Investigating the Impact of Acetaldehyde Accumulation on Beer Quality: Metabolic Pathways, Yeast Health, and Mitigation Strategies
Magezi Edgar and Ampaire Wycliffe
ABSTRACT
Acetaldehyde is the immediate precursor to ethanol in fermentation. Like diacetyl, acetaldehyde is found in large quantities during early fermentation as the yeast produces it early in its metabolic cycle. If there is a high amount of dissolved oxygen present in the young beer, then the oxygen could react with ethanol and oxidize it back into acetaldehyde. The content of acetaldehyde in beer varies from 1 to 20 mg/L depending on many processing factors. Higher concentrations of this metabolite not only induce unpleasant “young” or “green” off-tastes but also participate with phenolics in the formation of beer haze. Acetaldehyde is present in all beers and, in lower concentrations, can contribute positively to a beer’s sensory character. When the concentration of acetaldehyde remains above or well above its sensory threshold, it becomes an off flavour. The concentration of acetaldehyde is tied to yeast health and is formed during the beginning and middle of beer fermentation. Its concentration will normally decrease towards the end of a healthy fermentation and maturation process. Acetaldehyde can rise during prolonged warm maturation when yeast loses viability. Typical sensory descriptors associated with acetaldehyde include green (Granny Smith) apples, pumpkin flesh/seed, unripe avocado, and latex paint. Acetaldehyde is somewhat unique in this regard; the “character” of its aroma can change as its concentration changes. The sensory threshold in pale lager beer is typically 1-5 mg/L but this can vary with beer style, in some cases ranging from 5 – 15 mg/L. Acetaldehyde is formed by all yeast. As yeast undergoes fermentation, glucose is turned into pyruvate and then acetaldehyde, and finally ethanol. Yeast utilizes this metabolic pathway of glycolysis to maintain levels of ATP, adenosine triphosphate, aka the energy currency of the cell. From the study entitled investigating the possible causes of the high levels of acetaldehyde off flavour in beer during fermentation in cellars about the suspected Aber system inconsistency, the obtained results portrayed a very abnormal acetaldehyde production level. Three samples were studied for each brand and it was observed that all showed higher acetaldehyde level diversion. For NLS, all the samples studied were found to have acetaldehyde levels of 24.07, 22.01, and 20.87 ppb against the expected maximum levels of 10 ppb. For CPL, the levels were at 24.05, 20.00, 23.50, and finally 25.04, 26.24, and 27.01 for all the ELX brands.
Keywords: Acetaldehyde; Off-flavour; Yeast pitching efficiency; Fermentation tanks; Nile Breweries
CITE AS: Magezi Edgar and Ampaire Wycliffe (2024). Investigating the Impact of Acetaldehyde Accumulation on Beer Quality: Metabolic Pathways, Yeast Health, and Mitigation Strategies. IAA Journal of Scientific Research 11(2):40-51. https://doi.org/10.59298/IAAJSR/2024/112.4051