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.     

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.     

Role of Organic Acids in Maturation of Distilled Spirits in Oak Casks

Maturation of whiskies and brandies in oak casks proceeds by reducing the perception of less desirable aromas of new distillates. During maturation, extraction of wood components increases the solubility of distillate compounds which reduces their headspace concentration above the matured spirit. The origins of this interaction are changes in aggregation of ethanol due to increases in contents of organic acids. During wood maturation organic acid concentrations in spirits increase as a result of extraction from cask wood, oxidation of ethanol and evaporation of ethanol and water. The effect of such changes was simulated using a model whisky ester in aqueous solutions of ethanol with acetic acid, oak wood extracts and acid fractions from new and matured Scotch malt distillates.     

Sensory and Chemical Analysis of ‘Shackleton's’ Mackinlay Scotch Whisky

Three cases of Mackinlay's Rare Highland Malt whisky were excavated from the ice under Sir Ernest Shackleton's 1907 expedition base camp hut at Cape Royds in Antarctica in January 2010. The majority of the bottles were in a pristine state of preservation and three were returned to Scotland in January 2011 for the first sensory and organoleptic analysis of a Scotch malt whisky distilled in the late 1890s. Sensory analysis and the higher alcohol and maturation congener profiles describe a lightly peated malt whisky matured in American white oak sherry or wine casks. Analysis of process related compounds together with combined gas chromatography (GC) mass spectrometry and GC‐olfactometry analysis of fermentation related congeners show a distinctly ‘modern’ style of malt whisky. While Scotch malt whisky at the end of the 19th century was generally regarded as heavily peated and harsh in character, Charles Mackinlay & Co. Distillers were producing a malt whisky with an altogether more subtle character at their Glen Mhor distillery near Inverness. The sensory and chemical analysis of this unique whisky artefact significantly changes our understanding of the quality and character of Scotch malt whisky produced by our distilling forefathers.     

威士忌麦芽新酒在Oloroso雪莉桶陈酿两年后挥发性风味成分的变化

为了对比麦芽新酒及采用Oloroso雪莉桶陈酿两年麦芽威士忌的差异，按照相关国标方法测定两种酒品质指标，并采用气相色谱-质谱联用（GC-MS）技术检测其挥发性风味成分。结果表明，陈酿酒的风味和口感均优于麦芽新酒，两种酒感官指标、理化指标及卫生指标均符合相关国家标准。两种酒共计检出105种挥发性风味化合物，其中麦芽新酒、陈酿酒分别共检出85种、86种，主要为醛类、酯类、醇类及酸类，醛类含量由4.44 mg/L增加至10.53 mg/L，酯类含量由257.34 mg/L增加至289.20 mg/L，醇类含量25.26 mg/L增加至54.96 mg/L，酸类含量85.18 mg/L增加至88.97 mg/L。陈酿麦芽新酒橡木桶类型和地理环境的差异导致其挥发性风味成分的变化，Oloroso雪莉桶陈酿麦芽新酒2年后呈现良好的品质及风味，但距离威士忌成品尚有差距，还需继续桶陈监测最终达到风味协调所需要的时间。     

Methods for the analysis of Scotch whisky

The standard techniques for the analysis of Scotch whisky are non-specific. Methods are described for the determination of individual higher alcohols, esters, aldehydes and phenol using gas chromatography, for polyphenolic extractives and the products of ethanolysis of wood lignin using thin-layer chromatography, and for total acids, esters, aldehydes, tannins, phenols and sugars using volumetric and colorimetric methods.     

Phenolic compounds in oak wood extracts used in the ageing of brandies

The oak wood extracts used in brandy production are extremely varied because of the different ways in which they are made: by infusion, by boiling or by maceration, with or without prior physical or chemical treatment of the wood. Such extracts release a large quantity of phenolic compounds and a very small amount of partially degraded lignin into the brandy, unlike spirits aged in oak barrels. Among monomer compounds derived from lignin, the presence of vanillic and syringic acids, vanillin, syringaldehyde, coniferaldehyde and sinapaldehyde can be noted. In the wood extracts, phenolic compounds and aromatic acids frequently dominate the ligno-complex and aromatic aldehydes respectively, which is not the case in brandies. Two samples of liquid extracts of oak wood displayed statistically aberrant vanillin contents.     

Analytical Strategies to Confirm the Generic Authenticity of Scotch Whisky

The authenticity of a specific brand of Scotch whisky may be confirmed by comparing analytical data for suspect samples with reference to analytical ranges for the genuine brand. Wider generic authenticity issues exist when a product purports to be Scotch whisky when it has not been produced in Scotland in accordance with the legal definition of Scotch whisky. When such cases reach litigation, courts may ask chemists to analyse suspect products and draw conclusions on authenticity. This paper presents analytical profiles generated from a survey of Malt, Grain and Blended Scotch whiskies and compares the results with whiskies of other origins and examples of a diverse range of suspect products purporting to be Scotch whisky. The concentrations and ratios of concentrations of the major volatile compounds (or congeners), particularly methanol, n‐propanol, isobutanol and 2‐ and 3‐methyl butanol, were found to be important factors in the authenticity decision‐making process. In addition, the absence of known Scotch whisky congeners, the presence of compounds known to be absent from genuine whisky and abnormal maturation congener profiles all contributed to the decision process. From this review of genuine analytical profiles, an experimental protocol for determining the authenticity of Scotch whisky is proposed.     

DETERMINATION OF ETHYL CARBAMATE IN DISTILLED SPIRITS USING NITROGEN SPECIFIC AND MASS SPECTROMETRIC DETECTION

Gas chromatographic methods are described for the determination of naturally occurring ethyl carbamate in distilled spirits at levels as low as 5 ppb. Bottled products, such as whisky, gin and brandy, are extracted in the presence of n-propyl carbamate as internal standard and analysed by capillary column gas chromatography with either nitrogen specific or mass spectrometric detection. A shorter extraction procedure is satisfactory when the more sensitive and selective mass spectrometric detection is used. Direct sample injection without extraction may be used for higher alcoholic strength cask and new-make samples. Analysis of 181 blended Scotch whisky samples indicated ethyl carbamate concentrations ranging from 20 to 75 ppb. Concentrations in 48 malt whiskies ranged from 15–100 ppb. Ethyl carbamate was not detected in gin, vodka and rectified neutral alcohol. All concentrations in bottled product fell below the Canadian limit of 150 ppb in distilled spirits.     

Evaluation of a Brazilian Fuel Alcohol Yeast Strain for Scotch Whisky Fermentations

Traditionally, distilling companies in Scotland have employed a very limited number of yeast strains in the production of alcohol for Scotch whiskies. Recent changes such as the decline in availability of brewers' yeast as a secondary yeast strain and the availability of yeast in different formats (e.g., dried and cream yeast as alternatives to compressed yeast) have promoted interest in alternative Scotch whisky distilling yeasts. In previous work, we investigated different strains of yeasts, specifically Brazilian yeasts which had been isolated from and used in fuel alcohol distilleries. One of the Brazilian yeasts (CAT 1) showed a comparable fermentation performance and superior stress tolerance compared with a standard commercial Scotch whisky distilling yeast (M Type). The Brazilian CAT 1 yeast isolate was further assessed in laboratory scale fermentations and subsequent new make spirit was subjected to sensory analyses. The spirits produced using the Brazilian strain had acceptable flavour profiles and exhibited no sensory characteristics that were atypical of Scotch whisky new make spirit. This study highlights the potential of exploiting yeast biodiversity in traditional Scotch whisky distillery fermentation processes.     

Addition of yogurt to wort for the production of spirits: Evaluation of the spirit aroma over a two-year period

Triggered by the development of lactic acid bacteria (LAB) during the production of Scotch whisky, this study examined the influence of yeast and LAB inoculation on whisky flavor. Four new spirits were produced using the same process. LAB were added as a form of a Greek yogurt's live culture. In each category (barley and rye), one sample was fermented with Greek yogurt while the other was fermented without it. The spirits were matured and analyzed at five different points. Results from gas chromatography-mass spectrometry (GC-MS) analysis showed basic volatile compounds, along with some important extra compounds with yogurt culture. The most obvious differences were observed in the concentration of butanoic acid, a characteristic acid in spirits undergoing lactic acid fermentation: to identify esters such as ethyl butanoate, ethyl isobutanoate, isoamyl butanoate, and 2-phenylethyl butanoate, they are not typical compounds in whisky.     

The Survival of Limit Dextrinase during Fermentation in the Production of Scotch Whisky

Limit dextrinase, is an important enzyme in the hydrolysis of starch from cereals to fermentable sugars. Work is described which demonstrates the importance of this enzyme in the production of Scotch whisky. The study considers the occurrence, survival and action of limit dextrinase (total and free) during fermentation in malt and grain distilleries. The results of both laboratory and distillery studies revealed that limit dextrinase can survive the conditions encountered during mashing and is not only present in the fermenter but its activity can increase during fermentation. This observation has important implications for the production of Scotch whisky, since the fermentation substrate (wash) is not boiled, the enzyme is therefore available to degrade dextrins into fermentable sugars, and can potentially increase the yield of alcohol.     

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     

Aging marker profile in cachaça is influenced by toasted oak chips

Cachaça is the most important distilled spirit in Brazil and the fourth most consumed in the world. Aging is not mandatory for cachaça. When aging is carried out, casks generally do not undergo the final wood toasting. However the level of thermal degradation of wood influences the formation of new chemical compounds, which are released during the aging process and improve the quality of the spirit. The objective of this study was to verify the influence of origin of wood and toasting intensity of oak chips on the profile of aging markers in cachaça. Staves of oak wood from the forests of Allier, Vosges and Nièvre (France) were milled and screened at 9 mesh. The chips underwent light, medium and heavy toasting. The toasted chips were added to cachaça (1 g/L) and kept in a closed system at room temperature, without agitation, for 15 days. The aging congeners (gallic acid, 5‐hydroxymethylfurfural, furfural, vanillin, vanillic acid, syringaldehyde, sinapaldehyde, syringic acid and coniferaldehyde) were analysed using HPLC. The increase in toasting intensity enhanced the content of the aging markers in cachaça, especially syringic acid, vanillin, syringaldehyde, coniferaldehyde and sinapaldehyde. The generation of aging marker compounds was influenced only by the toasting intensity and not by the origin of the oak wood. Copyright © 2015 The Institute of Brewing & Distilling     

Volatile Fatty Acids in Some Brands of Whisky, Cognac and Rum

SUMMARY— Gas chromatography was applied to eight different types of whisky, two of cognac, one of brandy, and four of rum to determine the relative proportions of volatile fatty acids; with the lower molecular acids as free acids, but upwards from caprylic acid as methyl esters. Acetic acid and the total amount of volatile acids were measured quantitatively. Rum contained the largest amount of volatile acids, 600 mg/L, while one of the brands of Scotch whisky contained the least, 90 mg/L. Acetic acid represented 40–95% of the total amount of volatile acids in the whisky; for cognac and brandy, the value was .50–75%, and for rum 75–90%. The relative amounts have been reported for 21 acids, with acetic acid excluded. Capric, caprylic and lauric acid were the main components in whisky, cognac and brandy. Of the beverages analyzed, rum contained the largest quantity of lower fatty acids, particularly propionic and butyric acid; the main component of Jamaican rum was propionic acid. The main components of the group of long-chain fatty acids were myristic, palmitic and palmitoleic acids. Scotch whisky contained equal amounts of palmitic and palmitoleic acid; palmitoleic acid regularly appeared in smaller amounts in the other beverages     

The Identification and Behaviour of Branched Dextrins in the Production of Scotch Whisky

Application of high performance anion chromatography (HPAEC) to distillers worts was able to resolve a series of individual fractions (A, B, C, D, E and F) which eluted between α(1–4) linear dextrins (DP4-7) and which were ubiquitous in worts. Their positions in the chromatogram and their behaviour suggested that they might be α(1–6) branched dextrins. Two of these fractions (C and D) were purified and shown to be α(1–6) branched dextrins by treatment with an α(1–6) debranching enzyme (pullulanase). Further characterisation by HPAEC and Matrix Assisted Desorption Ionisation/Time of Flight (MALDI-TOF) mass spectrometry revealed that the unknown fractions, C and D, were α(1–6) branched dextrins consisting of 6 and 7 glucose units respectively. Possible structures were suggested for these two fractions and it was shown that they were comprised of maltosyl and maltotriosyl branches attached by α(1–6) links to maltotriose, maltotetraose and maltopentaose. The behaviour of these dextrins was studied in the context of the Scotch whisky process under both laboratory and production conditions and they were found to be important substrates for the debranching enzyme, limit dextrinase, during fermentation. The study of these dextrins provided a useful tool for monitoring the effects of enzymes (α-, β-amylase and limit dextrinase) in the Scotch malt whisky production process.     

Headspace Congeners of Blended Scotch Whiskies of Different Product Categories from SPME Analysis

Flavour congeners in headspaces of 40 blended Scotch whiskies, of 4 different product categories (Deluxe, standard, retailer and West Highland), were collected by solid phase micro extraction (SPME) over 10 ml diluted (23% abv) whisky. Fibres (100 μm diameter) were thermally desorbed for 5 min in a split/splitless injection port and congeners quantified by high resolution gas chromatography. Two bonded SPME phases (polydimethylsiloxane and polyacrylate) were evaluated: exposure time was varied between 5 and 30 min; with whisky at either nosing (25°C) or tasting (37°C) temperature. Optimal analysis was with polyacrylate fibres at 37°C for 15 min but extraction at 25°C generated data relevant to sensory (nosing) data. Principal component (PCA) and discriminant partial least square (DPLS) analyses of mean % peak areas for all 57 resolved HRGC components and congeners (38) common to all whiskies gave product spaces showing clear separation of Deluxe, retailer and West Highland blends, but dispersed standard blends. In DPLS2 product clustering was similar whether relative (%) or absolute peak area was used in analyses but congeners loadings differed. From product spaces it was possible to assess contributions of flavour congeners, mainly esters and alcohols, to headspaces of individual blends and product categories.     

THE PRODUCTION OF AROMA COMPOUNDS BY YEAST

The yeast plasma membrane regulates the movement of compounds into the yeast cell and of yeast metabolites from the cell into the medium. The rate of penetration of organic acids into the yeast cell depends on their lipophilic nature, and on their molecular size and degree of branching. During fermentation yeast synthesizes a vast number of aroma compounds. The numerically and quantitatively largest groups of aroma compounds include fusel alcohols, fatty acids and fatty acid esters. The yeast used and the fermentation conditions can influence the formation of aroma compounds. The yeast also has a profound effect on the formation of other aroma compounds, such as sulphur compounds and phenols. In addition to fermentation, the maturing of a beverage can also influence the aroma. During the maturing lactones, phenols and other compounds are extracted from the oak casks in which the beverage is aged. The presence of the so-called “whisky lactone”, β-methyl-γ-octalactone, is characteristic of a beverage that has been matured in oak.     

Measurement of Thresholds for Reference Compounds for Sensory Profiling of Scotch Whisky†

Sensory profiling of Scotch whiskies, important for research and product analysis, requires training of assessors including the identification of important whisky aroma characters. Seventeen compounds were selected as potential reference standards for common whisky sensory characteristics. Nineteen assessors determined detection and recognition thresholds for each reference standard dissolved in 3 year old grain whisky at 23% (v/v) ethanol using both ascending dilution series and Latin square presentations. With the former, order effects and errors of habituation and anticipation were apparent. However, the Latin square presentation was satisfactory for threshold measurements in whisky, yielding good correlations and reproducibility, and enabling outliers to be reassessed independently. Slopes obtained from plotting probit against concentration for detection and recognition data, psychometric functions of aroma perception, varied between reference compounds and 90% recognition concentrations were obtained for each aroma standard. Sixteen of the compounds assessed were suitable for use as reference flavour standards for training of whisky assessors.