Whisky Samples Research Articles

Solid phase extraction, multidimensional gas chromatography mass spectrometry determination of four novel aroma powerful ethyl esters: Assessment of their occurrence and importance in wine and other alcoholic beverages

A method for the quantitative determination of four powerful aromatic ethyl esters recently identified in some wines has been developed, validated and applied to the determination of these compounds in different samples of wine, whisky and brandy. Ethyl 2-, 3-, and 4-methylpentanoate and ethyl cyclohexanoate are extracted from 100 ml of sample by solid phase extraction (SPE) on a 200 mg LiChrolut EN bed. Major compounds are eliminated by rinsing with a water–methanol (50:50) solution containing 1% sodium bicarbonate, and analytes are eluted with 1.5 ml of dichloromethane. Fifty microlitres of this extract are then injected in a multidimensional gas chromatography–mass spectromety (GC–GC–MS) system. Recoveries in the SPE are quantitative. Method repeatability is satisfactory (5–12% for a 5–10 ng l −1 level, and less than 7% for 25–50 ng l −1 level), the method linearity holds along the whole range of occurrence of analytes (2–2700 ng l −1), and the signal is independent on the matrix. Method detection limits are below 1 ng l −1 in all cases. Results suggest that these compounds are formed by the slow esterification with ethanol of the corresponding acids formed by different microorganisms. The levels of these compounds are above the corresponding thresholds in most samples of aged wines or distillates, but are particularly high in some sweet wines, whiskeys and brandies where they may constitute the most important contributors to the sweet-fruity notes reaching concentrations up to 85–350 times higher than the corresponding odor thresholds.

Comparative study of the whisky aroma profile based on headspace solid phase microextraction using different fibre coatings

A dynamic headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to ion trap mass spectrometry (GC– ITMS) method was developed and applied for the qualitative determination of the volatile compounds present in commercial whisky samples which alcoholic content was previously adjusted to 13% (v/v). Headspace SPME experimental conditions, such as fibre coating, extraction temperature and extraction time, were optimized in order to improve the extraction process. Five different SPME fibres were used in this study, namely, poly(dimethylsiloxane) (PDMS), poly(acrylate) (PA), Carboxen-poly(dimethylsiloxane) (CAR/PDMS), Carbowax-divinylbenzene (CW/DVB) and Carboxen-poly(dimethylsiloxane)-divinylbenzene (CAR/PDMS/DVB). The best results were obtained using a 75 μm CAR/PDMS fibre during headspace extraction at 40 °C with stirring at 750 rpm for 60 min, after saturating the samples with salt. The optimised methodology was then applied to investigate the volatile composition profile of three Scotch whisky samples—Black Label, Ballantines and Highland Clan. Approximately seventy volatile compounds were identified in the these samples, pertaining at several chemical groups, mainly fatty acids ethyl esters, higher alcohols, fatty acids, carbonyl compounds, monoterpenols, C 13 norisoprenoids and some volatile phenols. The ethyl esters form an essential group of aroma components in whisky, to which they confer a pleasant aroma, with “fruity” odours. Qualitatively, the isoamyl acetate, with “banana” aroma, was the most interesting. Quantitatively, significant components are ethyl esters of caprilic, capric and lauric acids. The highest concentration of fatty acids, were observed for caprilic and capric acids. From the higher alcohols the fusel oils (3-methylbutan-1-ol and 2.phenyletanol) are the most important ones.

Comparison of non-invasive NIR and Raman spectrometries for determination of alcohol content of spirits

The suitability of non-invasive NIR and Raman spectrometries for determination of % ethanol content has been investigated. Samples of whisky, vodka and sugary alcoholic drinks were analysed in 200 mL (flat) and 700 mL (round) glass bottles. The NIR spectrometer used double transmission measurements and was limited mainly to analysis of the signal produced at about 10,000 cm −1 by water and ethanol in the samples. The Raman measurements, produced using a 785 nm laser, were based on a sharp signal from ethanol at 880 cm −1. A multivariate calibration model, based on a combined PCA–PLS algorithm, was required for analysis by NIR spectrometry, whereas a univariate calibration model was suitable for Raman spectrometry. Both techniques were limited to measurements in clear glass bottles as strong absorption/fluorescence occurred with coloured glass bottles. Bottle-to-bottle variations contributed the largest uncertainty to the measurements obtained for a 20% (v/v) ethanol solution in flat bottles: 2.3% R.S.D. for NIR spectrometry and 2.2% R.S.D. for Raman spectrometry. For 700 mL round bottles, which have stricter manufacturing tolerances on glass thickness, the bottle-to-bottle variability for Raman spectrometry was 1.4% R.S.D. When spirit samples with ethanol concentrations in the range 19.9–61.7% (v/v) were analysed, the precision (average R.S.D.) was 0.4 and 0.5% for NIR (flat bottles) and Raman (round bottles) spectrometries, respectively, and the average accuracy was 2.1 and 2.9%, respectively. When a calibration model constructed from NIR data acquired on 1 day was applied to data sets collected over a 15-day period, the average error was 3.9%.

Electrospray ionization mass spectrometry fingerprinting of whisky: immediate proof of origin and authenticity

Authentic samples of whisky produced in Scotland and USA and counterfeit whisky samples commercialized in Brazil have been directly submitted to electrospray ionization mass spectrometry (ESI-MS) analysis in both the negative and positive ion modes to assess the potential of this technique for simple and rapid quality control and proof of authenticity of whisky samples. ESI in the negative ion mode yields the most characteristic whisky fingerprinting mass spectra in just a few seconds by direct infusion of the samples, detecting the most polar or acidic components of each sample in their deprotonated anionic forms. No pre-treatment of the sample, such as extraction or derivatization or even dilution, is required. The analysis of the ESI(-)-MS data both by simple visual inspection but more particularly by chemometric data treatment enables separation of the whisky samples into three unequivocally distinct groups: Scotch, American and counterfeit whisky, whereas single malt and blended Scotch whiskies are also distinguished to some extent. As indicated by ESI-MS/MS analysis, the diagnostic anions are simple sugars, disaccharides and phenolic compounds. Direct infusion ESI-MS therefore provides immediate chemical fingerprinting of whisky samples for type, origin and quality control, as demonstrated herein for American, Scottish and counterfeit samples, whereas ESI-MS/MS analysis of diagnostic ions adds a second dimension of fingerprinting characterization when improved selectivity is desired.

Solute effects on the interaction between water and ethanol in aged whiskey.

The hydrogen-bonding structure of water-ethanol in whiskey was examined on the basis of (1)H NMR chemical shifts of the OH of water and ethanol. Phenolic acids and aldehydes (gallic, vanillic, and syringic acids; vanillin and syringaldehyde) exhibited their structure-making effects regardless of the presence or absence of 0.1 or 0.2 mol dm(-3) acetic acid. The OH-proton chemical shifts were measured for 32 malt whiskey samples of a distillery, aged for 0-23 years in five different types of casks. The OH-proton chemical shift values of the whiskies shifted toward the lower field in proportion to their contents of total phenols. It can be concluded that the strength of the hydrogen bonding in aged whiskies is directly predominated by acidic and phenolic components gained in oak wood casks and not dependent on just the aging time.

Comparison of methods of analysis of time-intensity data: application to Scotch malt whisky

Time-intensity (TI) data typically consist of assessments at 1 s intervals of a set of samples by a panel of assessors. Some means of summarising the data must be found, and the data must be represented in a way which allows comparisons between samples. Parameters such as maximum intensity, time to maximum, and total duration are typically used and samples compared by analysis of variance. Thirteen assessors scored sweet taste intensity for 60 s, for 20 whisky samples drawn from 5 types of cask after 4 maturation times. Scaling and then averaging of the transformed data provided the best summary, and ante-dependence modelling showed that the intensity value at each time-point of the curve was dependent on the previous five time-points. Small effects of cask type and maturation time were found on sweet taste in whisky samples.

Gas chromatographic organic acid profiling analysis of brandies and whiskeys for pattern recognition analysis.

An efficient gas chromatographic profiling and pattern recognition method is described for brandy and whiskey samples according to their organic acid contents. It involves solid-phase extraction of organic acids using Chromosorb P with subsequent conversion to stable tert-butyldimethylsilyl derivatives for the direct analysis by capillary column gas chromatography and gas chromatography-mass spectrometry. A total of 12 organic acids were reproducibly identified in liquor samples (1 mL). When the GC profiles were simplified to their retention index spectra, characteristic patterns were obtained for each liquor sample as well as for each group average. Stepwise discriminant analysis provided star symbols characteristic for each liquor sample and group average. As expected, canonical discriminant analysis correctly classified 23 liquor samples studied into two groups of either brandy or whiskey.

Investigation into the use of carbon isotope ratios ( 13C/ 12C) of Scotch whisky congeners to establish brand authenticity using gas chromatography-combustion-isotope ratio mass spectrometry

Volatile congeners of whisky have been analysed by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Acetaldehyde, ethyl acetate, n-propanol, isobutanol and amyl alcohol from a popular blended whisky have been separated using established GC conditions and their δ 13C%. values determined. Eight samples of the whisky blend taken over the last 2 years of production have been analysed to allow the authentic range to be determined. A radar diagram has been used to graphically represent the δ 13C%. data. This was used as a simple means of comparing the carbon isotope profiles of whiskies. Two other whisky samples were analysed and shown to differ from the whisky blend on the basis of the δ 13C values.

Anodic stripping voltammetric determination of Zn, Pb and Cu traces in whisky samples

The simultaneous “in natura” determination of trace Zn, Pb and Cu in whisky samples by anodic stripping voltammetry (ASV), using a hanging mercury drop electrode, without previous treatment or addition of supporting electrolyte is described. The choice of an appropriate stripping voltammetric method and deposition potential minimizes the influence of the organic content and ensures a good reproducibility of the measurements. The reliability of the method was tested comparing the results with those of atomic absorption spectroscopy (AAS), with differences of about 10%. The method allows the determination of heavy metal ions in the μg L–1 range.

Derivative Fourier transform infrared spectrometric determination of ethanol in alcoholic beverages

A derivative Fourier transform infrared (FT-TR) spectrometric procedure was developed for the direct determination of ethanol in alcoholic beverages, from beers to spirit samples. The method is based on first-order derivative FT-IR measurements between the peak at 1052 cm −1 and the valley at 1040 cm −1, which are present in aqueous solutions and alcoholic beverages, by using a micro flow transmittance cell with ZnSe windows and a spacer of 0.029 mm. The method involves the accumulation of ten scans and provides accurate results in the determination of ethanol in alcoholic beverages without requiring any previous chemical treatment of the sample or a previous separation or extraction step. The limit of detection corresponds to 0.025% (v/v) and results obtained in the analysis of real samples of beer, wine, vodka, gin and whisky agree with those found by different reference procedures. For the determination of ethanol in beverages containing high concentrations of sugars, it is necessary previously to determine the sugar content by measuring the derivative value between 1164 and 1147 cm −1 and subsequently to correct the negative interference of sugars on the determination of ethanol between 1052 and 1040 cm −1.

Application of the statistical multivariate analysis to the differentiation of whiskies of different brands

A study was made to test the authenticity of whisky that is offered from opened bottles in Spanish public establishments. It is based on 100 genuine Scotch whisky samples from five labels and 38 genuine Spanish whisky samples of high quality; two standard populations were formed. The major volatile components and absorbances were determined from all samples. Principal Component and Stepwise Discriminant Analysis are used in the statistical treatment applied to these data to determine the differences between the Spanish whiskies and the Scotch whiskies. Also analyzed were 113 samples from bottles of Scotch whisky with one of the five standard labels, already opened in the establishment inspected. A method for identifying outliers was applied to these 113 test samples, and the contents of 41% of the bottles agreed with the characteristics of their labels, but 28% of the Scotch whiskies had been substituted by Spanish whiskies of similar quality.

Application of several statistical classification techniques to the differentiation of whisky brands

AbstractSeveral supervised (stepwise discriminant analysis (SDA), statistical isolinear multi category analysis (SIMCA) and nearest neighbour analysis (KNN)) and unsupervised (principal components analysis (PCA) and cluster analysis (CA)) classification techniques have been applied to analytical data from different whisky samples in order to distinguish between genuine whisky of a well known and expensive brand and other less expensive whiskies that could be used to replace the original contents of the bottle.

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.

Spectrophotometric Determination of Color Intensity of Whisky: Collaborative Study

Abstract A method for measuring color intensity of whisky was developed to replace the present AOAC method, which has become obsolete. The new method was collaboratively studied by 20 persons. Color intensity of whisky was measured as absorbance by a spectrophotometer, using a 1 cm cell, a bandwidth ≤10 nm, and a wavelength of 525 nm. Water was used as reference. Collaborator results appear acceptable for whisky samples that vary in color intensity from 29 to 374 CIU (absorbance X 1000 = Color Intensity Units (CIU)). The maximum standard deviation and coefficient of variation were 5.8 CIU and 6.68%, respectively. The method has been adopted official first action.

Collaborative Study of the Quantitative Gas-Liquid Chromatographic Determination of Fusel Oil and Other Components in Whisky

Abstract Fifteen chemists participated in a collaborative study for the quantitative pas-liquid chromatographic determination of the individual fusel alcohols and ethyl acetate in whisky. Two levels of congeners represented by 4 coded samples of whisky were analyzed by using t h e proposed method, employing a glycerol-1,2,6-hexanetriol column, and the official AOAC method, 9.063-9.065. Since isobutyl and the atnyl alcohols comprise by far the greatest part of fusel oil, their determination is of major importance to the total fusel oil content . Statistical analyses show that the proposed method is superior to the AOAC method for the determination of these alcohols, whereas the official method is superior for the determination of ethyl acetate and n-propyl alcohol. In general, collaborators employing modern instrumentation preferred the proposed method over the AOAC method. The former method also separates and permits the quantitative measurement of active amyl and isoamyl alcohols. The proposed method has been adopted as official first action as an alternative to 9.063–9.065 for the determination of higher alcohols and ethyl acetate in whisky.