Brewer's spent-grain based protein powder and related methods for using producing protein-enhanced foodstuff. The brewer's spent-grain based protein powders have beneficial properties including low phytic acid content, high PDCAAS value and retention of significant antioxidant properties. The brewer's spent-grain based protein powders are highly soluble and thus are easily wetable, readily dispersable and blendable in concentrations of up to 50% by weight. The brewer's spent-grain based protein powder possesses beneficial sensory characteristics including light color and mild flavor that allow the brewer's spent-grain based protein powder to be used alone or as a protein value enhancer within foods intended for human consumption, companion pet foods and in commercial livestock feeds.