BACKGROUND Brewers spent grains (BSG) represents ≤85% of a brewery's solid waste and common disposal to landfill is increasingly more difficult. Yet BSG is a food‐grade by‐product with potential economic valorization that can significantly improve resource efficiency and reduction in carbon emissions. This study investigated valorization of BSG through the application of novel high solids hydrothermal processing technology in a small‐scale biorefinery, annexed to a brewery. It focused on three scenarios for the production of: (A) the sugar replacement xylitol; (B) prebiotic xylo‐oligosaccharide (XOS); and (C) co‐production of xylitol and XOS. Economic assessment was conducted by comparing the capital and operating expenditure from process simulations created in Aspen Plus®. The process models developed were supplemented with experimental data to improve accuracy. RESULTS Internal rate of return (IRR) values obtained were greater than the hurdle rate of 9.7% for all scenarios when considering a conservative market price for xylitol and XOS as US$4500 t–1, yet dedicated production of XOS was economically more favourable with a minimum required selling price (MRSP) of US$2509 t–1 compared to US$4153 t–1 for xylitol. Additionally, the scenario for co‐production of xylitol and XOS achieved the lowest MRSP of US$2182 t–1. By‐products significantly contributed to 32.7%, 14.2% and 27.5% of the revenue generated in scenarios A, B and C, respectively. CONCLUSION These results provide a good platform from which to develop the cost‐effective commercial production of XOS and xylitol from BSG. © 2021 Society of Chemical Industry

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Brewers' spent grains (BSG) make up to 85% of a brewery's solid waste, and is either sent to land ll or sold as cheap animal feed supplement. Xylo-oligosaccharides (XOS) obtained from BSG are antioxidants and prebiotics that can be used in food formulations as low-calorie sweeteners and texturisers. The effect of extremely low acid (ELA) catalysis in liquid hot water (LHW) hydrothermal treatment (HTT) was assessed using BSG with dry matter contents of 15% and 25%, achieved by dewatering using a screw press. Batch experiments at low acid loadings of 5, 12.5 and 20 mg/g dry mass and temperatures of 120, 150 and 170 °C signi cantly affected XOS yield at both levels of dry mass considered. Maximum XOS yields of 76.4% (16.6 g/l) and 65.5% (31.7 g/l) were achieved from raw BSG and screw pressed BSG respectively, both at 170 °C and using 5 mg acid/g dry mass, after 15 min and 5 min, respectively. These XOS yields were obtained with BSG containing up to 63% less water and temperatures more than 20 °C lower than that reported previously. The nding con rms that ELA dosing in LHW HTT allows lowering of the required temperature that can result in a reduction of degradation products, which is especially relevant under high solids conditions. This substantial XOS production intensi cation through higher solids loadings in HTT, not only achieved high product yield, but also provided bene ts such as increased product concentrations and decreased process heat requirements.

Brewers’ spent grains (BSG) make up to 85% of a brewery’s solid waste, and is either sent to landfill or sold as cheap animal feed supplement. Xylo-oligosaccharides (XOS) obtained from BSG are antioxidants and prebiotics that can be used in food formulations as low-calorie sweeteners and texturisers. The effect of extremely low acid (ELA) catalysis in liquid hot water (LHW) hydrothermal treatment (HTT) was assessed using BSG with dry matter contents of 15% and 25%, achieved by dewatering using a screw press. Batch experiments at low acid loadings of 5, 12.5 and 20 mg/g dry mass and temperatures of 120, 150 and 170 °C significantly affected XOS yield at both levels of dry mass considered. Maximum XOS yields of 76.4% (16.6 g/l) and 65.5% (31.7 g/l) were achieved from raw BSG and screw pressed BSG respectively, both at 170 °C and using 5 mg acid/g dry mass, after 15 min and 5 min, respectively. These XOS yields were obtained with BSG containing up to 63% less water and temperatures more than 20 °C lower than that reported previously. The finding confirms that ELA dosing in LHW HTT allows lowering of the required temperature that can result in a reduction of degradation products, which is especially relevant under high solids conditions. This substantial XOS production intensification through higher solids loadings in HTT, not only achieved high product yield, but also provided benefits such as increased product concentrations and decreased process heat requirements.