Effect of ageing system and time on the quality of wine brandy aged at industrial-scale

Efeito do sistema de envelhecimento e do tempo na qualidade da aguardente vínica envelhecida à escala industrial

 

Sara Cruz, Sara Canas^*, A. Pedro Belchior

INIAV - Dois Portos, Quinta d’Almoinha, 2565-191 Dois Portos, Portugal

^*Corresponding author:

 

SUMMARY

During the first six it was performed the analysis of dissolved oxygen dry extract polyphenol index chromatic characteristics and low molecular weight compounds of Lourinhã brandies aged in different systems 650 L wooden barrels (traditional system) and stainless steel tanks of 3000 L with wood staves (alternative system). In each system two kinds of wood were used simultaneously and arranged alternately: Portuguese chestnut (Castanea sativa Mill.) and Limousin French oak (Quercus robur L.) with medium plus toasting level. The quantity of staves was calculated in order to reproduce the surface/volume ratio of a 650 L wooden barrel. The results obtained show that the ageing system has a very significant effect on the chemical composition and colour of the aged brandies. The alternative system promotes further evolution of colour and lower oxygen consumption, while the traditional system yields higher dry extract total phenolic and low molecular weight compounds contents. These outcomes, which have been proven by an essay based on the dry extract method, indicate that the changes observed in the brandy during the ageing process are closely related to the wood shape, suggesting and the phenomena that occur in each ageing system are different. Regarding the ageing time, there is a highly significant effect on the characteristics of the aged brandies, even though the observations are made in a short period of time (minimum requested by the European legislation for the ageing of the wine brandy), with higher extraction of the wood compounds up to 90 days.

Key words: aged wine brandy, ageing system, ageing time, physicochemical characteristics, low molecular weight compounds.

 

RESUMO

Durante os primeiros seis meses de envelhecimento, procedeu-se à análise do oxigénio dissolvido, extrato seco, índice de polifenóis totais, características cromáticas e compostos de massa molecular baixa de aguardentes vínicas Lourinhã envelhecidas em diferentes sistemas: vasilhas de madeira de 650 L (sistema tradicional) e depósitos de aço inoxidável de 3000 L com aduelas de madeira (sistema alternativo). Em cada sistema foram utilizadas duas madeiras em simultâneo e dispostas alternadamente: castanheiro português (Castanea sativa Mill.) e carvalho francês Limousin (Quercus robur L.) com queima média mais. A quantidade de aduelas foi calculada de modo a reproduzir a relação superfície/volume de uma vasilha de 650 L. Os resultados obtidos revelam que a forma da madeira exerce um efeito muito significativo na composição química e na cor das aguardentes envelhecidas. O sistema alternativo promove maior evolução da cor e menor consumo de oxigénio, enquanto o sistema tradicional origina maior extrato seco, bem como maior teor de polifenóis totais e de compostos de massa molecular baixa. Estes resultados, comprovados através de um ensaio baseado no método de determinação do extrato seco, indicam que as modificações observadas na aguardente durante o processo de envelhecimento se encontram estreitamente relacionadas com a forma em que a madeira é usada, sugerindo que os constituintes e os fenómenos que ocorrem em cada sistema de envelhecimento são diferentes. Relativamente ao tempo de envelhecimento, existe um efeito altamente significativo nas características das aguardentes envelhecidas, mesmo num período curto de tempo (o mínimo requerido pela legislação europeia para o envelhecimento de aguardente vínica), verificando-se maior extração dos compostos da madeira até aos 90 dias.

Palavras-chave: aguardente vínica envelhecida, sistema de envelhecimento, tempo de envelhecimento, características fisico-químicas, compostos de massa molecular baixa.

 

INTRODUCTION

The quality of the aged wine brandy is determined by the distillate characteristics and the transformations that occur during the ageing process (Puech et al., 1998; Canas et al., 1999; Canas et al., 2000a; Belchior et al., 2001; Canas et al., 2002; Belchior et al., 2003; Patrício et al., 2005; Caldeira et al., 2006). According to the Regulation CE No 110/2008, six months is the minimum period of ageing in wooden barrels without which the wine brandy cannot be sold for consumption.

During the ageing process in wooden barrels, complex changes such as reactions between distillate compounds, reactions among extractable wood compounds, impregnation of brandy in the wood, as well as release of extractable compounds from the wood into the brandy (Puech et al., 1984; Singleton, 1995; Canas et al., 2002) that occur in the presence of oxygen (Belchior and San-Romão, 1982; Moutounet et al., 1998), along with the evaporation and concentration phenomena (Puech et al., 1998; Canas et al., 2002; Patrício et al., 2005). These transformations are influenced by the wood chemical composition, which is mainly dependent on the botanical species (Fengel and Wegener, 1989; Mosedale, 1995; Canas et al., 1999; Canas et al., 2000a; Jordão et al., 2005; Prida et al., 2006), the geographical origin (Canas et al., 2000b; Doussout et al., 2002), the seasoning and the heat treatment during barrel making (Sarni et al., 1990; Belchior et al., 2001; Canas et al., 2007), the barrel size (Belchior et al., 2005; Canas et al., 2008), as well as the cellar environment (Mosedale, 1995; Singleton, 1995).

The oak species that stand out are: Quercus robur L. predominantly from the Limousin region (France), Quercus sessiliflora Salisb., especially from the Allier region (France) and Quercus alba) L.(USA). However, the research that has been performed on chestnut wood Castanea sativa Mill.) proved its suitability for this purpose (Canas et al., 1999; Canas et al., 2000a; Belchior et al., 2001; Caldeira et al., 2006; Canas et al., 2011).

Nevertheless, the need to optimize and reduce the costs of the brandy’s ageing in the traditional system in wooden barrels, such as the invested capital in brandy and wooden barrels for a long period, and the sustainable utilization of wood, encourage the search for alternative ageing systems.

Several studies were conducted using alternative systems for the ageing of wine (Araptisas et al., 2004; Eiriz, 2007; Nevares and Del Álamo et al., 2010; Cabrita et al., 2011), as well as for the ageing of its derivatives: vinegar (Morales et al., 2004; Tesfaye et al., 2004) and wine brandy (Belchior et al., 2003; Madrera et al., 2003; Canas et al., 2009a,b; Caldeira et al., 2010). Alternative systems for ageing other drinks such as cider, rum, whiskey and sake have also been target of research (Martinez et al., 2001; Chang et al., 2004; Fan et al., 2006. It was showed that the quality of the final product in alternative ageing systems depends on the shape and size of the wood used, the dosage, the heat treatment and the botanical species, since these factors influences the kinetics of extraction/oxidation and diffusion of the wood extractable compounds (Afonso, 2002, Fan et al., 2006), along with the contact time between the wood and wine, and the possibility of using micro-oxygenation (Piracci et al., 2001). In the attempt to simulate similar conditions to those of the wooden barrels using stainless steel tanks, promising results were obtained in red wine namely the colour stabilization, and the decrease of astringency and herbaceous notes (Kelly Wollan and, 2003).

In this context, Belchior et al. (2003) performed a first approach, at laboratorial-scale, of Lourinhã wine brandy ageing with small logs and chips of Limousin oak and chestnut wood. Recently, in a project on a pilot scale, studies were conducted to evaluate the effects of different ageing systems – wooden barrels, staves and tablets with equal surface/volume ratio - along with the botanical species (Limousin oak and chestnut) and oxygenation, in the physicochemical characteristics and sensory properties of a Lourinhã brandy over two years and a half of ageing (Canas et al., 2009a,b; Caldeira et al., 2010). The results showed that alternative systems seem to accelerate the ageing process and originate wine brandy with different physicochemical characteristics and sensory properties. Moreover, the close relationship found between the ageing systems and the characteristics of wine brandies led to conclude that many constituents and phenomena governed by several ageing factors should be involved. It was also verified that chestnut wood has great interest to brandy ageing, whatever the ageing system. These results indicate that modifications observed in the brandies are closely related to the kind of ageing system.

The present work, aims to deepen the technical and scientific knowledge about the two kinds of ageing systems in order to obtain reliable results on their potential for the ageing of wine brandy, based on the evaluation of dry extract, total phenolic content, chromatic characteristics, low molecular weight compounds and dissolved oxygen of a Lourinhã brandy aged in 650 L wooden barrels and in stainless steel tanks of 3000 L with wood staves.

 

MATERIAL AND METHODS

Experimental design and brandy sampling

The same Lourinhã wine distillate (77.2 % v/v) was aged in two different ageing systems: 650 L new barrels and 3000 L stainless steel tanks with wood staves, in duplicate. In each system two different kinds of wood were used simultaneously and arranged alternately: Portuguese chestnut (Castanea sativa Mill.) and Limousin oak (Quercus robur L.). The barrels and the wood staves were manufactured by J. M. Gonçalves cooperage (Palaçoulo, Portugal) with medium plus toasting level. The barrels were heated over a fire of wood offcuts and the staves were heated in an oven. The quantity of staves (91 cm length x 5 cm width x 1.8 cm thickness) was calculated in order to reproduce the surface area to volume ratio of a 650 L barrel. The wooden barrels and the stainless steel tanks were placed at Adega Cooperativa de Lourinhã in similar cellar conditions. The brandies were sampled and analysed after 8, 15, 90 and 180 days of ageing; a total of 16 samples were taken.

Determination of dry extract

The dry extract of brandies was analyzed according to the usual method of OIV (OIV, 1994).

Determination of total polyphenol index

The total phenolic content of the brandies was determined by the absorbance at 280 nm (Ribéreau-Gayon, 1970). Brandies were diluted with ethanol/water 75:25.

Determination of chromatic characteristics

The chromatic characteristics (CIELab) were determined with a Varian Cary 100 Bio spectrophotometer (Palo Alto, USA) and a 10 mm glass cell, by measuring the transmittance of the brandy every 10 nm from 380 to 770 nm, using a D65 illuminant and a 10º standard observer. The parameters measured were: lightness (L*); saturation (C*); chromaticity coordinates (a* and b*). Coordinate a* takes positive values for reddish colours and negative values for greenish ones, whereas coordinate b* takes positive values for yellowish colours and negative values for bluish ones. In addition, the brown colour of the brandies was measured by the absorbance at 470 nm (Martins and Van Boekel, 2003), which was calculated from the value of transmittance at 470 nm provided by CIELab output.

Analysis of low molecular weight phenolic compounds and furanic derivatives by High Performance Liquid Chromatography

Samples of brandies were added with an internal standard (4-hydroxybenzaldehyde, 20 mg/L), filtered through 0.45 µm membrane (Titan) and analysed by direct injection of 20 µL. Chromatography was performed as described by Canas et al. (2003), with a HPLC Lachrom Merck Hitachi system equipped with a quaternary pump L-7100, a column oven L-7350, a UV-Vis detector L-7400, and an autosampler L-7250, coupled to a HSM D-7000 software (Merck) management, acquisition and treatment data. The identification of chromatographic peaks was made both by retention time and UV-Vis spectra matching with standards. The chromatographic purity of the peaks and the UV-Vis spectra (200-400 nm) were performed using a Waters system equipped with a photodiode-array detector (Waters 996), with the same chromatographic conditions, managed by “Millennium 2010” software (Waters, Milford, USA).

Determination of dissolved oxygen

Dissolved oxygen in brandies was determine with an Oximeter Oxi 340-b (WTW, Weilheim, Germany). Corrections for the temperature, dry extract and alcohol content of the brandies were made according to Mourges et al. (1973).

Statistical analysis

The two-way analysis of variance (ANOVA) was performed to evaluate the effects of ageing system and ageing time on the characteristics of the aged brandies, as well as on the essay based on the dry extract method. Fisher’s least significant difference (LSD) test was applied to compare the different averages. All the calculations were carried out using Statistica vs ’98 edition (Statsoft Inc., Tulsa, USA). The correlation analysis was performed using Statgraphic v.5 (STSC Inc., Rocksville, USA).

 

RESULTS AND DISCUSSION

Effect of the ageing system

The ageing system has a highly significant effect on the dry extract, total polyphenol index, luminosity and dissolved oxygen of the aged brandies (Table I), and a significant effect on the coordinate a*. The absorbance at 470 nm that is a reliable indicator of the melanoidins content (Martins and Van Boeckel, 2003) is very significantly influenced by this factor.

 

 

Brandies aged in wooden barrels present higher dry extract and higher total polyphenol index, but lower colour intensity (inversely proportional to luminosity), lower red hue (a*) and brown hue (A 470) than those aged in stainless steel tanks with wood staves. Therefore, the greatest enrichment of the chemical composition of the brandies does not correspond to a greater colour evolution, contradicting the results obtained in several essays performed on the ageing of brandies in the traditional system (Canas et al., 2000a; Belchior et al., 2001; Canas, 2003).

During ageing the brandy is enriched in wood extractable compounds, which contribute to its dry extract. The contents of such compounds depend both on the wood botanical species and the heat treatment of the barrel (Câmpeanu et al., 1992). The heat treatment of the wood used in the two ageing systems is theoretically the same, although it has a greater effect on the extraction of compounds from the barrels than from the staves. This variability should be partially attributed to the different kind of heat processes applied together with the wood shape.

Concerning the total phenolic content, given that the distillate has no phenolic compounds (Canas, 2003) the difference found can be due to the influence of the ageing system. The highest total polyphenol index of brandies aged in wooden barrels may be related to the higher extraction/diffusion rate of phenolic compounds.

According to Belchior and San-Romão (1982), the extraction of compounds from wood already involves some oxidation, therefore the lowest dissolved oxygen content (corresponding to higher consumption) and the highest content of phenolics detected in the brandies aged in wooden barrels seem to be linked.

It should be noted that the values of dry extract and total polyphenol index show high correlation (r=0.98), which is in agreement with the results obtained by Canas et al. (2009b).

As for the chromatic characteristics, there is a faster evolution of colour in the brandies aged in stainless steel tanks, shown by greater colour intensity and red hue. Although not significant, saturation and yellow hue behave similarly. It is verified that the colour of the brandy aged in tanks results from a more intense red-yellow combination.

Belchior (1983) found a direct relationship between the total phenolic content and the colour of the aged brandy, and Bakker et al. (1986) report that the luminosity is inversely related to the content of phenolic compounds. Similar results were obtained in brandies aged in wooden barrels (Canas et al., 2000a; Belchior et al., 2001; Canas, 2003). In the present study, the correlations between the total polyphenol index and the chromatic characteristics, namely the brightness (r=-0.69) and the coordinate a* (r=0.51), are in accordance with the results obtained in the mentioned works. Therefore, the lowest total phenolic content and lightness of the brandies aged in stainless steel tanks with staves may arise from unknown reactions that can be associated with the use of two different wood species simultaneously and/or the presence of non-phenolic compounds, which have a great influence on colour, as observed by Canas et al. (2009b). On the other hand, the heat treatment can also be responsible for the observed effect, once the kind of heat intensity and the staves dimension can promote higher degradation of phenolic compounds (Sarni et al., 1990; Rabier and Moutounet, 1991; Canas et al., 2000c; Canas et al., 2007), as well as a more intense alteration of the wood structure (Hale et al., 1999). In addition, the Maillard reactions occurring during the heat treatment origin many volatile (Cutzach et al., 1997) and non-volatile compounds (Alanon et al., 2010) in the wood. Avakians et al. (1992) indicated that these reactions have great influence on the colour of the aged brandy. It is also known that among the non-volatile compounds resulting from the Maillard reactions, there are some key-chromophores (compounds with high impact on colour) which cause the yellow, red and brown hues (Hofmann et al., 1998; Gokmen et al., 2006). The melanoidins belong to this group of chromophores and are closely related to the brown colour in foods (Gokmen et al., 2006). In the case of wood, melanoidins are formed during the heat treatment (Borrelli et al., 2002).

It is important to point out that the relationship between the chemical composition and the colour of the brandy is different from that observed in red wines aged in different systems (Del Álamo et al., 2008, De Beer et al., 2009). This suggests that other compounds not quantified in the dry extract and in the total polyphenol index determine the colour of brandies. Addict to these factors, the acetaldehyde resulting from the oxidation of ethanol during ageing (Reazin, 1981; Nishimura et al., 1983), as well as some phenolic aldehydes such as vanillin (Es-Safi et al., 2000) and furanic aldehydes such as 5-hydroxymethylfurfural and 5-methylfurfural (Es-Safi et al., 2000) may also act in condensation reactions between phenolic compounds present in the brandy, particularly tannins, and influence the chromatic characteristics.

Comparing the absorbance at 470 nm of the brandies from the two ageing systems, there is a higher concentration of melanoidins in the brandies aged in stainless steel tanks with staves than in those aged in wooden barrels. Thus, the results of this study are in accordance with the hypothesis raised by Canas et al. (2009b), who consider melanoidins as another type of colouring compounds formed by the Maillard reactions, which are also present in toasted wood and are likely to be released into the brandy during the ageing process. On this basis, the highest intensity of toasting (Gokmen et al., 2006) may have favoured the formation and accumulation of these compounds in the corresponding staves and brandy, whose concentration did not affect the dry extract but considerably contributed to the colour.

Moreover, oxygen is a key element in the chemical changes of brandy during ageing (Avakiants, 1992; Puech and Mosedale, 1998), and it is analyzed in order to obtain more information on the phenomena involved in the evolution of the brandy’s composition during this process. Since there is a continuous and slow diffusion of oxygen through the bung and the wood in the barrels (Moutounet et al., 1998; Kelly and Wollan, 2003), which does not occur in stainless steel tanks during ageing, the lowest level of dissolved oxygen found in the brandies aged in wooden barrels seems to indicate a high consumption in this situation (Nevares et al., 2008; Canas et al., 2009a,b). Despite the surface/volume ratio was equal and the same botanical species were used in both systems, the differences observed in the brandies are possibly related with the extraction rate of compounds from the wood and their subsequent transformation in the brandy. Such transformation is associated with the reactions that occur during ageing - oxidations, esterifications, Maillard reactions, polymerizations and polycondensations. Puech and Mosedale (1998) state that oxidation is the most important, involving both the compounds of the distillate and from the wood. The oxidation may be specific to each ageing system and have contributed to the differentiation of brandies.

Concerning the low molecular weight compounds, the results of the analysis of variance (Table II) show a highly significant effect on the contents of 5-hydroxymethylfurfural, gallic acid, coniferaldehyde and sinapaldehyde, a very significant effect on the contents of ellagic acid and furfural, and a significant effect for syringaldehyde and the total content of compounds analysed. It should be noted that the total content of compounds is higher in brandies aged in wooden barrels, which can be distinguished particularly by the content of 5-hydroxymethylfurfural, gallic acid, coniferaldehyde and sinapaldehyde.

 

 

The contents of furanic aldehydes are higher in the brandies aged in barrels than in those aged in stainless steel tanks with staves (Table II). The furfural is quantitatively the most important compound of the aged brandies in both systems, not only due to its presence in the distillate (Jeuring and Kuppers, 1980; Canas et al., 2004; Caldeira et al., 2010), but also because it exhibits the highest extraction/diffusion rate in the aged brandy (Canas et al., 2004; Patrício et al., 2005). Moreover, furfural results from the degradation of hemicelluloses of the wood during the heat treatment. These polymers are those with lower thermal resistance (Fengel and Wegener, 1989) and hence are preferentially degraded, contributing to make furfural the main furanic derivative of the toasted wood (Rabier and Moutounet, 1991; Chatonnet, 1995; Canas et al., 2007) and of the corresponding brandies (Canas, 2003).

It is found that the content of phenolic acids is higher in brandies aged in wooden barrels (Table II). For gallic acid, the great difference between the ageing systems probably derives from the kind of heat treatment performed owing to the thermal sensitivity of this compound (Rabier and Moutounet, 1991; Canas et al., 2000c, 2007), which content usually tends to decrease from medium toast. Given that the melting point of the gallic acid is 249.9 °C, that is similar to the toasting temperature that the wood used in both ageing systems underwent, the results obtained suggest that the wood from barrels suffered the greatest accumulation of gallic acid. Indeed, since the surface/volume ratio is the same in both systems and therefore did not promote differences in the extraction process, the lowest content of gallic acid in the brandies aged in stainless steel tanks may be associated with a more intense degradation of this compound during the toasting of the staves due to their smaller thickness. The ellagic acid proceeds from the degradation of ellagitannins (Chatonnet, 1995). The high melting point of this acid (around 450 °C) allowing to its accumulation in the wood in the free form that can be release into the wine brandy during ageing.

Regarding the phenolic aldehydes, despite the observed variability in the brandies aged in each system, there is a higher concentration in those aged in wooden barrels, except for syringaldehyde (Table II). This fact may be related to the type of chemical reactions that occur in each system and the probability of triggering differently. However, syringaldehyde and vanillin have a complex profile extraction and may result from: i) very intense toasting; ii) more pronounced oxidative process in the wood and/or brandies, according to Puech (1984).

To better understand the results of this study, such as the fact that the brandies aged in wooden barrels present higher dry extract and higher total polyphenol index but less evolved chromatic characteristics than the brandies aged in stainless steel tanks with staves, it was performed an essay based on the dry extract method (OIV, 1984). For this purpose, it was used samples of the brandy with 90 and 180 days of ageing in one wooden barrel and in one stainless steel tank (four modalities), with three replications. In each modality the comparison was made between an aliquot of control brandy (C) with an aliquot of the same brandy subjected to the dry extract method and redissolved with an hydroalcoholic solution having the same pH and alcohol content of the control brandy (ES), in order to obtain relevant information about the possible modification of brandy’s compounds during the application of the method and its impact on the total polyphenol index and the chromatic characteristics.

The temperature of 100 °C (method conditions) does not affect significantly the majority of the extractable compounds of the brandy (Table III), although it is registered a highly significant decrease of furfural in the brandies aged in both systems, a significant increase in syringic acid in the brandies aged in stainless steel tanks with staves and a highly significant decrease of syringic acid in the brandies aged in wooden barrels (Table III). Since the furanic aldehydes are quantified in the dry extract but also in the total polyphenol index (Canas and Belchior, 2012), the detected alteration implies that the concentration of volatile compounds in the free form (more susceptible to evaporation, oxidation and/or involvement in other chemical reactions) decreases and thus leads to a decrease of its contribution to the total polyphenol index. Regarding the phenolic acids, their behaviour can be justified by oxidation and/or degradation during the essay, and appears to contribute to the decrease of the total polyphenol index. The difference of these acids behaviour in the hydroalcoholic solutions corresponding to each ageing system after applying the dry extract method, points out once again that the chemical reactions are likely specific in each ageing system. The concentration of phenolic aldehydes is lower in the hydroalcoholic solution than in the brandy after applying the dry extract method, except for sinapaldehyde. This outcome contributes to the decrease in total polyphenol index. The decrease of the content of vanillin results from its evaporation, as well as from some degradation phenomena, such as oxidation, that also affect the decrease of concentration of syringaldehyde and coniferaldehyde.

 

 

The results also demonstrate that the total polyphenol index is consistent with that obtained previously (Table I), being higher in the brandies aged in wooden barrels. After applying the dry extract method, it is verified that the total polyphenol index decreased, in which phenolic compounds and furanic derivatives are quantified (Canas and Belchior, 2012).

For the chromatic characteristics, the results obtained confirm what was previously reported (Table I). The increase of colour intensity after the application of the dry extract method in the brandies can be caused by a great contribution of the non-phenolic compounds. It is known that the combination of high values of coordinates a* and b* are associated with the topaz hue. In this assay the coordinates a* and b* do not undergo significant changes. However, despite the slight increase in the coordinate a* and A 470 after application of the method, it may have contributed to the evolution of the brandy’s colour towards topaz hue. This combined effect can result from the formation of non-phenolic pigments by temperature action and possibly by oxidation, supporting the hypothesis that the colour of aged brandies in different systems depends on the non-phenolic and/or volatile compounds.

 

Effect of the ageing time

The Figure 1 shows that the dry extract and the total polyphenol index of the aged wine brandies present a gradual increase, minor in the first 15 days of ageing, followed by a marked evolution between 15 and 90 days. The kinetics displayed are in accordance with the findings of Belchior et al. (2001), Canas et al. (2002) and Patrício et al. (2005). The dissolved oxygen decreases up to 90 days, followed by an increase up to 180 days of ageing. Similar results were reported by Canas et al. (2009a). This behaviour can result from a higher consumption of oxygen at the beginning of ageing owing to several reactions in which oxygen participates, particularly in the extraction of wood compounds (Belchior and San-Romão, 1982). At 180 days there is a further increase in the availability of dissolved oxygen, which can be associated with the predominance of extraction regard to oxidation.

 

Figure 1

 

Concerning the evolution of the chromatic characteristics, it is observed a continuous increase of saturation and a decrease of lightness, thereby being consistent with that described by Canas et al. (2009a). It is inferred that these kinetic may arise from the increase of phenolic and non-phenolic compounds in the brandy, and found a very strong correlation with the content of melanoidins. As can be seen in Figure 1, the value of A 470 nm presents a gradual increase even after 90 days of ageing, and between 90 and 180 days the increase becomes not significant, which may be partly explained by the high standard deviation associated with the sampling carried out at 180 days. The largest standard deviation at this ageing stage possibly reflects the influence of several factors: the wood intra-specific variability; the shape of the wood; the variability associated with the heat treatment to which the wood was subjected.

Evaluating the kinetics of the chromaticity coordinates (Figure 2), it is found that the raw distillate has a green colour (corresponding to a negative value of a*), while the colour exhibit by the aged brandies result from the combination of red (positive values of coordinate a*) and yellow (positive values of coordinate b*) hues. In the first 15 days of ageing, the evolution of red (a*) and yellow (b*) hues is higher than those of the brandies aged in wooden barrels. But after 90 days, in the brandies aged in stainless steel tanks with staves both hues progressively increase. In the brandies aged in wooden barrels, it is observed a gradual evolution of the coordinates a* and b* up to 15 days, but after 90 days the yellow hue becomes predominant since the b* coordinate increase and a* coordinate has a slight variation.

 

 

There are relevant changes in the furanic and phenolic composition of the brandies over the time, shown by the steady increase in the contents of all of the studied low molecular weight compounds (Figure 3). The 5-hydroxymethylfurfural, and especially the 5-methylfurfural, have a slow increase in the initial phase of ageing (first 15 days), whereas the furfural increase significantly in the same period of time. When comparing the first 15 days with 90 days of ageing, it is clear that the three furanic aldehydes have a significant increase. From 90 to 180 days the concentrations of furfural and 5-hydroxymethylfurfural not vary significantly. This behaviour may be related to the occurrence of condensation reactions between these compounds and phenolic compounds present in the brandy (Es-Safi et al., 2002). Distinctly the 5-methylfurfural continues to increase significantly from 90 to 180 days.

 

 

In the case of phenolic acids, the evolution between 8 and 15 days is only significant for syringic acid. After this phase vanillic and ellagic acids increase progressively up to 180 days. The kinetics of these acids may reveal the effect of the heat treatment of the wood in the brandy’s chemical composition (Nishimura et al., 1983; Rabier and Moutounet, 1991). Gallic and syringic acids do not show a significant increase between 90 days and 180 days, probably due to the high standard deviation, as mentioned before.

The phenolic aldehydes show similar kinetics, except for syringaldehyde. The contents of vanillin, coniferaldehyde and sinapaldehyde have only a significant increase from 15 to 90 days, which is consistent with the results of Belchior et al. (2001) and Canas et al. (2004), suggesting that the extraction kinetics is more pronounced in this period of time. The kinetics of syringaldehyde distinguishes itself by a significant increase throughout the ageing period studied. Recalling that the benzoic aldehydes (vanillin and syringaldehyde) mainly result from the oxidation of cinnamic aldehydes (coniferaldehyde and sinapaldehyde) proceeding from the lignin degradation during the heat treatment of the wood and/or its hydroalcoholysis during ageing (Puech, 1984), Quaresma (2000) states that the kinetics of vanillin and coniferaldehyde and those of syringaldehyde and sinapaldehyde appear to be related, since the slower increase of coniferaldehyde and sinapaldehyde corresponds to a continuous increase in the concentration of vanillin and syringaldehyde, respectively.

The analysis of interactions indicates that the kinetics of lightness and 5-hydroxymethylfurfural (highly significant), gallic acid (very significant), and coordinate a *, dissolved oxygen, A 470, syringic acid and 5-methylfurfural (significant) depend on the ageing system.

 

CONCLUSIONS

This study provides, for the first time, specific information about the physicochemical characterization of wine brandies aged in alternative systems at industrial-scale.

Under these experimental conditions, it is found that after six months of ageing the alternative system comprising stainless steel tanks with staves in contact with the wine brandy did not allow the acquisition of the physicochemical characteristics achieved by the same wine brandy aged in wooden barrels. However, the colour evolution is greater in the brandies aged in the alternative system, which raises issues regarding the relationship between the chemical composition and the chromatic characteristics of the wine brandy aged in different systems.

The brandies aged in barrels present higher dry extract, higher total polyphenol index and higher concentration of phenolic and furanic compounds, i.e., have the richest chemical composition, but lower chromatic evolution than the brandies aged in stainless steel tanks with staves. This negative correlation between chemical composition and the chromatic characteristics suggests the existence of unknown reactions that may have been caused by the use of two kinds of wood simultaneously, by specific phenomena in each ageing system, and/or the presence of non-phenolic compounds that influence the colour of the aged brandies.

The results obtained for the absorbance at 470 nm and from the dry extract essay reinforce the hypothesis of the crucial role of some non-phenolic compounds to the colour of the aged brandies, that may explains the apparent inconsistency between the chemical composition and the chromatic characteristics, as well as the difference to the positive correlations found in previous studies (Canas et al., 2000a; Belchior et al., 2001) on the traditional ageing of wine brandies.

Among the low molecular weight compounds of the studied brandies, the 5-hydroxymethylfurfural, gallic acid, coniferaldehyde and sinapaldehyde seem to be chemical markers of the ageing system.

Regarding the ageing time, there is a significant increase of furanic and phenolic compounds release from the wood into the brandy, which indicates that extraction was preponderant to oxidation in both ageing systems during the first six months of ageing.

The ongoing research of wine brandy ageing until the second year will provide information that may contribute to clarify the doubts about the role of phenolic and non-phenolic compounds on the chromatic characteristics, and also about the main related phenomena.

 

ACKNOWLEDGEMENTS

This work had the financial support of Tanoaria J.M. Gonçalves, Adega Cooperativa de Lourinhã and INIAV-Dois Portos.

 

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^*Corresponding author:

Tel.: +351 261712106; Fax: +351 261712426, E-mail: e-mail address: sara.canas@iniav.pt

 

(Manuscrito recebido em 15.11.2012. Aceite para publicação em 07.01.2013)