Influence of Different Fermentation Conditions on the Aroma-Active Compounds During New-Make Whisky Production Determined by GC-MS, GC×GC-O-MS, HPLC, and UPLC-MS.

Whisky is well-known worldwide owing to its unique flavor, and its fermentation and distillation conditions have a significant effect on its aroma. In this paper, new-make spirits were prepared by four fermentation conditions (two distilling yeasts and two fermentation temperatures), and the different stages (wort, wash, low wine, and new-make spirit) of the samples were collected. The main aroma compounds and their precursors were initially determined in wort and wash samples by GC-MS, UPLC-MS and HPLC. Results showed that Strecker degradation, reduction, and esterification occurred during the fermentation process, leading to decreased contents of amino acids and increased contents of volatile esters, alcohols, and acids. Moreover, the two distilling yeasts exhibited their respective optimal fermentation temperatures. Then, the distillation process was evaluated by two-dimensional gas chromatography-olfactory-mass spectrometry (GC×GC-O-MS), and 74 aroma compounds were found in different stages of new-make whiskies fermented by the two distilling yeasts and one brewer's yeast. The contents of most compounds were enhanced by at least ten times after two distillations, while the contents of some sulfur compounds decreased. Finally, the feature aroma-active compounds of each new-make whisky were identified according to rOAV. These results provided theoretical and methodological support for yeast selection and process control in whisky production.