Spent grain is the most abundant waste product, accounting for around 85% of total waste, and is therefore the largest issue for waste management in the brewing industry (Mussatto, 2014). The spent grain originates from barley, hops, and other cereal malts which are used as a source of flavour and sugar for fermentation. The brewery spent grain (BSG) is more than 75% moisture and still contains high levels of nutrients. The high moisture content creates issues with inefficient off-site transportation due to its weight, thus increasing the costs of waste management. The high levels of nutrients in the spent grain create a breeding ground for potential contaminants, allowing rapid colonisation for fungi and bacteria. The BSG also encourages pests and rodents, which harbour undesirable micro-organisms, leading to the potential contamination of the beer (Thomas & Rahman, 2006).

 

 

There is an urgent need to remove the spent grain off-site to ensure the quality of the beer produced. Due to the established connection between the beer industry and the agricultural industry, most of this spent grain is used as fertiliser, compost and feed. The carbon to nitrogen (C:N) ratio, ranging from 17:1 to 12:1, shows that the spent grain is a good source of nitrogen for compost piles. Although the high levels of moisture are good for composting, the value of the BSG can be vastly increased by drying the grain and reducing moisture to less than 3%. This not only reduces transportation costs, but concentrates the nutrients in the grain, making the dried grain a more effective fertiliser. Unfortunately, due to the high costs involved in drying the BSG, this method of waste management is uneconomical for most small scale breweries (Seefeldt, 2015).

 

 

Investigations into different methods of disposal and other uses for BSG are being conducted worldwide. Some potential applications of the spent grain are protein concentrates, support for cell immobilisation, cultivation of micro-organisms for single cell protein productions and oil extraction. The major developments in recycling the BSG are in the food industry, focussing on further production of the grain for human nutrition or re-fermenting the grain to obtain a low-alcohol beer. As the spent grain still contains one fifth of its original nutrients (Santos Mathias, Moretzsohn de Mello & Servulo, 2014), there is plenty of scope for expansion and development for the use of the spent grain.