A Brief History of Whiskey Adulteration and the Role of Spectroscopy Combined With Chemometrics in the Detection of Modern Whiskey Fraud

Food fraud and adulteration is a major concern in terms of economic and public health. 15 Multivariate methods combined with spectroscopic techniques have shown promise as a novel 16 analytical strategy for addressing issues related to food fraud that cannot be solved by the analysis 17 of one variable, particularly in complex matrices such distilled beverages. This review describes 18 and discusses different aspects of whisky production, and recent developments of laboratory, in 19 field and high throughput analysis. In particular, recent applications detailing the use of 20 vibrational spectroscopy techniques combined with data analytical methods used to not only 21 distinguish between brand and origin of whisky but to also detect adulteration are presented. 22


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Whisky is a distilled alcoholic beverage produced from fermented grain mash where various 27 grains are used for different varieties (e.g. barley, corn, rye, and wheat). This alcoholic beverage is 28 generally classified by their country of origin, the nature of the grain, storage conditions and the type 29 of blends. The production of this type of alcoholic beverages was first reported in Ireland in the

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Irish whisky on the other hand is produced from either malted barley or a mixture of malted 72 and un-malted other cereals and barley of which a minimum of 25% must consist of malted barley.

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The combination of the use of partially malted barley and a specialised processing approach. This 74 involves the drying of the malt in closed kilns rather than over open peat fires and the application of 75 a triple distillation process, the first of which produces 'low wines' a pot still distillate, which is re-76 distilled in another pot still to produce 'feints', before being placed in a Coffey still for the final 77 distillation. It is this production process that gives Irish whiskeys their smooth and natural flavour.

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American whisky developed under an alternative legislative framework [9,11,12], US whisky 80 is broadly defined as the distillate of a fermented grain mash at less than 95% alcohol. Consequently,

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US whisky consist of a broader range of distinct products in comparison to the Irish and Scotch spirits.

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There are six major types, rye, rye malt, pure malt, wheat, Bourbon and corn, all of which are 83 produced from a different type of cereal grain. The exact type of grain and its required percentage 84 (not less than 51%) in the mash used to produce the whiskey product are governed by Title 27 of the 85 U.S. Code of Federal Regulations [11,12]. All US whisky must also conform to additional standards 86 outlined by title 27 of the U.S. Code of Federal Regulations, and so they must be distilled to not 87 more than 80% alcohol by volume, to ensure the proper flavour profile; producers are prohibited 88 from adding any colourings, caramel or flavour additives and finally, all of these whiskies (with the 89 exception of corn whisky) must be aged in charred new oak container. There is no minimum period 90 of aging specified, which creates opportunities for distilleries to differentiate their product based on 91 the aging process. One such distinction is a 'straight whisky'. For a given whisky to be designated 92 thus, it should not be blended with any other spirit, be no more than 80% alcohol by volume and 93 aged for a minimum of two years [2,11,12]. There are several other types of American whisky,

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Light Whisky (one which has been distilled at greater than 80% alcohol by volume) and Spirit Whisky

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(where a 'neutral spirit', a non-flavoured alcohol of 95% is mixed with at least 5 percent of a 97 particular type of whisky).

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Commercial distilleries began producing scotch in the late 18th century, despite its first being 99 recorded in the 1492 Exchequer Rolls of Scotland. As of 2018, the Scottish Parliament recognised 245 100 distilling related businesses. The Distillers Company (DCL) is a dominant player in the industry 101 since the "Big Amalgamation" the merger of the 'Big Five' brewing houses Buchanan, Dewar, Walker, 102 Haig, and Mackie in 1925 [6-8, 12, 13].

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American Whisky was first produced in the states of Virginia, Maryland and Pennsylvania in 104 eastern United States around late 18 th century and was originally a predominately rye-based spirit.

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Early distillers were often farmers who produced and distributed whiskey as a supplementary 106 income. In 1791, Alexander Hamilton, the U.S. Secretary of the Treasury, in an effort to generate 107 revenue, established a 25% tax on whiskey distillers. The majority of distillers operated small 108 production facilities and the federal tax was greatly opposed. This opposition became known as "The

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Whisky Rebellion" when it was necessary for the federal government to send troops to enforce the 110 tax [14]. This resulted in a larger number of producers relocating West, most notably to Kentucky.

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Over time, the number of states producing whiskey increased, including Tennessee which produced 112 the famous Jack Daniel's brand. America's whisky industry suffered repeated setbacks, including a 113 13-year Prohibition on alcohol between 1922 and 1933, which barred production of all alcohol; the 114 supporters of prohibition saw alcohol as a major catalyst for the ills experienced in the society. By the 115 1933, however, it became apparent that prohibition was going to remain a noble experiment. The 116 popularity of whiskey grew reaching its heyday in the 1950s in the U.S. before falling out of favour.

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Today, whisky popularity is resurging as established brands such as Jack Daniel's and Jim Beam offer 118 single-barrel whisky aimed at connoisseurs and new distilleries are appearing annually [11,14,15]. and the fledgling Irish State's economic policies debilitated the industry. Arguably however, far 126 more devastating was the reluctance of Irish whisky producers to adopt and capitalise on the 127 invention of the column still, which allowed for the easier production of palatable spirits which 128 Scottish distillers producing whisky blends incorporated readily. This ultimately handed an 129 overwhelming advantage to Scottish whisky producers [16,17]

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The global whisky market size was valued at USD $57.96 billion in 2018 and it is projected to 136 reach USD $89.60 billion by 2025. This growth is driven by multiple factors, including, 137 increasing disposable income, consumer preferences and changing lifestyles [15,[18][19][20]

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In 2018, the US spirits industry gained market share over beer and wine, with sales rising seven-142 tenths of a point to 37.4% of the total beverage alcohol market. This was the ninth straight year of 143 record spirits sales and volumes, reflecting continued market share gains. Supplier sales were up 144 over 5.1%, rising from USD $1.3 billion to a total of USD $27.5 billion [20].

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In 2019, Ireland's total agri-food sector exports amounted to €14.5 billon, with the food and

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Brand recognition is central to whisky global market growth, following a trend of 'drink less but

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Consequently, fraud, particularly in the distilling sector is causing increasing levels of concern.
198 It is an incredibly lucrative business, with perpetrators profiteering at comparatively lower risk as 199 the legal repercussions are much more lenient than those for other illegal activities, such as drug 200 trafficking [21-23, 30, 35, 43, 44]. It is apparent that without a proper verification technique that 201 derives from the beverage itself rather than some externally affixed marker or associated paperwork 202 (e.g. blockchain), the system will always be vulnerable to the inclusion of illegal or otherwise non-203 compliant material [45][46][47][48].

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In order to assess the composition and identity of the beverage directly, the development of 205 rapid and non-destructive analysis methods are critical for the future of the whisky industry. In 206 addition, methods to verify the compliance of producer declarations regarding origin and source, as 207 defined and requested by quality assurance standards in the production value chain will be of benefit.      [65]. Consequently, analysts will often apply a work around, which might include the addition of a 280 component to interact with the adulterant you wish to identify so that its response can be well 281 separated out and measured. However, the majority of spectroscopic 'fixes' or sample pre-treatments,

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to aid in the extraction of results from the spectral data work less well than is ideal. That being said,

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there is a considerable wealth of "information" gathered in a spectral scan that is not used for 284 identification or measurement. Scientists have begun to look at this unused data to determine if 285 some data points can be used to elicit different patterns that could be used to verify the measurements 286 of similar species better and without the need for a second type of confirmation test to be conducted.

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This type of forensic investigation of all of the spectral data is commonly referred to as a chemometric The combination of scientific analysis with software tools underpinned by mathematical systems 295 is of enormous use to those companies trying to track fraudulent products. It is timely now that as 296 the number of whisky producers is on the increase that adulterant measurement and analysis has 297 become more robust. The integration of chemometrics with spectroscopy allows the analyst to better 298 mine the data and extract relevant information for the generation of more confidence in a specific 299 result. While chemometric software can certainly add more certainty to analysis results it is still 300 challenging where one is trying to measure whether a single or small amount of an adulterant is 301 present or not in a sample that already has many components present natural. Food and beverages

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are examples of such complex samples, and the data may have to be analysed at different spectral 303 wavelengths or channels to be of use. The data generated often has a high number of correlations 304 from one measurement channel to the next and from one chemical species to the next over those same 305 channels. This high serial correlation decreases the use of much the data and this can be a limiting 306 factor. However, all is not lost, as the data results can be refined using chemometric software to allow 307 for such redundancy of data. Nowadays, spectroscopic instruments have inbuilt chemometric 308 methods which are extremely efficient at extracting unique and redundant information from 309 multichannel data such as spectra [61][62][63][64].

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The field of chemometrics is still evolving and consequently it defintion requires continued 311 modification to allow for its development, the international chemometrics society defines 312 chemometrics as the chemical discipline that exploits mathematical and statistical methods to design 313 or select optimal measurement procedures and experiments to provide maximum chemical 314 information by analysing chemical data [62].

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For example, it is very hard to find a wavelength channel in a standard UV -Vis spectrum to 316 distinguish between alanine and glycine, both essential amino acids in foodstuffs, as chemically they 317 are very similar, and both tend to absorb over the same sets of wavelengths. However, because 318 chemometrics expects this correlation, it allows the analyst to take advantage of the correlations 319 similarity or redundancy to increase the methods precision, similar to the manner that a mean takes 320 advantage of the redundancy of a set of numbers. This is referred to as multivariate analysis.

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The recent literature presents a number of spectroscopic techniques for the rapid and more 323 reliable identification of adulterants in whisky (Table 32)  field-testing. The spectroscopic method was also quicker (i.e., sample could be analysed in less than 339 a minute compared to a GC analysis time of approximately 20 minutes), was more cost and resource 340 effective when in compared to the standard methods [69].

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Martins and co-workers [70], determined that UV -Vis spectroscopy combined with partial least

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Recently work by Ellis et al [79,80], has investigated the use of Raman spectroscopy combined 411 with chemometrics as a means for rapid in situ through-container analysis of whisky samples; the 412 authors report detection of multiple chemical markers known for their use in the adulteration and 413 counterfeiting of Scotch whisky, and other spirit drinks without any physical contact with the sample;

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with the ability to discriminate between and within multiple well-known Scotch whisky brands, and 415 the detection of methanol concentrations well below the maximum human tolerable level of 2% v/v.

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The implementation and adoption of spectroscopy techniques combined with chemometrics 418 allows for the rapid and non-destructive analysis, characterisation and detection of fraud in whiskies.

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The most promising and significant developments point to the use of NIR, MIR and Raman 420 spectroscopies combined with data mining tools as the means for analysis of fraudulent whisky and 421 related beverages, giving greater confidence in quality evaluation and adulterant analysis. It has 422 been also demonstrated by several authors that both the accuracy and robustness of the methods 423 described are comparable to those obtained by traditional analytical tools such as GC-MS techniques.

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The field of study however is still in its early stages and it should be noted that the application of 425 calibration models requires continuous validation and as it is the critical step to ensure the robustness 426 of the method.