|dc.description.abstract||Whiskey is among the oldest and one of the most consumed spirit based drinks in the world. Traditionally whiskey is aged for three or more years in wooden barrels to mature the spirit. During maturation, a variety of compounds are extracted from the wood to give a complex mixture of flavours and aromas. It is desirable to speed up the reactions which take place during maturation including, extraction of compounds from wood and reactions between the distillate and wood compounds. The benefits of ageing the spirit faster are the reduction in storage space, time and costs associated with the ageing process.
This project was carried out for a commercial company with a focus on maturing fresh distillate using different ageing techniques; heat, light, heat-freeze and sonication with wood chips to obtain the flavours and aromas associated with mature whiskies in a short timeframe. Quantitative (concentration, ppm) and qualitative (peak areas, ISTD corrected) analysis was carried out on samples stored over time using gas chromatography mass spectrometry (GC MS).
Initially, different sized wood pieces (toasted to varying degrees) were soaked in 65% ethanol, to replicate a whiskey matrix, and heated over four weeks to confirm what compounds were extracted from the wood and their relative quantities. The ethanol experiment also allowed determination of the optimal temperature (70 °C), time (≤ 14 days), wood size (small chips) and toasting level (medium toast) to extract compounds in a short timeframe with similar levels to the analysed commercial samples.
Heat, light, heat freeze and sonication treatments were separately applied to fresh distillate (corn and malt) with different wood sizes and toasting levels. Experiments were sub sampled over time. The determination of the compounds present and the effects of different treatments on the concentrations/peak areas were compared. Experiments were also compared to commercial samples (n = 51) to investigate whether a mature whiskey profile had been achieved.
Samples heated (70 °C) for six days had some desirable compounds (furfural, 1,1 diethoxyethane, several esters and several phenolic aldehydes) at concentration/peak areas similar to commercial samples. Sonication (≤ 8 hours) with medium toast small chips also produced good results for several reasons; the colour and aroma were similar to commercial samples and it had a similar compound profile to commercial samples for the analysed compounds. Furthermore, untargeted analysis using principal component analysis indicated that the corn distillate sonication samples (non-heated and 50 °C) and heat freeze (day 9) samples were clustered with the 10-12 year-old whiskey sample group whereas the heat-only samples were clustered further away. In comparison, the malt distillate samples did not cluster near any of the commercial samples. Linear discriminant analysis was used to categorise the heat, heat-freeze and sonication samples to an age group based on the model created from the analysed commercial samples with 90% predicted to have a chemical profile ≥ 10 years old (≥ 72% probability). Overall, several age treatments show promise in rapidly maturing whiskey.||