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EFFECT OF HEAT TREATMENT ON THE THERMAL AND CHEMICALMODIFICATIONS OF OAK AND CHESTNUT WOOD USED IN BRANDY AGEING

EFEITO DO TRATAMENTO TÉRMICO NAS MODIFICAÇÕES TÉRMICAS E QUÍMICAS DASMADEIRAS DE CARVALHO E DE CASTANHEIRO UTILIZADAS NO ENVELHECIMENTO DE

AGUARDENTES

S. Canas1, A.P. Belchior1, A. Falcão2, J.A. Gonçalves3, M. I. Spranger1, R. Bruno-de-Sousa4

1 Estação Vitivinícola Nacional, 2565-191 Dois Portos, Portugal2 Instituto Tecnológico Nuclear, 2686-953 Sacavém, Portugal3 Universidade de Trás-os-Montes e Alto Douro, 5001 Vila Real, Portugal4 Instituto Superior de Agronomia, Departamento de Química Agrícola e Ambiental, Tapada da Ajuda, 1349-017 Lisboa, Portugal

(Manuscrito recebido em 22.03.07 . Aceite para publicação em 07.05.07.)

SUMMARY

The effects of temperature and frequency of moistening during the first phase of the heat treatment (bending phase) on the simultaneousresponse of different kinds of wood (Portuguese chestnut, Rumanian and American oak wood) used in brandy ageing were studied. Theevolution of the wood temperature was measured by K thermocouple probes. The wood extractable compounds (phenolic acids, phenolicaldehydes, coumarins and furanic derivatives) were analysed by HPLC. The results showed that the thermal distribution along the thickness ofthe stave is influenced by the temperature and frequency of moistening, and also by the botanical species. It was verified that the bending phaseis of great importance for the barrel quality not only for its impact on the physical and mechanical properties of the wood but also for its effecton the wood chemical composition.

RESUMO

No presente trabalho são estudados os efeitos da temperatura de vergatura e da frequência do humedecimento durante a primeira fase dotratamento térmico (fase de vergatura) na resposta simultânea, do ponto de vista térmico e químico, de diferentes madeiras (castanheiroportuguês, carvalho americano e carvalho romeno) usadas no envelhecimento de aguardentes vínicas Para a determinação da temperatura damadeira recorreu-se a termopares do tipo K. Os compostos extraíveis da madeira (ácidos fenólicos, aldeídos fenólicos, cumarinas e aldeídosfurânicos) foram analisados por HPLC. Os resultados evidenciam que a distribuição da temperatura ao longo da espessura da aduela e acomposição química da madeira são influenciadas pela temperatura de vergatura e pela frequência do humedecimento, bem como pela espéciebotânica da madeira. É demonstrado que a fase de vergatura é de extrema importância para a qualidade da vasilha não apenas pelo seu impactonas propriedades físicas e mecânicas da madeira, mas por constituir também uma etapa determinante da composição química da mesma.

Keywords: oak; chestnut; cooperage; heat treatment; thermal and chemical modificationsPalavras chave: carvalho; castanheiro; tratamento térmico; modificações térmicas e químicas

INTRODUCTION

The wooden barrel quality, the chemicalcharacteristics of brandies, namely low molecularweight extractable compounds that are released fromwood to the distilled during the ageing process, andthe sensory properties of aged brandies are largelydetermined by heat treatment protocol (Puech et al.,1985; Artajona et al., 1991; Lavergne et al., 1991;Rabier and Moutounet, 1991; Canas et al., 1999;Belchior et al., 2001; Caldeira et al., 2002).

In European cooperage, the raised barrel is heatedover a fire of wood chips with various techniques ofspraying or swabbing with water to enable thebending of the staves to the concave shape of a barrel.Then, the barrel is placed again over the fire to heatthe inner surface to cause significant toasting in orderto modify the structure, the physical properties andthe chemical composition of wood, and to confer adistinct character to the brandies aged in it. In thelast twenty years several papers have focused on the

study of variables that are relevant for the heattreatment and their effects on the phenoliccomposition of French oak wood (Chatonnet andBoindron, 1989; Chatonnet, et al., 1989; Sarni et al.,1990; Sarni et al., 1991; Chatonnet, 1995) andAmerican oak wood (Hale et al., 1999; Matricardiand Waterhouse, 1999). More recently the study hasbeen extended to include Portuguese oak wood –Quercus pyrenaica Willd. (Canas et al., 2000a).However, the simultaneous response of differentkinds of wood, namely oak from differentgeographical origins and chestnut, to the sametemperature and moisture conditions of the heattreatment has never been analysed.

The results of our previous studies have demonstratedthat chestnut wood is suited for cooperage (Carva-lho, 1998) and has interesting properties for theageing of brandies (Canas et al., 1999; Belchior etal., 2001; Caldeira et al., 2002). On the other hand,oak wood originated from Eastern Europe (Rumania,

Ciência Téc. Vitiv. 22 (1) 5-14.2007

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Russia and Hungary) is increasingly used in theEuropean cooperage due to its ease of supply andlow price. Nevertheless, to our knowledge, itschemical composition has been investigated onlyoccasionally (Prida and Puech, 2006). Concerningthe heat treatment, some work has been done in orderto improve and rationalize the heat treatment onlywith French oak wood (Chatonnet et al., 1993;Chatonnet, 1999), reducing the variability associatedwith the empiric nature of the process (Towey andWaterhouse, 1996). Furthermore, there are only fewstudies published on the effects of moistening andheating of the wood, during the bending phase, onthe oak wood characteristics (Chatonnet andBoindron, 1989; Sarni et al., 1991; Boeglin et al.,1993; Matricardi and Waterhouse, 1999). Thus, thepurpose of this work is to study the effects oftemperature and moistening on the temperatureprofile and on the content of low molecular weightcompounds of the different kinds of wood, in orderto achieve a better control of the process and,consequently, to improve the quality of agedbrandies. Then the phase of bending the staves is

the three kinds of wood and three levels of moisteningfrequency: H0, H3 and H7 protocols under the samebending temperature - VA (150–155 ºC). Two barrels(replications) were used to test each moisteningprotocol. Experiment 2 was carried out to analyse theeffect of the bending temperature, using the threekinds of wood and two levels of bending temperature:VA and VB protocols under the same moisteningfrequency - H3 (three applications of water). Twobarrels (replications) were used to test eachtemperature protocol.

Wood samples

The heartwood staves of three different kinds ofwood were: Portuguese chestnut – Castanea sativaMill. from the North of Portugal (CT), Rumanianoak – Quercus robur L. from Lugoj (RO), andAmerican oak – Quercus alba L. fromPennsylvania (AO). The staves were seasoned inthe open air for three years, at a cooperage industry- JM Gonçalves - in Northern of Portugal. Eachbarrel integrated two staves of each kind of wood,placed opposite each other, as shown in Figure 1.

Fig. 1 - Wooden barrel scheme, according to (a) longitudinal and (b) cross sections, and positioning of the thermocouple probes along thestave thickness.

Esquema da vasilha de madeira, segundo os planos (a) longitudinal e (b) transversal, e posicionamento dos termopares na espessura daaduela.

characterized by monitoring, in a pilot-scale, thetemperature and the frequency of moistening appliedto barrels, integrating simultaneously staves ofPortuguese chestnut, American and Rumanian oakwoods.

MATERIALS AND METHODS

Experimental design

This study was based on two factorial experiments,involving two factors. Experiment 1 was performedto analyse the effect of the moistening frequency, using

Wood heating procedure

Concerning the fire, its temperature varied between850 ºC and 1000 ºC, and the wood offcuts used werefrom chestnut, Rumanian oak and American oak. Thewooden barrel was placed on a stand, 3 cm above thefloor level and heated over a fire of wood offcuts. Astainless steel cable was placed around the bottom ofthe barrel to gradually arch the staves and tighten themto obtain the shape of the barrel. Considering theresults of preliminary experiments and the results ofour previous study in the laboratory (Canas et al. ,2000a), it was decided that the bending phase shouldlast 25 minutes.

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In experiment 1, the protocols tested for themoistening process were: no moistening (H0);application of water after 5 minutes, 12 and 19minutes (H3); application of water after 5 minutes,7, 10, 13, 16, 19 and 22 minutes (H7). In eachapplication, the water (15 mL) was applied with asprayer in all directions, to wet the entire internalsurface of the barrel, done in conditionscomparable to those used industrially. Inexperiment 2, the temperature protocol used was:progressive increase of the wood temperature up to150–155 ºC (VA) or up to 120-125 ºC (VB). Aportion of each stave was not heat treated and keptas control group (V0). The temperature wasmeasured with centrally-placed K thermocoupleprobes (nickel/chromium and nickel/aluminum),which were put inside the six staves at 0.1 cm depth(m1) and 0.6 cm depth (m6) (Figure 1).The temperature was recorded by a data acquisitionsystem CR10X with a channel multiplication systemAM 416 relay multiplexer (Campbell Scientific,Leicestershire, UK). The measurements wereperformed with a frequency of 1 Hz (one measurementper second), and the means were recorded in periodsof 1 minute.

Wood extraction

After the heat treatment the wood chips of the centralpart (4 cm long, 4.6 cm width and 0.2 cm thicknessfrom inside) of each stave were obtained by planingand then they were gathered and grounded in ahammer-mill (Wiley, USA). Hydroalcoholic woodextracts were obtained with 50 g of milled woodmacerated under rotary agitation for 180 min at 20ºC, with 1000 mL of an ethanol-water solution at 55%v/v adjusted to pH 4.2 with hydrochloric acid(Caldeira et al. , 2004). The hydroalcoholic woodextracts were filtered through a glass microfibre filter(Whatman GF/C, UK) in a Büchner funnel.

HPLC analysis

Samples of wood extracts were added with an internalstandard (4-hydroxybenzaldehyde, 20 mg/L), filteredthrough 0.45 μm membrane (Titan) and analyzed bydirect injection of 20 μl. Chromatography wasperformed as described by Canas et al. (2003).

Chemicals

Ellagic acid dihydrate, gallic acid monohydrate,vanillic acid, syringic acid, ferulic acid, vanillin, 5-hydroxymethylfurfural, 5-methyl-furfural, furfural,scopoletin, and umbelliferone were from Fluka(Buchs, Switzerland).; syringaldehyde,coniferaldehyde, sinapaldehyde and 4-hydroxybenzaldehyde were from Aldrich (Steinheim,Germany). All of them were used as standards withoutfurther purification. The solutions were prepared withethanol/water (55:45 v/v) and were prepared fresh

prior to use.

All solvents used were HPLC gradient gradepurchased from Merck (Darmstadt, Germany).

Statistical analysis

The treatment of the data consisted in regressionanalysis and two-way analysis of variance that wereperformed using Statistica vs ’98 edition (Statsoft Inc.,Tulsa, USA).

RESULTS AND DISCUSSION

Effect of moistening on the thermal distributionalong the thickness of the stave

In Figure 2, for each kind of wood and each frequencyof moistening, the curves show the evolution of

Fig. 2 - Effect of moistening on the evolution of wood temperaturealong the thickness of the stave. The arrows point the time formoistening.Efeito do humedecimento na evolução da temperatura da madeiraao longo da espessura da aduela. As setas indicam os momentosde humedecimento.

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average temperatures at m1 and m6 (means of thetemperatures measured in two barrels).

The analysis of the curves shows that the timedependence on the temperature observed in differentpositions of the stave is similar to that observed inour previous study (Canas et al., 2000a). Thetemperatures belong to the endothermic phase ofwood. Furthermore, the assessment of the moisteningfrequency effect on the evolution of the temperaturein each kind of wood was firstly based on a regressionanalysis for modelling the curves. As regards to allthe studied curves, logarithmic regression [y= a +bLn(x)] is the best model for establishing arelationship between the wood temperature and thetime, based on the following statistical criteria: thecorrelation coefficient is higher than 0.95 (highpercentage of variance is explained by the regression)and the residual variance due to the adjustment error(lack-of-fit) is not significant. Calculations werecarried out by the least-squares method (analysis ofvariance with statistical F-test, including evaluationof the model lack-of-fit). The results obtained forslope, intercept, standard deviations of the slope andintercept, and correlation coefficient are resented inTable I.

of Q. alba. In oak woods there is only significantdecrease of the temperature at m1 between H0 andH7, and between H3 and H7. So, temperaturedecrease at m1 caused by H3 is higher in chestnutwood than in oak wood. This fact could be explainedby the difference in permeability of the different kindsof wood, higher in chestnut, whose porous structure(width of growth rings, proportion of early woodvessels and fibres) poses lower resistance to waterdiffusion through the wood (Feuillat and Keller, 1997;Carvalho, 1998). It is also shown that, for all kinds ofwood, the decrease of temperatures observed atposition m6 is only significant from H3 to H7,indicating that seven applications of water is the mosteffective protocol to lower the wood temperature inthe deeper portion of the 0.6 cm layer. On the otherhand, the frequency of moistening produces less effecton the temperature at m6 than at positions closer tothe inner surface. Concerning all moisteningprotocols, and for chestnut and American oak woods,the temperature observed at position m1 issignificantly higher than the temperature observed atposition m6. The temperature difference between m1and m6 with the H0 moistening protocol is higher inchestnut than in the other kinds of wood tested. This

Secondly, a student’s t-test at the significance levelα=0.05 was used to perform the comparison of theintercepts and the slopes of the different curves(Bouvier, 1994) - Table II. The results shown in Figure2 and those obtained in all comparisons (Table II)pointed to the continuous and significant decrease ofthe temperature at m1 in chestnut wood caused bythe increase of the moistening frequency. Matricardiand Waterhouse (1999) reported a similar behavior

could derive from the lower thermal conductivity ofthe former, probably associated with its higherporosity. However, the temperature differencebetween m1 and m6 with the H3 moistening protocolis lower in chestnut wood than in oak woods. Thedifferent behavior of chestnut in the case of H3 couldalso be justified by the difference in porosity. Thematerial with higher porosity presents higher waterabsorption and the absorbed water can improve the

TABLE I

Parameters of the wood temperature curves relative to different moistening protocolsParâmetros das curvas de temperatura das madeiras relativas aos diferentes protocolos de humedecimento

aintercept; bstandard deviation of the intercept; cslope; dstandard deviation of the slope; ecorrelationcoefficient; m1 - temperature measured at 0.1 cm depth; m6 - temperature measured at 0.6 cm depth; H0 -no moistening; H3 – three applications of water; H7 – seven applications of water.

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conduction properties of the system. With the H7protocol, the temperature differences between m1 andm6 in the different kinds of wood are small.

Effect of moistening on the content of lowmolecular weight compounds of the wood

The analysis of variance reveals that moistening only

affects significantly the content of syringic acid andconiferaldehyde (Table III). Two different responsesto the moistening are identified: syringic acidincreases with H3 and decreases with H7 indicatingthat its synthesis is favoured only by a certain quantityof water, while coniferaldehyde presents the oppositebehaviour, which demonstrates that three applications

TABLE III

Average concentration of low molecular weight compounds in wood extracts under moistening effect(mg/L, except for coumarins, which are in μg/L)

Concentração media dos compostos de massa molecular baixa dos extractos de madeira sob efeito dohumedecimento (mg/L, excepto cumarinas, em μg/L)

H0 - no moistening; H3 – three applications of water; H7 – seven applications of water.a5-Hydroxymethylfurfural; bFurfural; c5-Methylfurfural; dEllagic acid; eGallic acid; fVanillic acid; gSyringic acid; hFerulic acid; iVanillin;jSyringaldehyde; kConiferaldehyde; lSinapaldehyde; mUmbelliferone; nScopoletin.Means followed by the same letter in a column are not significantly different at the 0.05* or 0.01** level of significance; RSD – relativestandard deviation (minimum value –maximum value); ns – without significant difference.

TABLE II

Comparison of the wood temperature curves using the student’s t-test (moistening effect)Comparação das curvas de temperatura das madeiras através do teste t de student (efeito do humedecimento)

m1 - temperature measured at 0.1 cm depth; m6 - temperature measured at 0.6 cm depth; H0 -no moistening; H3 – three applications of water; H7 – seven applications of water.(*) indicates a significant difference between texperimental and ttabulated; ttab (98; 0.05)=1.9873

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of water are not sufficient to control the rise of thewood temperature in order to avoid the degradationof this compound formed from lignin. Therefore, theresults show the important role of the water duringthe bending phase, not only for the alteration of fibresplasticity and the control of the wood temperature,but also as a reagent on the transformation of woodpolymers (Lapierre et al. , 1986; Matricardi andWaterhouse, 1999) and their derivatives, althoughwith a differentiated action. The absence of effect onthe majority of the analysed compounds could beexplained by the great variability associated with thebending operation, expressed by the relative standarddeviation. Even so, in the essayed conditions, the H3protocol presents some advantages, due to its positive

interaction between moistening and wood botanicalspecies.

Effect of bending temperature on the thermaldistribution along the thickness of the stave

In Figure 3, for each kind of wood and each bendingtemperature, the curves display the evolution ofaverage temperatures at m1 and m6 (means of thetemperatures measured in two barrels).

The assessment of the bending temperature effect onthe evolution of the temperature in each kind of woodwas also based on a regression analysis. For all of thestudied curves, logarithmic regression [y= a +bLn(x)]is the best model for establishing a relationship

Fig. 3 - Effect of bending temperature on the evolution of woodtemperature along the thickness of the stave. The arrows point the

time for moistening.Efeito da temperatura de vergatura na evolução da temperatura da

madeira ao longo da espessura da aduela. As setas indicam osmomentos de humedecimento.

influence on the content of some importantcompounds for the brandy overall quality anddifferentiation, namely furfural, 5-methylfurfural(Canas et al., 2003; Caldeira, 2004) and ellagic acid(Goldberg et al., 1999; Duriez et al., 2001; Canas etal., 2003). The H7 protocol seems to originate moreuniform temperature on the wood layer with athickness of 0.6 cm starting from the inside out, butwithin a range that should not be sufficient to promotethe required chemical alterations. Despite the verysignificant effect of the botanical species on thecontent of some compounds, there is no significant

between the wood temperature and the time, basedon the statistical criteria referred above.The results obtained for slope, intercept, standarddeviations of the slope and intercept, and correlationcoefficient are presented in Table IV.

The results obtained by the student’s t-test at thesignificance level α=0.05 were presented in Table V.The results shown in Figure 3 and those of Student’st-test (Table V) demonstrate that the increase of thebending temperature causes a significant increase ofthe temperature at m1 in oak wood (American andRumanian). Chestnut wood responds differently to

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bending temperature, being its temperature at m1 lessdependent on the fire intensity. As reported previously,the response to the fire intensity depends on theanatomical and structural characteristics of the wood(Feuillat and Keller, 1997), as well as on the amountof biopolymers and extractable compounds (Fengeland Wegener, 1989) present.

Regarding the temperatures observed at position m6,there is a significant increase between VB and VA inall kinds of wood, being the highest differenceobserved in chestnut wood. As for all temperatureprotocols, the temperature observed at position m1 issignificantly higher than the temperature observed atposition m6 in American oak. In Rumanian oak thetemperature difference between m1 and m6 is onlysignificant with VA protocol. In chestnut wood thedifferences are not significant. Besides, the differencein temperature between m1 and m6 with the VAprotocol is higher in Rumanian oak and lower inchestnut wood (Figure 3 and Table V). The VB

TABLE IV

Parameters of the wood temperature curves relative to different bending temperature protocolsParâmetros das curvas de temperatura das madeiras relativas aos diferentes protocolos de temperatura de vergatura

aintercept; bstandard deviation of the intercept; cslope; dstandard deviation of the slope; ecorrelationcoefficient; m1 - temperature measured at 0.1 cm depth; m6 - temperature measured at 0.6 cm depth; VA -progressive increase of the wood temperature up to 150–155 ºC; VB - progressive increase of the woodtemperature up to 120-125 ºC.

TABLE V

Comparison of the wood temperature curves using the student’s t-test (bending temperature effect)Comparação das curvas de temperatura das madeiras através do teste t de student (efeito da temperatura de vergatura)

m1 - temperature measured at 0.1 cm depth; m6 - temperature measured at 0.6 cm depth; VA - progressive increase of the woodtemperature up to 150–155 ºC; VB - progressive increase of the wood temperature up to 120-125 ºC.(*) – indicates a significant difference between texperimental and ttabulated; ttab (98; 0.05)=1.9873

protocol permits higher uniformity of the temperaturealong the thickness of the stave, especially in chestnutand Rumanian oak.

Effect of bending temperature on the content oflow molecular weight compounds of the wood

The bending temperature has a great influence on thecontent of low molecular weight extractablecompounds analysed (Table VI). The total contentincreases significantly with the lowest bendingtemperature (VB - temperature up to 120–125 ºC)and decreases with the rising of the bendingtemperature (VA - temperature up to 150–155 ºC), asa result of the individual effects.

Individually, similar behavior was observed on HMF,sinapaldehyde, and especially coniferaldehyde, whichhad a very significant decrease at VA. These resultsindicate that large amounts of these compounds wereformed at 120-125 ºC and were volatilized attemperatures over than 150-155 ºC. The increase of

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TABLE VI

Average concentration of low molecular weight compounds in wood extracts under bending temperature effect (mg/L, except for coumarins,which are in μg/L)

Concentração media dos compostos de massa molecular baixa dos extractos de Madeira sob efeito da temperatura de vergatura (mg/L,excepto cumarinas, em μg/L)

V0 – control group; VA - progressive increase of the wood temperature up to 150–155 ºC; VB - progressive increase of the wood temperatureup to 120-125 ºC.a5-Hydroxymethylfurfural; bFurfural; c5-Methylfurfural; dEllagic acid; eGallic acid; fVanillic acid; gSyringic acid; hFerulic acid; iVanillin;jSyringaldehyde; kConiferaldehyde; lSinapaldehyde; mUmbelliferone; nScopoletin.Means followed by the same letter in a column are not significantly different at the 0.05* or 0.01** level of significance; RSD – relativestandard deviation (minimum value –maximum value); ns – without significant difference; nd – not detected.

HMF under lower temperature effect contradicts theconclusions of Sarni et al. (1991) and suggests thatthis compound proceeds from the hexoses of somepolysaccharides of the wood, other than cellulose. Thedecrease of coniferaldehyde at VA leads us to questionthe thermal resistance of this aldehyde to temperaturehigher than 150 ºC reported by Sarni et al. (1991),and to assume its dependence on other bendingconditions. It is interesting to point out thesynchronism between the evolution of vanillin andconiferaldehyde (its main precursor), i.e., they presentopposite behaviours along with the raise of bendingtemperature. The concentrations of gallic acid, ferulicacid and vanillic acid decrease with bendingtemperature intensity, reflecting their low thermalresistance. As for the first two compounds, there is asignificant interaction between the temperature andthe wood botanical species. The bending temperaturefavoured the formation of ellagic acid,syringaldehyde, umbelliferone, furfural and 5-methylfurfural, mainly between V0 and VB. Theabsence of significant difference of ellagic acidcontent between VA and VB could indicate low effectof this range of temperatures on the hydrolyzabletannins degradation, since this compound presentshigh fusion point (> 450 ºC). Under bending effect,the ellagic acid became the most abundant compoundof the wood and gallic acid became less important,which could derive from higher degradation ofelagitannins (Rabier and Moutounet, 1991;Chatonnet, 1995) than from gallotannins (Canas etal. , 2004) and the thermal sensitivity of gallic acid(Rabier and Moutounet, 1991). The syringaldehydeis produced by lignin degradation and/or by oxidation

of sinapaldehyde, presenting high thermal stability(Sarni et al., 1991). The umbelliferone seems to havehigher thermal resistance than scopoletin. Thecontinuous increase of furfural is a consequence of ahigher degradation of hemicelluloses than thedegradation of this furanic derivative at temperaturelower than 165 ºC (Sarni et al., 1991; Chatonnet etal., 1989; Boeglin et al., 1993). Syringic acid has asignificant decrease at VB and a slight increase atVA, along with the alteration of syringaldehyde, whichis its main precursor (Puech et al. , 1984). Theevolution of this phenolic acid depends significantlyon the wood botanical species. The wood botanicalspecies have also a very significant influence on thetotal content of phenolic acids and vanillin, whichpresent the highest values in chestnut and the lowestin American oak, as already observed in non-toastedwoods (Canas et al. , 2000b). The ellagic acidconcentration allows differentiating all of the studiedwoods, which explains the very significant interactionbetween the bending temperature and the botanicalspecies. The lower concentration of coniferaldehydein chestnut than in oak woods is also a prevailingcharacteristic of the non-toasted woods (Canas et al.,2000b). American oak wood presents the highest levelof scopoletin and the chestnut wood presents thelowest one, as observed in non-toasted woods (Canaset al., 2000b). So, the extreme abundance ofscopoletin in American oak, largely noticed in theliterature as a phenolic marker of this wood, is notsignificantly affected by the first phase of the heattreatment of the wood. The differences in the amountsof lignin derivatives between the different kinds ofwood could derive from the anatomical and structural

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characteristics of each wood (Feuillat and Keller,1997) and/or from the wood chemical specificities(Fengel and Wegener, 1989; Canas et al., 2000b; Pridaand Puech, 2006), namely the contents of solubletannins, gallic acid and ellagic acid that can determinetheir response to bending temperature, as well as thepermeability and the delignification process of thewood (Puech and Sarni, 1990).

CONCLUSIONS

This study provides, for the first time, specificinformation about the simultaneous thermal andchemical modifications of some Portuguese chestnut,American and Rumanian oak wood caused by thebending conditions during the barrel cooperage. Inthe essayed conditions, moistening frequency,bending temperature and kind of wood were shownto affect the time evolution profiles of the temperatureat different positions of the staves. Concerning thethermal effect, from the tested protocols, threeapplications of water are the most appropriate forthe chestnut wood studied, while seven applicationsof water are the most suitable for the oak woodsanalysed. From the chemical point of view threeapplications of water are preferable in the essayedconditions. Regarding the temperature, it is preferableto use lower temperatures (120-125 ºC) during thebending phase in order to obtain higher uniformityof the temperature along the thickness of the staveand the most positive chemical effect. Bothmoistening and heating play important roles in thephysical and chemical modifications of the woodduring the bending phase of the heat treatment. Asfor the latter, alteration induced in the hemicellulosesand lignin derivatives are relevant. So, the bendingphase is of great importance for the barrel qualitynot only for its impact on the physical and mechanicalproperties of the wood but also as a determinant stepon the wood chemical composition during the heattreatment.

ACKNOWLEDGEMENTS

The authors thank Cristina Matos for manuscriptrevision and PIDDAC 709/99 and PARLE (ProjectA) for the financial support.

REFERENCESArtajona J., Barbero E., Llobet M., Marco J., Parente F., 1991.Influence du “bousinage” de la barrique sur les qualitésorganoleptiques des brandies vieillis en fûts de chêne. In: Leseaux-de-vie traditionnelles d’origine viticole. 197-205. Bertrand,A. (ed.), Lavoisier - TEC & DOC, Paris.

Belchior A.P., Caldeira I., Costa S., Tralhão G., Ferrão A., MateusA.M., Carvalho E., 2001. Evolução das características fisico-químicas e organolépticas de aguardentes Lourinhã ao longo decinco anos de envelhecimento em madeira de carvalho e decastanheiro. Ciência e Téc. Vitiv., 16, 81-94.

Boeglin N., Kuzara S., Duchanois G., Masson D., 1993. Étude duchêne de tonnellerie: perméabilité et cintrage. Rev. Fr. Oenol.,144, 35-40.

Bouvier J.C., 1994. Guide d’évaluation et de validation d’uneméthode d’analyse chimique. INRA, Narbonne.

Caldeira I., 2004. The aroma of wine brandies aged in wood.Cooperage technology relevance. 238 p. Ph D Thesis, InstitutoSuperior de agronomia, Universidade Técnica de Lisboa.

Caldeira I., Belchior A.P., Clímaco M.C., Bruno-de-Sousa R.,2002. Aroma profiles of Portuguese brandies aged in chestnutand oak woods. Anal. Chim. Acta, 458, 55-62.

Caldeira I., Pereira R., Clímaco M.C., Belchior A.P., Bruno-de-Sousa R., 2004. Improved method for extraction of aromacompounds in aged brandies and aqueous alcoholic wood extractsusing ultrasound. Anal. Chim. Acta, 513, 125-134.

Canas S., Belchior A.P., Spranger M.I., Bruno-de-Sousa R., 2003.High-performance liquid chromatography method for analysis ofphenolic acids, phenolic aldehydes and furanic derivatives inbrandies. Development and validation. J. Sep. Sci., 26, 496-502.

Canas S., Grazina N., Spranger M.I., Belchior A.P., 2000a.Modelisation of heat treatment of Portuguese oak wood (Quercuspyrenaica Willd.). Analysis of the behaviour of low molecularweight phenolic compounds. Ciência e Téc. Vitiv., 15, 75-94.

Canas S., Leandro M.C., Spranger M.I, Belchior A.P., 1999. Lowmolecular weight organic compounds of chestnut wood (Castaneasativa L.) and corresponding aged brandies. J. Agric. Food Chem.,47, 5023-5030.

Canas S., Leandro M.C., Spranger M.I., Belchior A.P., 2000b.Influence of botanical species and geographical origin on thecontent of low molecular weight phenolic compounds of woodsused in Portuguese cooperage. Holzforschung, 54, 255-261.

Canas S., Spranger M.I., Belchior A.P., Bruno-de-Sousa R., 2004.Isolation and identification by LC-ESI-MS of hydrolyzable tanninsfrom Quercus pyrenaica Willd. and Castanea sativa Mill.heartwoods. In: Proceedings of the 4th Tannin Conference. 4.Philadelphia.

Carvalho A., 1998. Identificação anatómica e caracterização físicae mecânica das madeiras utilizadas no fabrico de quartolas paraprodução de aguardentes velhas de qualidade - denominaçãoLourinhã. Ciência e Téc. Vitiv. , 13, 71-105.

Chatonnet P., 1995. Influence des procédés de tonnellerie et desconditions d’élevage sur la composition et la qualité des vinsélévés en fûts de chêne. 268 p. Thèse doctorat, Université deBordeaux II. Institut d’Oenologie.

Chatonnet P., 1999. Discrimination and control of toastingintensity and quality of oak wood barrels. Am. J. Enol. Vit., 50,479-494.

Chatonnet P., Boindron J.N., 1989. Incidence du traitementthermique du bois de chêne sur sa composition chimique. 1erepartie: Définition des paramètres thermiques de la chauffe desfûts en tonnellerie. Conn. Vigne Vin, 23, 77-87.

Chatonnet P., Boidron J.N., Dubourdieu D., 1993. Maîtrise de lachauffe de brûlage en tonnellerie. Application à la vinification età l’élevage des vins en barriques. Rev. Fr. Oenol., 144, 41-53.

Chatonnet P., Boindron J.N., Pons M., 1989. Incidence dutraitement thermique du bois de chêne sur sa compositionchimique. 2e partie: Évolution de certains composés en fonctionde l’intensité de brûlage. Définition des paramètres thermiquesde la chauffe des fûts en tonnellerie. Conn. Vigne Vin, 23, 223-250.

Duriez P., Cren C., Luc G., Fruchart J.C., Rolando CH., TeissierE., 2001. Ingestion of cognac significantly increases plasmaphenolic and ellagic acid concentrations and plasma antioxidantcapacity in humans. In: Proceedings of 26th World Congress -Section Wine and health. 358-369. Adelaide.

Fengel D., Wegner G., 1989. Wood - Chemistry, Ultrastructure,

14

Reactions. 612 p. Walter de Gruyter, Berlin.

Feuillat F., Keller R., 1997. Variability of oak wood (Quercusrobur L., Quercus petraea Liebl.). Anatomy relating to caskproperties. Am. J. Enol. Vit., 48, 502-508.

Goldberg D.M., Hoffman B., Yang J., Soleas G.J., 1999. Phenolicconstituents, furans, and total antioxidant status of distilled spirits.J. Agric. Food Chem., 47, 3978-3985.

Hale M.D., McCafferty K., Larmie E., Newton J., Swan J.S., 1999.The influence of oak seasoning and toasting parameters on thecomposition and quality of wine. Am. J. Enol. Vit. , 50, 495-502.

Lapierre C., Monties B., Vassal-Gonthier A., Dworkin A., 1986.Differential calorimetric study of pine and poplar lignins between300 and 525 K. J. Appl. Pol. Sci., 32, 4561-4572.

Lavergne J., Olivier J., Thomas Y., Raffier C., Courvoisier S.A.,1991. Origine géographique des grumes - “bousinage” et gestiondes fûts neufs - incidences sur la composition des cognacs,. In:Les eaux-de-vie traditionnelles d’origine viticole. 206-212.Bertrand, A. (ed.), Lavoisier - TEC & DOC, Paris.

Matricardi L., Waterhouse A.L., 1999. Influence of toastingtechnique on color and ellagitannins of oak wood in barrel making.Am. J. Enol. Vit., 50, 519-526.

Prida A., Puech J.L., 2006. Influence of geographical origin andbotanical species on the content of extractives in American,French, and East European oak woods. J. Agric. Food Chem., 54,8115-8126.

Puech J.L., Jouret C., Goffinet B., 1985. Évolution des composésphénoliques du bois de chêne au cours du vieillissement del’armagnac. Sci. Alim., 5, 379-392.

Puech J.-L., Leauté R., Clot G., Momdedeu L, Mondies H., 1984.Évolution de divers constituants volatils et phénoliques des eaux-de-vie de cognac au cours de leur vieillissement. Sci. Alim., 4,65-80.

Puech J.-L., Sarni F., 1990. Delignification of oak wood with anethanol-water solution in a flow through reactor. Holzforschung,44, 367-371.

Rabier Ph., Moutounet M., 1991. Evolution d’extractibles de boisde chêne dans une eau-de-vie de vin. Incidence duthermotraitement des barriques. In: Les eaux-de-vie traditionnellesd’origine viticole. 220-230. Bertrand, A. (ed.), Lavoisier - TEC& DOC, Paris.

Sarni F., Moutounet M., Puech J.L., 1991. Composés phénoliquesextractibles de copeaux de bois de chêne. In Les eaux-de-vietraditionnelles d’origine viticole. In: Les eaux-de-vietraditionnelles d’origine viticole. 231-239. Bertrand, A. (ed.),Lavoisier - TEC & DOC, Paris.

Sarni F., Rabier Ph., Moutounet M., 1990. Fabrication desbarriques et thermotraitements: relevé des températures. Rev. Fr.Oenol., 123, 53-58.

Towey J.P., Waterhouse A.L., 1996. Barrel-to-barrel variation ofvolatile oak extractives in barrel-fermented chardonnay. Am. J.Enol. Vit. , 47, 17-20.