THE FATE OF THE SULPHUR CONTENT OF MALATHION WHEN APPLIED TO BARLEY USED TO PRODUCE MALT WHISKY

The use of malathion to protect malting barley from infestation by insects led to fears that malt whisky could be tainted by odorous sulphur compounds such as mercaptans derived from the malathion. Laboratory scale experiments in which barley was treated with sulphur-35 radio-labelled malathion, showed that the majority of the sulphur from the malathion was lost in the early stages of processing and that none penetrated to the final distilled spirit. Treatment of malt with the radio-labelled malathion showed that although the majority of the sulphur from the malathion was lost after the infusion and fermentation stages, a small percentage was found in the distilled spirit. However, re-use of the final infusion liquor as the first liquor on the next batch of malt as is common practice, could lead to a slight risk of an accumulation of sulphur compounds until equilibrium is reached.     

IDENTIFICATION OF LACTIC ACID BACTERIA ISOLATED FROM DIFFERENT STAGES OF MALT WHISKY DISTILLERY FERMENTATIONS

A number of strains of lactic acid bacteria were isolated and identified from samples obtained from different stages of malt whisky distillery fermentations. Isolates were subjected to a range of biochemical and physiological tests and results obtained were used to make tentative identifications. The types of lactic acid bacteria associated with a particular stage of the fermentation are discussed. Results obtained suggest that Leuconostoc was the most common bacterial contaminant and tends to die off at the later stages of the fermentation. The most likely sources of bacterial contamination in the distillery are discussed. Results have shown that yeast is a very important source of contamination on an industrial scale.     

The influence of malt and wort processing on spirit character: the lost styles of Scotch malt whisky

Over the last 50 years there has been considerable analytical research on the malt parameters which govern the flavour and aroma, i.e. the ‘character’, of Scotch malt whisky. This has led to a standard format, the Flavour Wheel, to describe the attributes of any malt spirit and to relate them to a common group of malt parameters. What has not been well documented in the same period are the changes in malt processing technology which have led to a gradual but significant change in the concentrations of reference compounds used in the Flavour Wheel relating to sulphury, nutty/burnt/smoky, peaty and fruity/estery characters. This review covers the most significant of these changes, which have become common practice across the industry, and specifically demonstrates how different malting barley varieties, malt kilning and peating, wort recovery, yeast management, and wash still heating have all contributed to the loss of some styles of malt whisky. © 2019 The Institute of Brewing & Distilling     

The Impact of Copper in Different Parts of Malt Whisky Pot Stills on New Make Spirit Composition and Aroma

In Scotch malt whisky production, the use of copper for the construction of the pot stills for distillation is regarded as having an important effect on whisky aroma. During distillation in copper pot stills, the copper acts to reduce sulphury aromas in the resultant spirit by reducing the levels of sulphur compounds such as dimethyl trisulphide (DMTS). This work has shown that the copper is more effective in this role in some parts of the pot stills than others. This information can be used to help distillers maintain or, indeed, to alter new make spirit aroma. It was also noted that in addition to DMTS, other, as yet unidentified, compounds make a significant contribution to sulphury aromas, so future research efforts should focus on identifying such compounds.     

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.     

Influence of Zinc on Distiller's Yeast: Cellular Accumulation of Zinc and Impact on Spirit Congeners

Accumulation of zinc by a whisky distilling yeast strain of Saccharomyces cerevisiae was studied during fermentation of malt wort and synthetic defined medium. Zinc uptake by yeast cells was very rapid in malt wort, as zinc (0.32 μg/mL) was completely removed from the fermentation medium within one hour. The type of fermentable carbohydrate had an impact on the kinetics of zinc accumulation, with maltose most effective at enhancing metal uptake at zinc concentrations above 3.2 μg/mL. Enriching yeast cells with zinc by “preconditioning” impacted on the production of flavour congeners in the distillates produced from fermented cultures. Such distillates were characterised by an altered flavour and aroma profile. In particular, the production of some higher alcohols increased when yeast cells were preconditioned with zinc. This phenomenon is yeast strain related. Industrial fermentation processes, including brewing and distilling, may benefit from optimization of zinc bioavailability in yeast cultures resulting in more efficient fermentations and improved product quality.     

ETHYL CARBAMATE FORMATION IN GRAIN SPIRITS: PART IV—RADIOCHEMICAL STUDIES

The formation of radioactive ethyl carbamate from added H¹⁴CN was studied in a sample of new spirit from a grain distillery. Reaction conditions were at ambient temperature in the dark. Cupric ions added to spirit promoted the incorporation of cyanide into ethyl carbamate.     

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.     

Optimisation and Validation of the “Strathclyde Simulated Mouth” for Beverage Flavour Research

Flavour is perceived as the result of partition and equilibrium of volatile odorants of a food during consumption. Research previously carried out with whisky has been restricted to sensory and conventional chemical analyses, which have made a contribution to understanding the process, but cannot show what happens when whisky is consumed. Dynamic headspace methods are required to take a step further into understanding the phyco‐chemical interactions that take place in the mouth of the consumer or laboratory assessor. Buccal headspace analysis has been used for whiskies, but cannot be used for model systems of non‐food materials. The “Simulated Mouth” was therefore designed and constructed to imitate the mouth. Operation of the simulated mouth was optimised using buccal headspace analysis as a reference method. Parameters that were taken into consideration were: the flow rate of hydrated air through the simulated mouth cavity, presence of artificial saliva, the size of the vessel, the amount of whisky used, the use of glass beads to simulate teeth, shaking or static condition, and the time for collection of volatiles. The simulated mouth showed systematic changes in a series of samples of different maturation times. The arrangement of the model and the methodology should also be appropriate for study of flavour release from other liquid systems.     

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.