During the brewing process, yeast is added to initiate fermentation, converting sugar to alcohol and carbon dioxide (CO2). Before full maturation of the beer, the excess yeast is collected and can be re-used in the brewing process up to around six times. After this, it becomes brewer’s spent yeast (BSY) – the second biggest by-product of the brewing process (15% of total by-products generated).
BSY contains a high level of nutrients and there are several technologies that can turn this waste into a valuable resource. However, BSY is highly susceptible to rapid contamination and spoilage as a result of the activity of microorganisms. This has hampered the large-scale use of some technologies for reusing BSY. Drying the spent yeast can make it last longer, but this is an expensive process that requires large amounts of energy.
Currently outside of Europe, the brewer AB InBev has extensive drying operations to produce dried brewer’s yeast, which can be sold for use in human food and animal nutrition (mostly pet food). However, most of the BSY produced by the company in Europe (some 125 000 tonnes/yr) is sold in its wet form as inexpensive animal feed to farmers – only 10% is processed in drying installations due to the costs involved.