Whisky Magazine Issue 54
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Ian Wisniewski explains how oxidation affects maturation
With oak casks regarded as the key influence during maturation, it's tempting to see oxidation (the interaction of air and spirit within the cask) as a secondary factor. However, as air (principally oxygen) is an essential enabler of maturation, oxidation is actually a vital element.
But oxidation is also one of the most difficult influences to monitor and quantify, and consequently one of the least understood elements of maturation.
Oxidation is the result of the cask being porous, and able to ‘breathe' in air. As air within the cask dissolves into the spirit (oxygen being the key element), this sees esters, aldehydes and acids within the spirit continually reaching a new equilibrium. Beyond the science, this promotes a fruitier, more floral, balanced and mature spirit.
One theory is that during the early stages of maturation, oxidation can help diminish less desirable sulphur compounds (which are primarily absorbed by the layer of char within a cask, while also passing through the pores of the cask as vapours).
Moreover, a reduction in sulphur compounds, in the early stages of maturation, may help promote greater levels of oxidation, so it can be a selfperpetuating process.
As sulphur compounds feature a distinctive line-up of notes, ranging from struck match, sulphurous, rubbery, meaty and sweaty socks, to cabbage and vegetal, they can ‘conceal' other characteristics within the new make spirit.
While a certain level of sulphur character can be desirable, dependi...