"Evolution of organic acids during Scotch whisky fermentation".

Scotch whisky fermentations are usually carried out with a known species of Sacchromyces cerevisiae yeast, however there will usually also be a population of Lactic Acid Bacteria present in the distillery and fermentation vessels. During fermentation, hundreds of metabolites, including organic acids, are produced by these organisms which can positively or negatively contribute to final product flavour and aroma. The presence of these organic acids has been shown to impact on the flavour of distilled spirits such as Scotch malt whisky, where they are usually thought to confer positive attributes to final spirit quality.

In the work presented, high-performance liquid chromatography (HPLC) with UV-detection fitted with a reversed phase column, was used to determine how organic acids evolve during distillery fermentations. Samples were collected from a commercial distillery in Scotland following multiple fermentations. Laboratory fermentations (20 L) using a replicated distiller’s wort, were conducted to compare distillery fermentations to small scale. These fermentations were distilled on a 30 L wash still and 5 L copper alembic style spirit still to assess the organic acids in low wines and new-make spirit. As proof of the applicability of the acid detection method, laboratory scale beer fermentations using Lallemand Wildbrew™ Sour-Pitch yeast were performed along with analysis of commercial beer samples.

The results demonstrated the pattern of lactic acid formation in industrial distillery fermentation and allowed the comparison with laboratory fermentations. It was also confirmed that this technique can be used as a rapid method of organic acid detection that can be applied to whisky and brewery fermentations, as well as to final products. By monitoring levels of organic acids during fermentation this could be a valuable research tool to indicate changing conditions within fermentation vessels, which in turn could affect spirit character.