COMPARISON OF SCOTCH MALT WHISKY MATURATION IN OAK MINIATURE CASKS AND AMERICAN STANDARD BARRELS

The sensory and chemical attributes of Scotch malt distillate matured in uncharred, American white oak casks, were compared with distillate matured in miniature casks of similar wood with a capacity of 6 Litres. The maturation profiles of the two types of casks differed in the pattern of extraction of wood components and in the flavour characteristics of the final distillates. The product from the miniature cask maturations was not comparable with a Scotch malt whisky, due to differences in the ratios of concentrations of extractives. This may relate to differences in oxidation rates in the two cask types.     

Aroma compounds in barrel aged apple distillates from two different distillation techniques

The major fermentation and maturation related congeners in apple distillates from two different distillation techniques (alembic and column), matured in oak for 18 months, were measured by GC‐MS and HPLC. Together with a higher ethanol content, column distillates had higher ethyl acetate, methanol and n‐propanol levels compared with alembic distillates. A higher content of acetaldehyde was characteristic of the alembic distillates. The concentrations of i‐butanol, n‐butanol, amyl alcohols and n‐hexanol were not affected by the distillation technique used. Increasing the ageing time of distillates in oak resulted in an increase in the contents of acetaldehyde, ethyl acetate and amyl alcohols while the content of methanol decreased during ageing. Throughout ageing, there were no significant changes in the concentrations of n‐propanol, i‐butanol, n‐butanol and n‐hexanol. Among the maturation related compounds, gallic acid, ellagic acid, vanillin and syringaldehyde were determined in apple distillates with ellagic acid being the most abundant. The contents of gallic acid and ellagic acid increased during ageing whereas vanillin and syringaldehyde slightly increased throughout the 18 months of maturation. © 2019 The Institute of Brewing & Distilling     

Changes in colour and phenolic composition during the early stages of maturation of port in wood,stainless steel and glass

Differences in colour and phenolic composition during the maturation of port in oak wood, stainless steel and glass were examined for a period of 311 days at 18 °C. Principal component analysis (PCA) was used in variable selection, data reduction and data analysis. Nine out of 13 colour and phenolic variables were heavily loaded on PC1 (76.1% of explained variance), and a plot of PC1 scores versus maturation time showed differences in colour and anthocyanins between ports matured in different containers. Ports matured in oak casks developed at a faster rate than the other ports. Total phenolics remained fairly constant in all ports, as monomeric anthocyanins were rapidly depleted during the time of maturation. Polymeric pigments formed during maturation contributed to increases in colour density, hue and the rate of browning. Differences in redox potential between wood matured ports and non‐wood matured ports indicated that there were differences in dissolved oxygen which could have affected the maturation rate of these wines. © 2001 Society of Chemical Industry     

Maturation related phenolic compounds in cachaça aged in new oak barrels

Aging cachaça in wooden barrels improves its chemical and sensory profile and adds quality. Maturation of distilled spirits is influenced by factors such as the species of wood to make the barrels, degree of internal toasting, number of uses of the barrel and aging time. The level of maturation of distillates can be determined based on the concentration of age marker phenolic compounds extracted from the lignin of the wooden barrel, as well as their relationships with each other. This study characterises the aging process of cachaça by analysing the mechanism of lignin degradation during maturation in new oak barrels for up to 60 months in order to establish the relationship between the age of the distillate and the content of phenolic compounds extracted from the wood. The evaluation was based on the analyses of liginin derived compounds using high‐performance liquid chromatography. The level of maturation of aged cachaça can be characterised by evaluating the low molecular weight lignin‐derived phenolic substances. The total amount of benzoic acids (vanillic and syringic acids) can be taken into consideration for predicting the level of maturation of distillates. Based on the composition of maturation related congeners, it is likely that for cachaça, each year of aging in new oak barrels corresponds to approximately five years of aging for spirits in general. © 2020 The Institute of Brewing & Distilling     

The effect of successive uses of oak barrels on the extraction of oak-related volatile compounds from wine

Changes in the concentration of furfuryl compounds, guaiacol and 4‐methylguaiacol, cis‐ and trans‐oak lactone, and vanillin were studied during the maturation of wines in oak barrels of different origins (French oak and American oak). The rate at which these volatile compounds accumulated in the wines followed a curve that fits to mathematical models. The changes in concentration were usually consistent with diffusion kinetics. When the barrels are new, the concentration gradient between the wood surface and the wine is high, so diffusion occurs quickly, especially in the case of lactones, the extraction rate of which could be fitted to a power curve. After some time of maturation, the concentration gradient is not so large and furthermore, the wood surface may be exhausted of some compounds so the rate of extraction decreases. During the second fill, the rate of accumulation of these compounds in the wine was almost linear, especially during the first 6 months of storage, and the quantities measured in wine were much lower. The concentration of some compounds, increased during the final 3 months (between days 180 and 270), exhibiting a quadratic curve when plotted. Furfuryl aldehydes behaved differently as they are extracted very rapidly from the first millimetres of wood surface and transformed into furfuryl alcohol, a compound with no organoleptic significance.     

Agglomeration of ethyl esters in model spirit solutions and malt whiskies

Medium- and long-chain ethyl esters were found to have a limited solubility when model spirits and malt distillates were diluted to 230 ml ethanol per litre for sensory analysis. At concentrations above this critical level the concentration of esters in solution remained constant, with the excess esters forming agglomerates. The saturated nature of the solution reduced the volatility of other esters, with a proportion of these compounds being partitioned into the agglomerate. The distribution was dependent on the mole fraction of each ester and its activity coefficient. Dissolution of wood extractives caused a number of changes in the solubility parameters of organic compounds; activity coefficients were increased and both the concentration and activity at which agglomeration occurred were decreased. This resulted in lower solution concentrations with increased concentrations in agglomerates. The reductions in free solution concentration could result in lower headspace concentrations, and thus have a direct effect on the flavour of the matured spirit.     

Effect of ellagitannins,ellagic acid and volatile compounds from oak wood on the (+)‐catechin,procyanidin B1 and malvidin‐3‐glucoside content of model wines

Background and Aims: During ageing in oak barrels, wine undergoes changes because of the release of polyphenols and other molecules from wood. The aim of this study was to evaluate the influence of some oak wood‐derived volatile compounds, ellagic acid and oak wood extracts on the levels of (+)‐catechin, procyanidin B1 and malvidin‐3‐glucoside. Methods and Results: Phenolics and the oak wood derived volatile compounds studied were quantified by HPLC and by GC, respectively. Additionally, the new compounds formed in the solutions were characterised by their spectral properties. Ellagic acid and/or oak wood extracts slowed the decline in the levels of (+)‐catechin and procyanidin B1. In contrast, the decrease in malvidin‐3‐glucoside was more pronounced in the presence of ellagic acid and oak wood chip extracts. Furfural slowed (+)‐catechin degradation, while breakdown of malvidin‐3‐glucoside was slightly more pronounced in the presence of guaiacol, furfural, vanillin and eugenol. (+)‐Catechin, procyanidin B1 and malvidin‐3‐glucoside did not significantly affect the rate of the degradation of ellagitannins during the storage time studied. Finally, new HPLC peaks were detected in the solutions containing (+)‐catechin and ellagic acid, as well as with malvidin‐3‐glucoside with ellagic acid and oak wood extract. Conclusions: Malvidin 3‐glucoside and (+)‐catechin and procyanidin B1 presented distinct behaviours during time in the presence of volatile and non‐volatile compounds from oak wood. Significance of the Study: This work points out the importance of oak wood components in the degradation of anthocyanins and tannins, as well as the reactions that occur during the ageing of red wine.     

Effect of oak wood on the quality of beer

Maturation in wood is an important practice that is widely used in the production of high‐quality beverages. The effect of French oak cubes on young lager beer was studied. Oak cubes (with light, medium or heavy toasting) were added to the beer, which was stored at 0°C for 3 months. Beer samples were analysed monthly, and an acceptance test was performed at the end of 3 months. The content of volatile compounds (aldehydes, esters and higher alcohols) was determined by gas chromatography using a flame ionization detector, and the content of low molecular weight phenolic compounds was determined by high‐performance liquid chromatography. The contents of aldehydes, esters, higher alcohols and wood‐derived compounds increased during the 3‐month maturation period. Lager beer stored with heavily toasted oak cubes had the highest concentration of low‐molecular‐weight phenolic compounds, followed by the beer matured in an oak barrel. These results suggest that beer maturation in wood barrels or with oak cubes changed the composition of their oak‐related aromatic compounds, indicating that interactions between the beer and the wood occurred. Copyright © 2015 The Institute of Brewing & Distilling     

Chemical and sensory changes in fresh cider spirits during maturation in inert containers

BACKGROUND: Fresh cider spirits are alcoholic beverages mainly constituted by volatile compounds from apples that are formed during fermentation or generated during distillation. In this study the chemical and sensory changes that take place during the maturation of fresh cider spirits in inert containers made of stainless steel and glass were investigated. RESULTS: The type of container did not influence the maturation process for any of the studied compounds. Esterification, acetalisation and hydrolysis reactions occurred during the maturation of cider distillates over 24 months, giving rise to several changes in the original composition of this alcoholic beverage, but neither oxidation nor evaporation reactions were detected. A decrease in ethyl acetate, ethyl lactate, diethyl succinate and acetal was observed and an increase in fatty acid ethyl esters and 1,1,3‐triethoxypropane. Likewise, the sensory evaluation of the spirits was significantly influenced by the maturation time, with matured samples obtaining higher scores than fresh ones. CONCLUSION: The presence of reactive compounds in recently distilled products makes a period of around 12 months of maturation advisable to reach equilibrium and to improve the sensory assessment of cider distillates consumed in the fresh state. Copyright © 2010 Society of Chemical Industry     

Formation of volatile and maturation‐related congeners during the aging of sugarcane spirit in oak barrels

The aging process of distilled spirits is a complex system based on the extraction of molecules from the wood and interactions with the liquid, the phenomenon of migration of wood constituents, as well as the formation and degradation of several compounds. Volatile and maturation‐related congeners were evaluated during the aging process of cachaça, a Brazilian sugarcane spirit aged in oak barrels. Aged cachaça presented alterations in the levels of ethanol, higher alcohols, acetaldehyde, volatile acidity, ethyl acetate, total volatile congeners, isoamyl alcohol, ethyl carbamate and copper. The aging markers (gallic acid, furfural, 5‐hydroxymethylfurfural, vanillic acid, syringic acid, vanillin, syringaldehyde, sinapaldehyde and coniferaldehyde) were compared with the compounds found in whisky, cognac, armagnac, bourbon and brandy. Monitoring the generation and evolution of congeners during the aging process allowed the characterization of cachaça and the identification of product maturity. Copyright © 2014 The Institute of Brewing & Distilling     

Consideration of the influence of aging process,type of wine and oenological classic parameters on the levels of wood volatile compounds present in red wines

The contents of the volatile compounds extracted from wood: cis- and trans-whiskylactones, vanillin, syringaldehyde, furfural, 5-methylfurfural, eugenol, guaiacol, p-ethyl-phenol and p-ethylguaicol have been studied in 12 single-variety wines aged in new American oak barrels. The concentration of these compounds were determined after the following combinations of time in wood and time in bottle: 0 months in wood plus 18 months in bottle, 4 months in wood  + 14 months in bottle, 9 months in wood + 9 moths in bottle and 12 months in wood + 6 months in bottle. According to the composition of the wines, it is possible to conclude in general, that, the extraction of these compounds was faster during the first four or 9 months of aging in wood, depending on the wines. After 12 months of oak maturation, the extraction of these compounds slowed down. Furthermore, the final concentrations of these volatile compounds were different among studied wines. These differences could be related to some of the values of some of their oenological parameters, such as the contents of tartaric acid and sulphur dioxide of each wine.     

Chemical and sensory changes in white wines fermented in the presence of oak chips

Summary Three samples of French oak and one sample of American oak were analyzed by different gas chromatographic-mass spectrometric (GC/MS) methods. Two methods of quantifying the main volatile compounds in oak wood were compared, namely, Direct Thermal Desorption coupled with GC/MS and analysis of mixtures of water-ethanol and wines that had been in contact with oak chips by extraction using an organic solvent followed by GC/MS analysis of the extract. The ratio of the two oak lactones released into the wine by the oak chips was the same as the ratio observed in original, untreated wood. These substances are of particular sensory importance in wines aged in oak wood barrels. Thus, the use of oak chips in white wines may be advantageous. The wines steeped with the oak chips improved their acceptability rating 2 points on a scale of 9.     

Grape brandy production,composition and sensory evaluation

Grape brandy is a spirit drink produced by wine distillation and is matured in wooden casks. According to legislation, it can be characterised by the geographical area where the grapes were produced, the grape variety used and the selected distillation and ageing techniques. Distillation increases ethanol concentration and aromatic constituents which are already present in grapes or are developed during fermentation and distillation. During maturation in wooden casks, compounds that contribute to the aroma and taste are extracted from the wood. Hence the spirit acquires the desired softer mouth feel, aromatic complexity and overall quality. Different methods of analysis are used in order to pursuit this process by analysing volatile and non‐volatile substances and correlate composition with quality. Analysis can also be useful in identification of brandy safety, potential adulterations, provenance and differentiation from other spirits drinks. © 2013 Society of Chemical Industry     

Extraction of phenolics from new oak casks during spirit maturation: impact on spirit colour

The increase in colour and solubilisation of extract, polyphenols and ellagitannins were studied in wine spirit in new oak casks over a period of 23 years. Ellagitannins and oak colour were solubilised during the early years of maturation. After five years, the concentration of ellagitannins decreased markedly, while colour increased, although at a lower rate. Ellagitannins were oxidised into coloured polymers and hydrolysed into ellagic acid. The dry extract, containing polysaccharides, polyphenols and lignin, increased throughout maturation, growing quickly during the early years and slowly thereafter. In a model solution, ethanol exhibits a strong solvent effect. For higher concentrations (50% v/v and more), the extraction of colour was faster, and was typically dark yellow/brown with a red tone, attributable in part to the solubilisation of lignin and lignin by-products. © 2020 The Institute of Brewing & Distilling     

Extraction/oxidation kinetics of low molecular weight compounds in wine brandy resulting from different ageing technologies

This study provides innovative information on the influence of new technologies of ageing (stainless steel tanks with wood staves or wood tablets of chestnut or Limousin oak), in comparison with traditional technology (oak wooden barrels), on the extraction/oxidation kinetics of low molecular weight compounds of wine brandy. The brandy was sampled and analysed by HPLC during the first year of ageing. The results show that most of the compounds tend to increase over the time, but their extraction/oxidation kinetics depend on the ageing technology. The wooden barrels promote greater enrichment in the majority of the compounds. However, gallic acid, ellagic acid and syringaldehyde, and vanillin and 5-methylfurfural, which are strong antioxidants and key-odourant compounds, respectively, present higher contents in the brandy aged with the alternative technologies. Chestnut proves to be a suitable alternative to Limousin oak for the ageing of brandy in all the studied technologies, inducing faster evolution and high quality.     

Analysis of lignin from oak casks used for the maturation of Scotch whisky

Wood from four types of casks used for the maturation of Scotch whisky was analysed for free vanillin, syringaldehyde, vanillic and syringic acids and for milled wood lignin. Degradation of wood lignin by acidolysis was used to estimate the proportion of intact β-aryl ether linkages present. The yield of milled wood lignin was unaffected by repeated cask use. A comparison of acidolysis yields and the analysis of spirit matured for 3 years in each of the four types of cask indicated that the majority of β-aryl ether linkages in oak lignin are resistant to spirit hydrolysis and that cask exhaustion was not accompanied by significant delignification. Significant reductions in the concentrations of free guaiacyl and syringyl compounds were recorded for used casks and proved the best indicator of cask exhaustion.     

Effect of cider maturation on the chemical and sensory characteristics of fresh cider spirits

The influence of cider maturation on the chemical and sensory characteristics of fresh cider spirits was evaluated in the present study. To this end, a single-factor experiment with three maturation levels and five replicates (ciders) per level was developed. Level 1 corresponded to spirits obtained when alcoholic and malolactic fermentation of the ciders ceased, Level 2 corresponded to spirits obtained from ciders with a volatile acidity of 1.0 g/L acetic acid, while Level 3 corresponded to spirits made from ciders with a volatile acidity of 1.5 g/L acetic acid. Cider maturation significantly influenced the composition of the spirit as regards the ethyl esters of the major organic acids of cider (lactic, acetic and succinic). It also significantly influenced the content of aromas produced by bacterial activity (2-butanol, 2-propen-1-ol, 4-ethylguaiacol and eugenol), the concentration of which was found to increase with higher levels of maturation. The attributes “spicy” and “sweetness” were likewise influenced by the level of cider maturation. The distillates made from the most matured cider (volatile acidity 1.5 g acetic acid/L) scored better for “odour quality”.     

Effect of oak matrix (barrel and toasted chips) on the volatiles in Goji (Lycium Chinese) wine

The extraction efficiencies of volatiles from lightly toasted, medium‐toasted and heavily toasted oak chips with different solvents and the effect of oak matrix (chips and barrel) on the volatile composition of fermented Goji wine were surveyed. Of four different polarity solvents (water, ethanol, ether and dichloromethane), ethanol was the most effective solvent for the extraction of volatiles. The extraction efficiency of volatiles was related to the concentration of ethanol and the toast intensity of chips, and the most efficient extraction configuration was with 30% (v/v) ethanol and medium‐toasted chips. The effect of oak matrix on aroma composition and sensory characteristics of Goji wine was also evaluated. The changes in volatiles were related to the type of oak matrix. Odour activity value analysis and principal component analysis suggested that the effect of medium‐toasted chips on Goji wine was closest to an oak barrel. Sensory analysis showed that caramel, coffee, floral and vanillin flavour were enhanced in medium‐toasted chips, linked to the content of ethyl dihydrocinnamate, vaniliin and eugenol. Copyright © 2017 The Institute of Brewing & Distilling     

Oak barrel maturation vs. micro-oxygenation: Effect on the formation of anthocyanin-derived pigments and wine colour

The objective of this study was to check whether micro-oxygenation (MO) could mimic oak barrel ageing as regard the effect on wine colour. A red wine was submitted to micro-oxygenation for three months while another lot from the same wine was matured in oak barrels for three or six months. After these times, oak-matured and micro-oxygenated wines were bottled and analyzed six months later. The chromatic characteristics of these wines were also compared with those of a control wine that remained in a stainless steel tank all the time. Anthocyanins and anthocyanin-derived compounds were studied by LC–ESI-MS. Monomeric anthocyanins and other compounds including direct anthocyanin–flavanol adducts, ethyl-linked anthocyanin–flavanol compounds, and pyranoanthocyanins were detected. The application of MO for three months produced wines with a lower concentration of monomeric anthocyanins and a higher concentration of vitisin-related pigments than the control wine, the oak mature wines showing similar results than MO wines when aged for the same period of time. Differences were also observed in the chromatic characteristics, the micro-oxygenated and the oak matured wines showing a higher colour intensity than control wine. However, after six months in bottle differences were found between the micro-oxygenated wines and oak matured wines, the latter showing a more stable colour, probably due to the beneficial effects of compounds extracted from the wood (e.g. ellagitannins or wood aldehydes).