Investigations into the Use of Copper and Other Metals as Indicators for the Authenticity of Scotch Whiskies

Abstract

Trace element analyses were conducted on 35 Scotch Whiskies to investigate if the trace element fingerprint is characteristic for different kinds of Scotch Whiskies. The element concentrations of the eight elements investigated varied considerably; for zinc and iron three orders of magnitude (0.02 to 20 mg Zn L -1 and 0.02 to 28 mg Fe L -1 ), while nickel and magnesium varied within two orders of magnitude (0.002 to 0.6 mg Ni L -1 and 0.02 to 4 mg Mg L -1 ). Small variations were detected for calcium, sodium and copper (0.5 to 4 mg Ca L -1 , 2 to 24 mg Na L -1 , 0.1 to 1.7 mg Cu L -1 ), while lead, with one exception was usually below 0.005 mg L -1 . Using Cluster analysis no characteristic metal fingerprints were identified for the different geographical regions. However, when a second set of samples (42 malt and 8 blend whiskies) were analysed for copper, the copper concentration could be used as a criterion to distinguish Blended or Grain Scotch from Malt Whisky. The Malt Whiskies had a copper concentration between 385 and 480 ng mL -1 (95% confidence limit) while the copper concentration of the blended whiskies was between 143 and 242 ng L -1 . Since the difference was highly significant (p < 0.0001), it is suggested that a simple copper analysis could be used as one test to distinguish between a Blended and Malt Scotch Whisky.

Elemental Profiles of Whisk(e)y Allow Differentiation by Type and Region

“…Mean recoveries ± RSD ranged from 65% ± 17% for Ba to 121% ± 26% for Pt for the elements monitored by ICP-MS, while recoveries for the five elements monitored by MP-AES were between 102% ± 1% (Ca) and 117% ± 4% (K). Similar recoveries were reported previously for copper (98% [13]; 101.6% [12]) and several other elements (Be, V, Cr, Mn, Fe, Co, Ni, Zn, As, Se, Cd, Sn, Sb, Ba, Hg, Pb, U; between 97.3% and 107.5% [12]), using graphite furnace-atomic absorption spectroscopy (GF-AAS) [13] and ICP-MS [12].…”

“…Three elements, Cu, Sr, and V, showed large significant differences between the five production areas: Similar to Adam et al [13], copper levels differed significantly among the five production areas, with highest Cu levels in samples from Speyside (n = 9; 5 distilleries) and Island (n = 6; 4 distilleries), and significantly lower levels in samples from Highland (n = 7; 5 distilleries). Intermediate levels of Copper were measured in samples from Islay (n = 6; 5 distilleries) and Lowland (n = 4; 2 distilleries).…”

“…Nickel and zinc are common alloy elements for copper [46], a fact that is substantiated by significant positive correlations to copper for the studied samples (Ni: r(66) = 0.43, p < 0.001; Zn: r(66) = 0.42, p < 0.001). Calcium levels were shown to vary in Scotch whiskies [13], possibly either leaching from barrels over time or originating from water used in the dilution process. Positive correlations between Ca and Mg (r(66) = 0.63, p < 0.001), and Ca and Na (r(66) = 0.43, p < 0.001) in our data indicate that the most likely origin of these elements is the water used in diluting the whisk(e)y to the desired strength, either right after distillation or before bottling [47].…”

“…Nevertheless, stainless steel stills are also used in whisk(e)y production, e.g., in combination with subsequent copper columns or copper mesh inside the stainless steel still [44]. Copper levels were shown to vary based on the size of stills, with malted scotch whiskies made in small scale pot stills having higher amounts of copper than blended and grain whiskies from Scotland [13]. In general, most of the copper in whisk(e)y is thought to come from processing equipment compared to raw materials [45].…”

The perceptual categorisation of blended and single malt Scotch whiskies

“…(e.g. [2]; see [16] for a review). None of this guarantees, however, that the distinction between single malts and blended scotch is perceptually salient and readily detectable by whisky drinkers.…”