Experimental Whisky Fermentations: Influence of Wort Pretreatments

Abstract

In addition to ethanol yield, the production of flavour congeners during fermentation is a major consideration for Scotch whisky producers. Experimental whisky fermentations can provide useful information to the industry, and this is the focus of this paper. This study investigated the impact of wort pretreatments (boiled, autoclaved, filtered) on fermentation performance and flavour development in Scotch whisky distillates as an alternative to freezing wort for storage. Our study showed that no significant sensorial differences were detected in low wines (first distillates), while the chemical compositions showed clear changes in increased levels of esters and higher alcohols in boiled and autoclaved wort. In contrast, filtered wort comprised overall lower levels of congeners. Regarding alcohol yield, all three pretreatments resulted in decreased yields. In practice, the pretreatment of wort prior to fermentation requires additional process operations, while freezing requires large storage units. The pretreatments adopted in this study significantly influence the composition of the malt wort used for experimental whisky fermentations, and this results in a poorer fermentation performance compared with untreated wort. We recommend the use of fresh or frozen wort as the best options for small-scale fermentation trials.

The potential for Scotch Malt Whisky flavour diversification by yeast

“…This finding will support the development of new yeast strains by reducing the time needed for sample preparation by eliminating the need for a double distillation for early yeast screening rounds (Daute et al 2023 ). Together with the finding that congener profiling of wort by gas chromatography–mass spectrometry (GC–MS) gives comparable data to the sensory evaluation, this could further reduce the time by not requiring a sensorial evaluation of samples in early screening steps (Daute et al 2021b ).…”

Sources of Volatile Aromatic Congeners in Whiskey

“…Yeast fermentation is arguably the most important stage in whiskey production as it produces ethanol. However, the importance of fermentation with regard to the flavor of whiskey cannot be underestimated, as it is responsible for the production of a large number of metabolites, some of which end up as congeners or as substrates for congener formation [11,54]. Different yeast strains and various mixes, fermenter design, aeration, duration, wort composition, and the presence of contaminating bacteria are all factors that can affect the congener profile [29,39].…”

“…The difference in congener profiles between different species and within individual yeast strains is dependent on the metabolism of amino acids and proteins, sugars, and the autolysis (self-digestion) of the yeast [56]. Studies investigating the effect of different yeast strains on new-make spirits demonstrated variation in congener profiles, especially in relation to ester profiles [1,54,57,58]. Special strains of distilling yeast have been developed that can tolerate high alcohol contents [59].…”

Chinese Baijiu and Whisky: Research Reservoirs for Flavor and Functional Food

“…As is known, yeastderived aroma profiles are species/strain-dependent, and therefore, each distillery possess their unique yeast selections to produce whiskies of individual styles. The application of "non-conventional" yeasts, mainly non-Saccharomyces yeasts, which is a common practice in winemaking, is gradually attracting attention, and distinctive flavors are obtained for these trials [10,11]. In addition, since boiling is absent prior to fermentation, the non-sterile environments after wort production enable the presence of diverse local microflora, such as lactic acid bacteria (LAB).…”