalactone,
cis-b-methyl-c-octalactone and eugenol,
the wood discrimination was similar on both analyses.
The two isomers of b-methyl-c-octalactone, which
have high sensory impact (Abbott, Puech, Bayonove,
& Baumes, 1995; Boidron, Chatonnet, & Pons, 1988),
allow to distinguish between French and American
oak extracts and their related aged beverages (Guichard,
Fournier, Masson, & Puech, 1995; Guymon & Crowell,
1972; Onishi, Guymon, & Crowell, 1977). In this work,
we found a significant effect of wood origin on trans and
cis isomer amounts in unheated woods (Table 1). Concerning
the Portuguese chestnut wood, it is remarkable
that it has a significant low level of these two isomers.
In fact, in a previous work on the chestnut volatile evaluation,
the b-methyl-c-octalactone isomers were not
found (Clímaco & Borralho, 1996). On the contrary to
other results (Masson et al., 1995; Mosedale & Savill,
1996) we found that CFL wood has higher amount of
trans isomer than CFA wood (Tables 1 and 2).
It was verified that cis-b-methyl-c-octalactone contents,
permits the formation of two groups, one constituted
by the CAM with the highest amounts of this
compound, and another with all the other types of wood.
These results are in agreement with other authors

(Chatonnet & Dubourdieu, 1998; Masson et al., 1995).
In the analysis of all the different types of wood (Table 2),
we found a similar wood discrimination based on
the contents of cis-b-methyl-c-octalactone + 4-methylguaiacol.
Concerning hexanoic acid, the variance analysis (Table
1) showed two different groups of wood, one constituted
by CFL, CNE, CAST and CNG with the lowest
contents and other formed by CNF, CFA and CAM
with higher content. Others authors also found this acid
in untoasted oak extracts (Boidron et al., 1988; Clímaco
& Borralho, 1996) and chestnut extracts (Clímaco &
Borralho, 1996). Similar wood discrimination could be
found in the ANOVA, concerning all the different types
of wood (Table 2).
Based on the eugenol amounts, three homogeneous
groups can be observed, by ordering them from the
poorest to the richest: CAST = CNE = CFL = CNG =
CFA < CNF < CAM. These results are similar to those
obtained by Pérez-Coello et al. (1999), but quite different
from the results observed by other authors (Chatonnet
& Dubourdieu, 1998; Doussot, Pardon, Dedier, &
De Jeso, 2000). The results obtained from the analysis
of all the different wood types are different, they confirm
that CAM is the richest wood in this compound, CFA is
a poorest wood and CNF is the richest, among the
Portuguese woods.
For both analyses (Tables 1 and 2), wood origin effect
on the levels of 5-methyl-furfural, octanoic acid, decanoic
acid, dodecanoic acid, syringol and 4-allyl-syringol
was not detected.
According to the results obtained, we have chosen the
compounds significantly affected by the wood origin, and
we have submitted these variables to a multidimensional
analysis (clustering and principal component analysis).
Fig. 2 presents the phenogram of distances for the
unheated wood types, which presented a cophonetic
1.67
1.25
0.83
Distance
0.42
CNE1
CNE2
CNG1
CNG2
CFL1
CFL2
CAST1
CAST2
CNF1
CNF2
CFA2
CFA1
CAM1
CAM2
0.00
Fig. 2. Phenogram of UPGMA clustering of unheated woods
according to volatile compounds levels. The initial matrix is composed
by 14 wood samples · 9 variables (1 and 2 indicate the replicate).
I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211 207
correlation coefficient of 0.88. The American oak wood
(CAM) forms an individual cluster, a second cluster
joins together Allier oak (CFA) and Portuguese oak
wood (CNF), a third cluster joins Portuguese oak woods
(CNE and CNG), Limousin oak wood (CFL) and chestnut
wood (CAST).
The principal component analysis for the 14 unheated
wood samples was performed (Fig. 3). The first three
principal components, which accounted 91% of the total
variance, separate the different types of wood, which is
in agreement with the clusters found in the phenogram.
The first component, which acounted 61% of total
variance, makes the major wood separation. It was possible
to observe a wood cluster (CAST, CNE, CNG and
CFL) with low levels of furfural, 4-hydroxy-2-butenolactone,
hexanoic acid and guaiacol in opposition to
the other woods analyzed (CFA, CNF and CAM) which
present high levels for the same variables. Chestnut is
not completely separated from other types of wood,
based on the low levels of the variables. The second
component seems to separate the CAM wood from
other woods due to itÕs higher levels of cis-b-methyl-coctalactone
and eugenol.
However, the cluster analysis of all the different types
of wood does not show clusters based on the wood origin
(Fig. 4). These results, in agreement with ANOVA
results, suggest that the toasting process affected the
wood discrimination. In fact, the principal component
analysis (Fig. 5) with all the different wood types shows
that the first component, which accounted 50% for the
total variance, divided the wood samples based on the
level of toasting. Only the second component divides
Comp. 2
(20%)
1.15
0.57
0.00
-0.57
CAST1
CAST2
CNE1
CFL1
CFL2
CNG2
CNG1
CNE2
CFA1
2
25
CNF1
CFA2
3
CNF2
7
CAM2
CAM1
-1.15
-1.15 -0.57 0.00
Comp. 1 (61%)
0.57 1.15
Fig. 3. Projection of unheated woods and variables in the space
defined by the first and second components. Variable identification: (2)
acetic acid; (3) furfural; (7) 4-hydroxy-2-butenoic acid lactone; (8)
hexanoic acid; (9) guaiacol; (10) trans-b-methyl-c-octalactone; (12) cisb-methyl-c-octalactone;
(17) eugenol; (25) vanillin.
10
12
17
9
8

208 I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211
1.93
1.52
American oak wood (CAM) from the others based on
the amounts of cis-b-methyl-c-octalactone + 4-methylguaiacol
and eugenol.
These results suggest that the analyses of certain volatile
compounds found in wood could help cooperage
industry to select or control wood quality, but it must
be done before the toasting process.
3.3. Toasting effect
1.11
Distance
CNEQ0
CFLQ0
CASTQ0
CNEQM
CNGQ0
CFAQL
CASTQL
CNFQM
CFLQL
CNFQ0
CFAQ0
CNGQL
CNGQM
CNFQL
CNEQF
CNFQF
CASTQM
CASTQF
CFAQF
CFAQM
CFLQM
CAMQM
CAMQL
CAMQ0
CNEQL
CNGQF
CFLQF
CAMQF
0.30
Fig. 4. Phenogram of UPGMA clustering of all the analysed woods
according to volatile compounds levels. The initial matrix was
composed by 28 woods · 15 variables.
Comp. 2
(13%)
0.48
0.13
-0.22
-0.57
Table 3 shows that the toasting degree has a very
highly significant effect on the quantity of compounds
0.71
CASTQ0
CASTQM
CNEQF
CNGQM
3
CNEQ0
CASTQF 23
CFAQM
CFAQL
CNGQ0
CNEQM
CNFQF
6
CFLQ0
CNFQM
25
26 2 18
CASTQL
5
CNGQL
CFAQ0 CNFQL
7
24
CFLQL
CNFQ0
CNEQL
8
CAMQL
CFAQF
CFLQM
17
CAMQM
CAMQF
CNGQF
12+13
-0.92
CAMQ0
-0.96 -0.31 0.33
Comp. 1 (50%)
0.98 1.62
9
10
CFLQF
Fig. 5. Projection of all woods and variables in the space defined by
the first and second components. (2) acetic acid; (3) furfural; (5)
propanoic acid; (6) 5-methylfurfural; (7) 4-hydroxy-2-butenolactone;
(8) hexanoic acid; (9) guaiacol; (10) trans-b-methyl-c-octalactone,
(12) + (13) cis-b-methyl-c-octalactone + 4-methylguaiacol; (17) eugenol;
(18) syringol; (23) HMF; (24) 4-allyl-syringol; (25) vanillin; (26)
acetovanillone.
found in the wood matrix, and for the majority of these
compounds, the evolution profile is similar: as toasting
intensity increases their concentrations rise (from Q0
until QF), reaching the highest concentrations in woods
strongly toasted (QF).
With toasting intensity increase and consequent temperature
raise (Chatonnet et al., 1989; Sarni, Rabier, &
Moutounet, 1990), most of the woods components suffer
physical, structural and chemical changes (Fengel & Wegener,
1989). The thermal degradation of wood polysaccharides
originates the formation of furanic derivatives,
namely furfural, 5-methylfurfural and 5-hydroxy-methylfurfural
and acetic acid. As summarised by Fengel
and Wegener (1989), HMF and 5-methylfurfural proceeds
from hexoses, that are the main constituents of
cellulose, and furfural derives from pentoses, the main
constituents of hemicelluloses. The acetic acid proceeds
from the acetyl groups present in the wood xylans, an
important group of wood hemicelluloses. For this
reason, it was observed a significant increase in the
amounts of these compounds (acetic acid, furfural,
5-methyl-furfural and 5-hydroxymetylfurfural) with the
increase of toasting level. It was possible to divide the
woods from different toasting levels based on the quantity
of these compounds.
The higher contents of furanic aldehydes was detected
in strongly toasted woods, which is in agreement
with several authors (Artajona, 1991; Nomdedeu et al.,
1988) but in disagreement with Chatonnet et al.
(1989), who found the higher levels in medium toasted
oaks.
The hemicelluloses are the most thermosensitive
wood polymer (Fengel & Wegener, 1989), they are preferentially
degraded during the toasting process, which
explains the high amount of furfural among the furanic
aldehydes (Table 3).
Concerning the amounts of 4-hydroxy-2-butenoic
acid lactone, their behaviour with toasting is similar to
the furanic aldehydes.
Under temperature effect wood lignins are also affected
(Fengel & Wegener, 1989), which could explain
the presence of many phenolic derivatives namely vanillin,
volatile phenols and acetovanillone.
In fact, it was observed that the toasting level had a
very highly significant effect on the quantity of eugenol,
syringol and 4-allyl-syringol found. Higher values were
found in strongly toasted woods, in disagreement with
other authors (Artajona, 1991; Chatonnet et al., 1989).
The results also show (Fig. 6) that the increase in the
amounts of syringyl-type compounds (syringol and
4-alylsyringol) are higher than the ones of guaiacyl-type
(guaiacol and eugenol) in oak wood, as described by
Chatonnet et al. (1989) and Sarni et al. (1990). This fact
could be explained by the dominance of syringil units in
the hardwood (oak and chestnut) lignins and also by
their higher thermal stability.

Table 3
Contents of volatile compounds in aqueous alcoholic wood extracts and toasting intensity effect (results expressed as lg per g of dry wood)
Compound Toasting effect Toasting intensity
Q0 QL QM QF
Acetic acid * x 38.36a 47.59ab 53.17b 58.94b
SD 24.43 27.22 20.70 20.22
Furfural *** x 7.04a 53.00a 103.77b 223.91c
SD 4.87 20.44 48.61 105.15
5-Methylfurfural *** x 0.32a 4.75a 13.86b 31.41c
SD 0.35 2.36 7.20 12.55
4-Hydroxy-2-butenoic acid lactone *** x 0.62a 0.78a 1.58b 2.44c
SD 0.71 0.67 0.77 0.84
5-Hydroxymethylfurfural *** x 1.40a 9.71b 21.48c 41.48d
SD 1.02 5.04 9.16 17.93
Guaiacol ** x 0.73a 1.09a 0.84a 1.57b
SD 0.58 1.18 0.38 0.76
Eugenol *** x 1.73a 2.39ab 2.49bc 3.07c
SD 1.34 1.25 1.44 1.39
Syringol *** x 0.24a 0.32a 0.80a 3.67b
SD 0.34 0.35 0.61 2.23
4-Allyl-syringol *** x 1.06a 1.83ab 2.75b 4.15c
SD 0.79 1.07 3.04 1.54
Vanillin *** x 4.75a 13.82b 25.87c 46.60d
SD 2.24 4.22 12.96 14.15
Acetovanillone * x 0.65a 2.37b 2.31b 2.21b
SD 0.95 2.95 1.97 2.59
Propanoic acid *** x 0.38a 0.30a 0.52a 1.08b
SD 0.42 0.38 0.36 0.55
Hexanoic acid * x 4.85b 3.42a 3.48ab 2.80a
SD 4.93 2.40 2.00 2.05
trans-b-Methyl-c-octalactone n.s. x 2.18 3.10 3.10 3.79
SD 0.92 2.11 2.15 2.97
cis-b-Methyl-c-octalactone + 4-methyl-guaiacol * x 9.57a 15.79b 14.92b 16.37b
SD 11.40 17.53 17.76 15.84
Octanoic acid n.s. x 2.59 2.92 1.92 1.92
SD 2.00 1.99 0.82 1.13
Decanoic acid n.s. x 1.41 2.07 1.31 1.72
SD 0.81 2.39 0.52 1.09
Dodecanoic acid n.s. x 2.15 4.02 2.41 2.54
SD 1.44 3.38 1.83 1.31
x, means of fourteen values; SD, standard deviation; means followed by the same letter in a row are not significantly different at the 0.05*, 0.01** or
0.001*** level of significance; n.s.: without significant difference.
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Q0 QL QM QF
Guaiacol/Syringol Eugenol/4-Allyl-syringol
Fig. 6. Effect of toasting level on the guaiacyl/syringyl ratio on the all
woods analysed.
Concerning the amounts of guaiacol, the toasting
level has a significant effect on this compound, as well
as the interaction wood origin · toasting level. The guaiacol
amount increases with toasting level in CAM and
I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211 209
CFL woods; on the other hand for CNG, CAST and
CFA the toasting had no effect and for the other woods
the behaviour are different. Further research is needed to
evaluate this question, but we hypothesize that two phenomenonÕs
occur simultaneously: formation of guaiacol
as result of thermal degradation of lignin and also itÕs
decrease due to its thermal degradation.
The vanillin amount increases with toasting level and
the higher levels are found in high toasted wood, as referred
by others authors (Artajona, 1991; Canas, 2003;
Nomdedeu et al., 1988) and in disagreement with
Chatonnet et al. (1989). It was also possible to discriminate
each level of toasting based on the amounts of this
compound.
Regarding acetovanillone, the toasting level has a significant
effect on this compound, as well as the interaction
wood origin · toasting level. In fact the toasting

210 I. Caldeira et al. / Journal of Food Engineering 76 (2006) 202–211
level had only effect on the contents of this compound
for CNF and CFL woods.
For the majority of the acids the toasting process
does not affect their contents, except for hexanoic and
propanoic acids. For the former it was found a decrease
with the increase in the toasting level and also it was detected
effect of interaction factors; so the toasting process
only affected the hexanoic levels of five types of
wood (CNF, CNG, CAST, CFA and CAM). Toasting
effect and interaction effect was also detected for propanoic
acid. For CNF, CAST and CFA the toasting level
did not affect the propanoic acid contents, although in
the other types of wood studied, higher toasting level increased
the quantity of this compound.
It can be also noted that the toasting level effect on
the amounts of cis-b-methyl-c-octalactone + 4-methylguaiacol
was significant, but for the trans-b-methyl-coctalactone
the toasting do not affect itÕs contents, which
disagree with the results obtained using French oak
wood by Chatonnet et al. (1989).
The principal component analysis (Fig. 5) shows that
the initial wood group division, made by the first component,
seems based on the toasting level, which increases
across the component. In fact the unheated
woods are located in the negative branch of this component,
in opposite to the strongly toasted woods, which
are located in positive branch of this component. Nevertheless
it seems that the division between the successive
toasting levels is not clear. This could be due to the
strong variability resulting from many uncontrolled
parameters during the heat treatment.
The variables, which influence most the first component,
are the furanic aldehydes (furfural, 5-methyl-furfural,
HMF), 4-hydroxy-2-butenoic acid lactone, vannilin,
propanoic acid and volatile phenols with a syringyl-type
structure, namely syringol and 4-allyl-syringol. The increase
in toasting level enhances the quantity of these
compounds in wood. These results could explain the
sensory significant differences found in the brandies
aged, in these barrels (Caldeira, Belchior, Clímaco, &
Bruno de Sousa, 2002).
4. Conclusions
This present work permitted the identification, for the
first time, of the 4-hydroxy-2-butenoic acid lactone in
oak and chestnut wood, moreover, also for the first
time, 2 + 3-methyl-1-butanol, benzaldehyde, acetovanillone,
b-methyl-c-octalactone, guaiacol, 4-methylguaiacol,
4-propylguaiacol, 4-ethylguaiacol, eugenol,
isoeugenol, 4-methylsyringol and 4-allyl-syringol were
identified in chestnut wood.
These results pointed out that the unheated wood discrimination
is possible based on certain volatile compounds
namely eugenol, cis-b-methyl-c-octalactone,
furfural, 4-hydroxy-2-butenolactone, hexanoic acid
and guaiacol. Nevertheless after the toasting process,
wood discrimination is weaker and it is only possible
to discriminate the American oak wood from the other
types of wood based on amounts of eugenol and cis-bmethyl-c-octalactone
present.
For the seven woods studied, including the Portuguese
chestnut, this work showed that the increase in
the level of toasting is related to the increase in the levels
of many compounds. The most affected were furanic
aldehydes (furfural, 5-methylfurfural, HMF), volatile
phenols (syringol and 4-allyl-syringol), propanoic acid,
4-hydroxy-2-butenolactone and vanillin.
Acknowledgements
The authors thank Madalena Miguel for technical
assistance, Sun Baoshan and Marlene Vaz for manuscript
revision and PAMAF-IED-2052 for the financial
support.
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