A method of processing spent grains by removing suspended solids from the spent grains to produce a stream low in suspended solids, directing the stream low in suspended solids to an anaerobic digester, converting at least some soluble compounds to biogas, and producing a biogas. A method of processing spent grain, by separating a first stream consisting of spent grains into a second stream and a third stream wherein the second stream contains a majority of suspended solids, separating the third stream into a fourth stream and a fifth stream wherein the fifth stream is lower in suspended solids than the fourth stream, directing the fifth stream to an anaerobic digester, and converting at least some organic compounds to a biogas. A method of fermenting a grain product.
