CB5 -- A Feast for Yeast: Flavor Compound Comparison Between Pacific Ale and Irish Ale Yeast Strains

The flavor and body of a beer are heavily influenced by the strain of yeast selected for fermentation. Each strain produces distinct metabolites, resulting in unique flavor profiles (Humia 2019, Olaniran et al. 2017). While two or more strains can be blended to produce novel flavor combinations, competition between the yeasts can cause inconsistency between consecutive batches. In addition, dominance by one yeast strain can dampen the impact of other strains within the blend (Humia 2019). In this study, Pacific Ale (WLP041) and Irish Pale Ale (WLP004) yeasts, purchased from White Labs in Asheville, NC, were blended in a 50:50 mixture to determine whether both yeast strains would contribute equally to the beer’s flavor compounds or whether one strain would dominate the beer’s flavor. Additionally, this study analyzed how re-pitching a 50:50 blend of Pacific Ale and Irish Pale Ale yeasts could influence yeast cell concentration and fermentation performance in subsequent batches or generations. The blended treatment groups (2nd generation and 3rd generation) and the control groups (Pacific Ale only and Irish Ale only) were used to brew different beers at a local brewery under similar conditions. Then, high performance liquid chromatography (HPLC) was run on the four samples and on an aerated wort. Using percent similarity, the three maximum peaks of the HPLC graph of the blended batches were compared to those of the controls and the aerated wort. The three peaks were also compared to the peak intensities of the controls averaged together to determine whether both yeasts were contributing equally to the beer’s flavor. Gas chromatography–mass spectrometry (GC-MS) was also used on the five samples with the aim of identifying the compounds that differ between treatment groups. The results from the HPLC chromatograms indicated that both blended batches would be better described as an equal contribution by both yeasts strains, than as a dominance by either individual yeast strain alone. However, with each generation of fermentation, the beer began to exhibit more unique characteristics of an Irish Pale Ale beer than the characteristics generally associated with the Pacifica Pale Ales. Because of the increasing differences between the blended batches and the aerated wort, the analysis also evidences that each generation of fermentation made the beer more distinct from the original wort