UC Davis

In 2020, global beer production reached a staggering volume of 1.82 trillion hectoliters, resulting in the generation of 36.4 million metric tons of brewers spent grain (BSG) (Zeko-Pivač et al. 2022). BSG primarily consists of the husk, pericarp, and seed coats of barley, making it a highly fibrous material. Trace amounts of silica, polyphenols, insoluble protein, and oils may also be present (Mussatto et al. 2006). The water content of BSG ranges from 60-90%; which allows naturally present microbes spoil the material within a few months of cold, sealed storage and within days of room temperature sealed or open air storage (Briggs et al. 2004; Mallen & Najdanovic-Visak 2018). The water content also contributes to the weight of BSG, increasing transportation costs and resource demand for disposing grain offsite. Traditionally, brewers donate their BSG to farmers as animal feed, however there is growing interest in alternative opportunities to valorize the grain. This research first provides an overview of the current BSG-derived products on the market, including dog treats, compound extraction, industrial materials, and beyond. Subsequently, it evaluates a biorefinery model which converts BSG into biochar using waste caustic material from the brewing process, specifically considering optimization of each step in the protocol to produce a biochar product. The ideal production parameters were found to be 1 day of soaking BSG in caustic at a dosage rate of ≤ 5 moles per 100 g unprocessed BSG at ambient temperature, followed by draining of the liquid fraction, drying of the BSG until constant weight, grinding until uniform particle size, and pyrolysis at 700 °C with a heating rate of 5 °C/min, holding the sample for at least 1 hour of residence time with constant inert gas flow throughout the heating and cooling process. The resulting biochar was appropriate for water filtration or soil amendment systems within the brewing industry (assuming further processing), which would allow brewers to build circular economy model. The proposed method was then evaluated via a greenhouse gas (GHG) assessment, to determine the efficacy of implementing this system in industry. The findings of this study concluded that landfilling BSG released nearly 3 kg CO2e per kg unprocessed BSG, while processing BSG into biochar at the lab scale resulted in lower emissions of 1.175 kg CO2e per kg unprocessed BSG. Based on these results, it is strongly recommended that BSG is diverted from landfills and utilized in more environmentally sustainable ways, such as through biochar production, composting, or a relative biorefinery process. By adopting a circular economy model for BSG, breweries can contribute to resource efficiency, waste reduction and the creation of sustainable value chains.