A process of extracting or purifying proteinaceous material and/or fibraceous material from brewer's spent grain (BSG), the process comprising the steps of: Providing brewer's spent grain； Performing saccharification by enzymatic treatment of the brewer's spent grain and a fermentation of the saccharified brewer's spent grain with lactic acid bacteria and/or acetic acid bacteria and/or probiotics to obtain a fermented broth； and extracting and/or purifying proteinaceous and/or fibraceous material from the fermented BSG.
