Improving Brewery Sustainability: Upcycling the Discarded Byproducts Trub, Spent Hops, and Yeast as Livestock Feed Additives

Craft breweries generate a complex set of byproducts that exceed 2 million tons annually. Their disposal possesses material handling, financial, and environmental challenges. A mixture of these, namely trub, hops, and yeast, designated THYM ® , was evaluated biochemically and in a feeding trial to enhance its valuation. THYM contained approximately 3% α plus β hop acids, 0.2% xanthohumol (XN), and 35% crude protein. It exhibited antimicrobial activity, with a minimum inhibitory concentration of 137 ± 39 μg/mL for B. subtilis , and antioxidant activity, with 90 ± 13 μmol/g of Trolox equivalents. THYM presented positive results in bovine rumen microbial in vitro fermentations, decreasing methane production and the acetate:propionate ratio at 3 mg/mL. These results led to a nine-week feedlot trial with 45 Black Angus weanling steers on either a corn silage-based diet (CON), CON with monensin (MON) at 200 mg/animal, or CON with 1% THYM (THYM). Data were analyzed by SAS 9.4 with two orthogonal contrasts of CON vs. MON and THYM and MON vs. THYM. While average daily gain (ADG) and dry matter intake (DMI) did not differ among treatments, a tendency was observed for the THYM and MON groups to have a greater gain to feed ratio (ADG:DMI) when compared to CON ( p = 0.07). The XN metabolite 8-prenylnarigenin, a potent phytoestrogen, was present in the serum of the THYM group at 4.0 ± 0.9 nM by mass spectrometry. These brewing byproducts, which can be drum-dried, were well tolerated and show potential value as a cattle growth promoter.