NOVELTY - Producing (m1) fermentation product involves providing a feedstock slurry comprising fermentable carbon source, undissolved solids and oil; separating a portion of the undissolved solids and oil from the feedstock slurry where an aqueous solution comprising fermentable carbon source, a wet cake comprising solids and an oil stream are formed; and adding the aqueous solution to a fermentation broth comprising microorganisms where the fermentation product is produced.    USE - For producing fermentation product such as ethanol, propanol, butanol, pentanol, hexanol and fusel alcohol (claimed).    ADVANTAGE - The process separates feed stream components prior to the fermentation and controls the amount of undissolved solids and/or oil in the fermentation process; and provides a mechanism to develop co-product compositions for the needs of different markets, such as animal feed markets requiring higher protein or higher fat feeds. An increase in phase separation between fermentation broth and extractant reduces the likelihood of emulsion formation resulting in an increased efficiency of product alcohol production. The presence of oil in the fermentation process has an effect on the partition coefficient of the extractant over the course of multiple fermentations. Removing oil from the feedstock or feedstock slurry reduces the variability of the partition coefficient of the extractant over the course of multiple fermentations, and therefore improves the scalability of the processes and systems.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) method (m2) involving providing a feedstock slurry comprising fermentable carbon source and undissolved solids; separating at least a portion of the undissolved solids from the feedstock slurry where an aqueous solution comprising fermentable carbon source and a wet cake comprising solids are generated; contacting the wet cake with a liquid to form a wet cake mixture; and separating at least a portion of undissolved solids from the wet cake mixture where a second aqueous solution comprising fermentable carbon source and a second wet cake comprising solids are generated;    (2) method (m3) involving providing a feedstock slurry comprising fermentable carbon source, undissolved solids, and oil; separating at least a portion of the oil and undissolved solids from the feedstock slurry where an aqueous solution comprising fermentable carbon source, oil stream and wet cake comprising solids are generated; contacting the wet cake with a liquid to form a wet cake mixture; and separating at least a portion of undissolved solids and oil from the wet cake mixture where a second aqueous solution comprising fermentable carbon source, a second oil stream; and a second wet cake comprising solids are generated;    (3) method (m4) involving providing a feedstock slurry comprising fermentable carbon source, undissolved solids, and oil; separating the feedstock slurry where (i) a first aqueous solution comprising a fermentable carbon source, (ii) a first wet cake comprising solids, and (iii) a stream comprising oil, solids, and an aqueous stream comprising a fermentable carbon source are formed; and adding the first aqueous solution to a fermentation broth comprising microorganisms where a fermentation product is produced;    (4) method (m5) involving providing a feedstock slurry comprising a fermentable carbon source, undissolved solids and oil; separating the feedstock slurry where (i) a first aqueous solution comprising a fermentable carbon source and solids, (ii) a first wet cake comprising solids, and (iii) a first oil stream are formed; and adding oil to the first aqueous solution where an oil layer comprising solids and a second aqueous solution comprising a fermentable carbon source are formed;    (5) system comprising liquefaction units configured to liquefy a feedstock to create a feedstock slurry, the liquefaction unit comprising an inlet for receiving the feedstock; and outlet for discharging a feedstock slurry, where the feedstock slurry comprises fermentable carbon source, oil and undissolved solids; and separation units configured to remove the oil and undissolved solids from the feedstock slurry to create an aqueous solution comprising the fermentable carbon source, an oil stream and wet cake comprising the portion of the undissolved solids, the centrifuge comprising an inlet for receiving the feedstock slurry; first outlet for discharging the aqueous solution; second outlet for discharging the wet cake; and third outlet for discharging the oil.