Brewer's spent grain (BSG) is the most abundant side-stream from the brewing industry. The annual production of BSG is ca. 30 million tons, worldwide. BSG contains valuable nutrients such as protein but is at the moment underutilized. The protein component in BSG has potential to be used as a source of human and animal dietary protein, if it can be extracted without too much deterioration. In this study BSG protein solubility was studied in differing conditions.