Food Applications, Composition, and Sustainability Trade-Offs of Bourbon Distillers' Spent Grain: A Critical Review.

Bourbon distillers' spent grain (DSG-B) is a protein- and fiber-rich coproduct generated during bourbon production that has emerging potential as an upcycled food ingredient. Unlike conventional corn distillers' dried grains with solubles and brewer's spent grain, DSG-B arises from bourbon-specific processing conditions, including multigrain mash bills, on-grain fermentation, and variable post-distillation handling, all of which may influence its composition, functionality, and consistency. This critical review evaluates the current state of knowledge on DSG-B with emphasis on composition, functional properties, safety considerations, food applications, and selected sustainability implications relevant to food use. Available bourbon-specific studies indicate that DSG-B contains approximately 25%-34% crude protein and 29%-70% total dietary fiber on a dry basis, with insoluble fiber predominating and lysine availability likely limited by the corn-based protein matrix and thermal processing history. Among reported food applications, extrusion has the strongest bourbon-specific evidence, with particle size and inclusion level shown to significantly affect expansion, porosity, hardness, and fiber enrichment; formulations containing up to 10% DSG-B at about 300 µm have demonstrated acceptable product quality. In contrast, bakery applications remain less developed and are supported largely by older or non-bourbon-specific literature. Major gaps persist in food safety data, contaminant surveillance, sensory validation, phenolic characterization, and protein-quality assessment using methods such as the Digestible Indispensable Amino Acid Score or reactive lysine analysis. Overall, DSG-B represents a promising value-added ingredient, but broader food applications will require compositional standardization, targeted functionality studies, safety validation, and product-specific optimization.