# Potential Applications of Yeast Biomass Derived from Small-Scale Breweries
## 2 Brewery Industry Waste and By-Products  
Over the past three decades, extensive research and practical implementations have introduced numerous technologies to the brewing industry, affording notable efficiencies in production, notably those that curtail the generation of by-products. Nevertheless, certain waste streams inherently associated with beer production are difficult to reduce. New strategies in brewery waste management should not only facilitate disposal but also aim to extract additional value from processing whenever feasible. Residual materials, including  
Figure 1: World beer production share in 2022 [1]. spent grain, hot truly generated in the brewing process, and brewer's yeast, present disposal challenges owing to their complex physicochemical properties and microbiological activity. The disposal process itself is characterized by considerable costs [6]. According to data from the European Environment Agency in 2022, the average cost of waste disposal in Poland was EUR 60 per ton [7]. However, as indicated by the \"Committed to the Environment\" report, this value could increase by an additional EUR 533 per ton of waste by 2030 [8]. Taking into account only the spent grain (20 kg/hL) and yeast (3 kg/hL) in the calculations, the additional cost of waste disposal could reach up to EUR 13.64 per hectoliter of beer. These aforementioned waste components also contribute to a loss of up to 20 L of water per every 100 L utilized in the production process, and this is particularly pronounced in instances involving hot truly and brewer's yeast, where the water content can constitute up to 90% of the overall volume [9]. The disposal of brewing waste generates numerous ecological challenges due to its substantial nutritional value and elevated concentrations of organic compounds, thereby imposing a significant chemical and 5-day biochemical oxygen demand (COD and BOD5) during degradation [10]. Given various factors that encompass environmental policy, the advocacy for the \"zero waste\" philosophy, the presently observed scarcity of non-renewable resources, and challenges associated with the inappropriate utilization of renewable resources collectively necessitate the development of innovative technologies aimed at minimizing waste generation or facilitating the reutilization of produced waste in order to enhance the overall value added. The largest beer companies, representing approximately 95% of the global beer production worldwide, possess an extensive infrastructure tailored for the efficient treatment of production-derived wastewater. In addition, these establishments yield substantial volumes of valuable by-products; thanks to their abundant supply, economic viability is realized through various processing methods, such as the incorporation of by-products into animal feed production. Conversely, the minority share of the market is served by small craft breweries, whose production outputs of most by-products are insufficient for economically viable utilization. Consequently, these smaller enterprises confront the challenge of disposing of by-products effectively, which, nonetheless, constitute valuable substrates for diverse sectors of the industrial landscape. While the issue of spent grain presents a relatively minor challenge, with a supply ranging from 14 to 20 kg/hL deemed sufficient for small-scale farmers or modest processing facilities, more formidable difficulties arise in the context of yeast slurry [9]. The latter constitutes a significant environmental burden, and the prevailing methods of its disposal are economically infeasible in the face of limited supply levels. Post-production yeast slurry is not added to brewing wastewater, because the wastewater is already heavily polluted with contaminants from different production stages, including cleaning. Yeast slurries are characterized by a high content of organic matter (BOD5: 76,000 mg/g of DW; 1250-1350 mg of COD/g of DW; COD calculation details in Table S3), nitrogen (up to 7.5% of DW), and phosphorus (around 1% of DW) [11; 12].