Abstract
Specialty wort systems often contain unusual sugar profiles, higher extract levels, adjunct-derived compounds, and altered nutrient balance, which can affect ale and lager yeast behaviour differently. This study compares fermentation behaviour of ale and lager yeasts in specialty wort systems. Controlled fermentations were conducted using standardized specialty wort under identical pitching rate, oxygenation, and nutrient conditions, while yeast type and fermentation temperature were varied according to strain requirements. Sugar utilization, ethanol production, attenuation, yeast viability, glycerol formation, ester concentration, sulfur compound development, pH reduction, and fermentation time were evaluated. The results show that ale yeast fermented more rapidly and produced higher ester levels, while lager yeast showed slower but cleaner fermentation with lower fruity aroma intensity. Specialty wort composition affected maltotriose uptake and residual extract differently between strains. The study demonstrates that yeast selection for specialty wort should consider sugar complexity, aroma target, attenuation requirement, and process duration together.