Brewer’s spent grain particle size and substitution level influence physicochemical and sensory properties of enriched cookies

Abstract Brewer’s spent grain (BSG) is a rich nutrient by-product generated during beer production; however, its industrial application in food products remains limited. This research investigated the effect of BSG particle sizes ( d 4,3 = 756.67, 561.67, and 158.33 μm) and substitution levels (10%, 20%, and 30%) on the physicochemical and sensory characteristics of cookies, while the nutritional composition was evaluated for cookies containing medium-sized BSG. Unlike conventional preparation methods, the BSG powder used in this study was milled under controlled conditions without sieving to ensure consistent composition across particle sizes and allow the direct evaluation of particle size effects. Results indicated that BSG had superior water and oil retention capacities compared to wheat flour, with larger particles exhibiting higher absorption. Enrichment with BSG significantly improved the protein, dietary fiber, ash, and phenolic content, along with antioxidant capacity, all of which increased with the substitution percentage. Textural analysis showed a reduction in cookie hardness and spread ratio upon BSG addition, particularly with larger particle sizes and higher inclusion levels. Color analysis revealed darker cookie shades as BSG content increased and particle size decreased. Sensory testing suggested that acceptable substitution levels rose from 20% for coarse BSG to 30% for medium and fine forms. Overall, cookies containing medium-sized BSG at 30% substitution achieved the most balanced profile in terms of nutrition, texture, and consumer acceptance.