5 EFFECT OF HEAT TREATMENT ON THE THERMAL AND CHEMICAL MODIFICATIONS OF OAK AND CHESTNUT WOOD USED IN BRANDY AGEING EFEITO DO TRATAMENTO TÉRMICO NAS MODIFICAÇÕES TÉRMICAS E QUÍMICAS DAS MADEIRAS DE CARVALHO E DE CASTANHEIRO UTILIZADAS NO ENVELHECIMENTO DE AGUARDENTES S. Canas 1 , A.P. Belchior 1 , A. Falcão 2 , J.A. Gonçalves 3 , M. I. Spranger 1 , R. Bruno-de-Sousa 4 1 Estação Vitivinícola Nacional, 2565-191 Dois Portos, Portugal 2 Instituto Tecnológico Nuclear, 2686-953 Sacavém, Portugal 3 Universidade de Trás-os-Montes e Alto Douro, 5001 Vila Real, Portugal 4 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 simultaneous response of different kinds of wood (Portuguese chestnut, Rumanian and American oak wood) used in brandy ageing were studied. The evolution of the wood temperature was measured by K thermocouple probes. The wood extractable compounds (phenolic acids, phenolic aldehydes, coumarins and furanic derivatives) were analysed by HPLC. The results showed that the thermal distribution along the thickness of the stave is influenced by the temperature and frequency of moistening, and also by the botanical species. It was verified that the bending phase is 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 effect on 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 do tratamento térmico (fase de vergatura) na resposta simultânea, do ponto de vista térmico e químico, de diferentes madeiras (castanheiro português, carvalho americano e carvalho romeno) usadas no envelhecimento de aguardentes vínicas Para a determinação da temperatura da madeira recorreu-se a termopares do tipo K. Os compostos extraíveis da madeira (ácidos fenólicos, aldeídos fenólicos, cumarinas e aldeídos furânicos) foram analisados por HPLC. Os resultados evidenciam que a distribuição da temperatura ao longo da espessura da aduela e a composição química da madeira são influenciadas pela temperatura de vergatura e pela frequência do humedecimento, bem como pela espécie botânica da madeira. É demonstrado que a fase de vergatura é de extrema importância para a qualidade da vasilha não apenas pelo seu impacto nas 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 modifications Palavras chave: carvalho; castanheiro; tratamento térmico; modificações térmicas e químicas INTRODUCTION The wooden barrel quality, the chemical characteristics of brandies, namely low molecular weight extractable compounds that are released from wood to the distilled during the ageing process, and the sensory properties of aged brandies are largely determined 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 heated over a fire of wood chips with various techniques of spraying or swabbing with water to enable the bending of the staves to the concave shape of a barrel. Then, the barrel is placed again over the fire to heat the inner surface to cause significant toasting in order to modify the structure, the physical properties and the chemical composition of wood, and to confer a distinct character to the brandies aged in it. In the last twenty years several papers have focused on the study of variables that are relevant for the heat treatment and their effects on the phenolic composition of French oak wood (Chatonnet and Boindron, 1989; Chatonnet, et al., 1989; Sarni et al., 1990; Sarni et al. , 1991; Chatonnet, 1995) and American oak wood (Hale et al., 1999; Matricardi and Waterhouse, 1999). More recently the study has been extended to include Portuguese oak wood – Quercus pyrenaica Willd. (Canas et al., 2000a). However, the simultaneous response of different kinds of wood, namely oak from different geographical origins and chestnut, to the same temperature and moisture conditions of the heat treatment has never been analysed. The results of our previous studies have demonstrated that chestnut wood is suited for cooperage (Carva- lho, 1998) and has interesting properties for the ageing of brandies (Canas et al., 1999; Belchior et al., 2001; Caldeira et al., 2002). On the other hand, oak wood originated from Eastern Europe (Rumania, Ciência Téc. Vitiv. 22 (1) 5-14.2007