In a recent post I looked into the science behind the phenolic compounds found in my favorite Scottish malt whiskies, and extracted into said water of life via the action of alcohol and water on the wood of the oak barrels they are aged within. I realise this was quite neglectful of the fact that a range of other distilled spirits undergo barrel aging to produce their unique characteristics. Thankfully science has not been so negligent on this topic and a study from 1999 in the Journal of Agricultural and Food Chemistry investigated this very subject.
The graph shows the mean total antioxidant status (mmol/L) of distilled spirits analysed by Goldberg et al in their 1999 study.
This study analysed both the total antioxidant capacity and the amounts of a range of phenolic and furan compounds. This included both a single malt scotch whisky and a blended whisky, although unfortunately for comparison with my previous post they do not mention the age of this whisky. Judging from the amount of ellagic acid in the table below it could be suggested to be a 10-12 year old single malt. Of more interest here is that the study also included an American bourbon, French brandy and Armagnac. This study included a few different compounds found in barrel aged spirits. The structures of these are shown below, illustrating the complexity of compounds that develop during the aging process.
Structural formulas of the main compounds mentioned.
Looking at the graph above and table below a particularly interesting finding is that American bourbon exceeded the Scotch malt whisky in both its antioxidant capacity and levels of individual phenolic compounds. The authors suggest some reasons for this:
“Bourbon whiskey is made by rather different procedures. Two, in particular, are worthy of note. The distillation takes place at a quite low proof, not exceeding 160; this has the effect of allowing many congeners to pass over with the ethyl alcohol. The second is the use of charred oak barrels for aging, periods of up to 8 years not being uncommon. It appears that these two processes may account for the higher phenolic and furan contents and TAS of this whiskey compared with the previous three whiskies”
Perhaps also the use of freshly made oak barrels increases the transfer of phenolic compounds into bourbon, as compared to Scotch whisky which reuses previously used barrels. Vanillic Acid, Syringaldehyde were found in the highest amounts in bourbon. The lower levels identified in the Canadian rye whisky are mostly likely to a much shorter duration of barrel ageing.
The quantities of six polyphenols in the various spirits tested.
The striking feature of this study is the high amounts of all phenolic compounds in Armagnac, which had by far the highest concentrations of gallic acid, syringic acid, vanillin, and ellagic acid, as well as the second highest of vanillic acid, syringaldehyde, coniferaldehyde, and trimethoxyphenylacetic acid. This is possibly due to the exacting and protected methods used to produce Armagnac, of which wood aging of up to 10 years in Limousin oak for cognac and black Monlezun oak, a “black oak” from the Monlezun forest in Gascony, for armagnac, is a notable feature. Of interested, the ellagic acid found in both whiskies and Armagnac, is also proposed to be responsible for some of the health benefits of fruits such as blackberries, cranberries, pomegranates,raspberries, which are the main source of ellagic acid in the diet. However, the amounts in even Armagnac are rather low in comparison.
While the evidence from my previous post showed that long aged Scottish malt whisky, aged 25 years, had a much higher level of phenolic compounds than any in this study, the age of Scotch malt whisky at which most people drink it may not quite reach the levels of phenolics found in American bourbon, and is probably rather inferior to Armagnac. As the phenolic compounds extracted from oak wood during the aging of alcohol are common to all aged spirits, any health effects mentioned in my previous post would apply to all. However, it is worth remembering any possible health benefit is going to be redundant if consumed in large quantities.
*Any spelling mistakes in the post are due to the influence of good whisky.
Goldberg DM, Hoffman B, Yang J, Soleas GJ. (1999) Phenolic constituents, furans, and total antioxidant status of distilled spirits. Journal of Agricultural and Food Chemistry. 47(10):3978-85
“The concentrations of 11 phenols and 5 furans were measured in 12 categories of distilled spirits by HPLC methodology, together with the total antioxidant status (TAS) of the same beverages. Ellagic acid was the phenol present in highest concentration in all beverages. Moderate amounts of syringaldehyde, syringic acid, and gallic acid, as well as lesser amounts of vanillin and vanillic acid, were measurable in most samples of whiskey, brandy, and rum but were largely undetectable in gin, vodka, liqueurs, and miscellaneous spirits. 5-(Hydroxymethyl)furfural was the predominant furan in the former three beverages, notably cognac, with 2-furaldehyde the next highest, but these were undetectable in most of the latter beverages. Highest TAS values were given by armagnac, cognac, and bourbon whiskey, all three of which tended toward the highest concentrations of phenols. Negative TAS values were exhibited by rum, vodka, gin, and miscellaneous spirits in line with the low or undetectable phenol concentrations in these beverages. Wood aging is the most likely source of phenols and furans in distilled spirits. Those beverages exposed to this treatment contain significant antioxidant activity, which is between the ranges for white and red wines, with the potential to augment the antiatherosclerotic functions attributable to the ethanol that they contain.”