NOVELTY - Recovering protein-containing fermentation agent, comprises: (i) forming aqueous mixture of organic material and protein-containing fermentation agent; (ii) fermenting aqueous mixture to produce ethanol; (iii) recovering ethanol stream of ethanol and co-product stream; (iv) subjecting co-product stream to first separation stage to recover first stream of unfermented organic material and second stream of fermentation agent suspended in aqueous solution; and (v) subjecting second stream to second separation to recover third stream of fermentation agent and fourth stream of aqueous solution.    USE - The processes are useful in: recovering protein-containing fermentation agent; treating stillage; and producing animal feed composition, protein-containing composition, ethanol and protein-containing fermentation agent, where the protein-containing composition and animal feed composition are useful for stimulating growth in an animal (e.g. cattle, sheep, goats, pigs, poultry, fish, crustacea, horses, cats and dogs) (all claimed).    ADVANTAGE - The process of recovering protein-containing fermentation agent: recovers the yeast with high quantity in a cost effective manner; and recycles the recovered undissolved unfermented organic material to improve the yield of fermentation agent.    DETAILED DESCRIPTION - Recovering a protein-containing fermentation agent, comprises: (i) forming an aqueous mixture of an organic material and a protein-containing fermentation agent capable of fermenting the organic material to produce ethanol; (ii) fermenting the aqueous mixture to produce ethanol; (iii) recovering from the fermented aqueous mixture an ethanol stream which is rich in ethanol and a co-product stream comprising unfermented organic material, fermentation agent and an aqueous solution of dissolved solids in water; (iv) subjecting the co-product stream to a first separation stage to recover a first stream rich in the unfermented organic material and a second stream rich in the fermentation agent suspended in the aqueous solution; and (v) subjecting the second stream to a second separation step, capable of recovering suspended solids from a liquid, to recover a third stream rich in the fermentation agent and a fourth stream rich in the aqueous solution. INDEPENDENT CLAIMS are also included for:    (1) preparing an animal feed composition, comprising recovering the fermentation agent, and combining the fermentation agent with a carbohydrate source, optionally an additional protein source and optional additives, where the fermentation agent comprises at least 2 wt.% of the animal feed composition;    (2) treating stillage (obtained from a fermentation process and comprises water, yeast, suspended fibrous and non-fibrous solids and dissolved solids) comprising: separating the majority of the suspending fibrous solids from the rest of the stillage; and then separating the majority of the yeast from the water and dissolved solids;    (3) an animal feed composition prepared by the process of recovering protein-containing fermentation agent, where the animal feed composition comprises a protein-containing composition (2-40 wt.%);    (4) apparatus for producing ethanol and a protein-containing fermentation agent comprising: a fermentation stage for fermenting an aqueous mixture comprising an organic material and a fermentation agent capable of fermenting the organic material, to produce ethanol; a first separation stage for recovering the ethanol from the unfermented aqueous mixture; a second separation stage, downstream of the first separation stage for recovering unfermented organic material from the fermentation agent and from an aqueous solution of dissolved solids in water; and a third separation stage, downstream of the second separation stage, for recovering the fermentation agent from the aqueous solution; and    (5) a protein-containing composition obtainable by the process of recovering protein-containing fermentation agent, where the protein-containing composition comprises yeast in combination with at least one non-starch polysaccharide (NSP), and the yeast comprises at least 60 wt.% of the composition, based on the dry weight of the composition.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic drawing of the process for recovering fermentation agent, in particular yeast.    Pressing solids output into a cake (36)    Drying the cake (42)    Pelletizing the cake (44)    Producing water in a stream (48)    Producing the yeast in a stream (52)