Global beer production generates over 38 million tonnes of waste annually, primarily as brewer’s spent grain and barley malt rootlets, which are typically used as low-value animal feed or discarded to landfill. These waste products contain hordatines, a unique class of phenolamides expressed in barley that are thought to contribute to the astringent flavour of beer and exert antifungal activity. Formed via the dimerization of hydroxycinnamoyl agmatines, hordatines are categorised into four main structural types (A, B, C, D) that can be further modified via hydroxylation, methylation and glycosylation. However, the full extent of hordatine structural variation has not been explored. In this work, liquid chromatography coupled to drift time ion mobility mass spectrometry is used to study hordatines isolated from beer waste products for the first time. 169 unique hordatine structures could be identified in a single sample by accurate mass, with extensive isomerism captured by the added dimension of ion mobility. Clear structural trends among these compounds were apparent, with these tentatively assigned to previously characterised stereoisomers resulting from the hydroxycinnamoyl agmatine dimerization process, with in silico collisional cross section calculations supporting this. This work demonstrates the immense structural heterogeneity of hordatines in beer waste products and gives insight into the underlying chemistry that controls their biosynthesis. Understanding the chemical composition of beer waste products will enable their transformation into value-adding commodities in the food and health industries, reducing global waste and leading us closer to a circular economy.