Brewers' spent grain (BSG), the main by-product of the beer industry, represents a sustainable source of protein and fiber. This study developed and characterized hybrid stirred yogurts by partially replacing whole milk powder with BSG while maintaining a fixed total protein content (3.75% w/w). Four formulations (0, 2.5, 5.0, and 7.5% BSG) were produced, and their fermentation kinetics, physicochemical, microbiological, rheological, textural, and sensory properties were evaluated over 28 days at 5 ◦C. Partial substitution with BSG affected the fermentation rate, reduced pH, and modulated starter culture growth, while increasing dietary fiber. BSG also disrupted the protein network, producing higher syneresis, and decreased viscosity, firmness, and consistency, with stronger effects at ≥ 5.0% BSG. Sensory evaluation revealed that only the 2.5% formulation aligned with the control yogurt, as higher BSG levels noticeable changed mouthfeel and visual attributes. Low BSG inclusion may balance nutritional improvement and consumer acceptability.