Abstract
Fermentation by-products such as higher alcohols, sulfur compounds, aldehydes, and vicinal diketones can reduce beer quality when yeast nutrition is poorly controlled. This study investigates reduction of fermentation by-products through controlled yeast nutrition. Brewing fermentations were conducted with varied assimilable nitrogen, vitamins, minerals, and oxygen availability while maintaining constant wort gravity, yeast strain, pitching rate, and temperature. Yeast growth, attenuation, ethanol yield, amino nitrogen uptake, diacetyl concentration, acetaldehyde formation, hydrogen sulfide release, higher alcohol production, and sensory quality were evaluated. The results show that insufficient nitrogen increased sluggish fermentation and sulfur-related off-flavours, while excessive nutrient supplementation promoted higher alcohol formation. Balanced yeast nutrition supported complete attenuation, faster diacetyl reduction, lower acetaldehyde concentration, and cleaner flavour expression. The study demonstrates that by-product reduction depends on matching nutrient availability with yeast metabolic demand. Controlled yeast nutrition provides a practical route for improving fermentation consistency and final beer quality.