Why do distilleries all the world over spare neither trouble nor expense just to have their distillates stored for years in special casks made of White Oak? This certainly can not be explained by tradition alone. But why is it then that distilleries do not make do with wood chips, which are commonly used in the production of cheap red wine? The previous articles on cask maturation published here on Liquorpress have shown that the distillate contains more flavour-carrying substances if the contact area between wood and alcohol is larger, as is the case with quarter casks (see part 1 and part 2). So why not just use oak chips instead of oak casks and get the maximum contact – and thus extraction – surface? To detect the differences between storage using wood casks and wood chips, experiments were conducted in suitable laboratories in the context of a research paper. (Image: Bob Shenk/FlickR)

This project aims to recreate in principle and observe the processes during a spirit’s ageing and storage, using modest means. Using wood chips, the distillate, Irish Knockeen Hills® Poteen, aged for 84 days. This Irish distillate with an alcohol content of 90 % has not matured and may therefore not be called whisky. Wood chips that have not been treated and those that have been slightly burnt to simulate the effects of “toasted” oak casks are filled into separate sealable glass containers. Then the Irish Knockeen Hills® Poteen, diluted down to 63 % alc./vol. by adding 2 cl (0.7 fl oz) of water to 5 cl (1.7 fl oz) of the distillate, was added to each of these containers. It took only 24 hours for a distinct yellow-brown colour to manifest, which became even more intensive in the following weeks. Substances giving the distillate flavour and colour are extracted at such a fast rate due to the wood-to-alcohol rate. As the surface area of the oak chips is relatively large compared to oak casks, the lignin compounds are able to be extracted significantly faster than would be possible in casks.

The two images above clearly show the differences in the colour of the different distillates. The Glenfiddich 12 Years Old Special Reserve whisky exhibits the typical colour of a whisky that has matured for 12 year in an oak cask, whereas the raw distillate, which has not matured, is clear. The whisky sample matured in untreated wood chips has a more intensive and reddish colour than the Glenfiddich sample, which is due to the larger surface area of the wood chips. The sample that was matured in toasted oak chips has the darkest colour, caused both by a greater extent of extraction – cracks in the wood increase the surface area – and also by soot and coal particles dissolved in the liquid. Unsurprisingly, the taste of the whiskies matured in this manner could not hold up to that of professionally produced whiskies. Admittedly, both test samples displayed a kind of fruity flavour and were distinctly different from the non-matured distillate, but their aromas were very “thin”.

Related posts:

1. The chemistry of casks – Part 2
2. The chemistry of casks – Part 1
3. Influence of nature on taste and aroma