Abstract
Brewer’s spent grain is the largest solid by-product in brewing and contains residual fibres, proteins, phenolic compounds, and fermentable substrates that can support sustainable recovery pathways. This study examines spent grain valorization and fermentation by-product recovery in sustainable brewing. Spent grain samples were collected after mashing and processed through drying, extraction, enzymatic hydrolysis, and controlled secondary fermentation. Fibre recovery, protein solubilization, phenolic extraction, residual sugar release, organic acid production, ethanol potential, and waste reduction efficiency were evaluated. The results show that enzymatic hydrolysis improved sugar availability and increased recovery of fermentable compounds from spent grain. Secondary fermentation generated useful organic acids and low-level ethanol fractions, while solid residues retained value for feed or fibre applications. Excessive thermal drying reduced phenolic recovery and increased processing energy demand. The study demonstrates that spent grain can be converted into value-added fermentation streams when recovery conditions are optimized for both yield and sustainability.