The influence of alcohol content variation in UK packaged beers on the uncertainty of calculations using the Widmark equation

Abstract

It is common for forensic practitioners to calculate an individual's likely blood alcohol concentration following the consumption of alcoholic beverage(s) for legal purposes, such as in driving under the influence (DUI) cases. It is important in these cases to be able to give the uncertainty of measurement on any calculated result, for this reason uncertainty data for the variables used for any calculation are required. In order to determine the uncertainty associated with the alcohol concentration of beer in the UK the alcohol concentration (%v/v) of 218 packaged beers (112 with an alcohol concentration of ≤5.5%v/v and 106 with an alcohol concentration of >5.5%v/v) were tested using an industry standard near infra-red (NIR) analyser. The range of labelled beer alcohol by volume (ABV's) tested was 3.4%v/v - 14%v/v. The beers were obtained from a range of outlets throughout the UK over a period of 12 months. The root mean square error (RMSE) was found to be ±0.43%v/v (beers with declared %ABV of ≤5.5%v/v) and ±0.53%v/v (beers with declared %ABV of >5.5%v/v) the RMSE for all beers was ±0.48%v/v. The standard deviation from the declared %ABV is larger than those previously utilised for uncertainty calculations and illustrates the importance of appropriate experimental data for use in the determination of uncertainty in forensic calculations.

Uncertainty in Widmark calculations: ABV variation in packaged versions of the most popular beers in the UK

“…Following on from this the mean difference of the measured %ABV minus labelled %ABV was found to be -0.1 %v/v, and the RSME was determined to be 0.1 %v/v, which is easily within the legally allowed limits of the Packaging Regulations and is as expected with data declared during the Molson-Coors tax tribunal [15]. This RMSE was smaller than that previously determined RSME  0.4 %v/v for 112 different craft beers (n=112) [11]. These data highlight the differences between beer from small, independent producers and national or global entities, who are likely to have a greater capacity to invest in technology to ensure that the packaged product falls within the legal limits on every occasion.…”

“…The method of analysis was adapted from Maskell et al [11] and from the American Society of Brewing Chemists [18], in brief, each beer sample upon opening was immediately de-gassed by filtering through grade A filter paper (Whatman, Maidstone UK), into 50 ml centrifuge tubes (Fisher Scientific, Loughborough, UK). Duplicate 20 ml samples were then passed through an Anton-Paar DMA 4500 density meter connected to a Beer ME Alcolyzer unit (Anton-Paar, St Albans, UK) to measure the %ABV.…”

“…These additions are therefore carefully controlled, and, in some cases may be used to the brewers' advantage [15], within the tolerances allowed by packaging legislation in the UK [16,17]. It was postulated that the ABV of these mass-produced beers, of which makes up the majority of beer sales in the UK, would have a smaller standard deviation from what is declared on the packaging when compared with a previous study of craft brewed products [11].…”

“…The variables for the individual that we used are shown in table 2. In order to determine the %CV of the amount of ethanol in an alcoholic beverage to compare the results to Gullberg (%CV = 3%) we used the standard deviation (SD) of %ABV from this study and the work of Maskell et al, [11,20] (ABV and volume). We assumed that the individual had consumed 2 UK pints (568 ml) of 4% ABV beer.…”

“…A recent study [11] determined the uncertainty for ABV that could be applied for Widmark equation calculations when considering 'craft' beers in small packaging units (bottles and cans). However, unlike in the USA, there is no definition of 'craft' in the UK [12] and this is reflected in a study of consumers which found that only 15 % of UK consumers self-identified as having consumed 'craft beer' in the previous six months [8].…”