The process for the production of alcohol and/or solvent from a biomass feedstock comprises the stages for pretreatment (P) of the biomass feedstock, for enzymatic hydrolysis (H1 and HF), and for fermenting the hydrolyzate (HF). To prevent solids from being sent and to facilitate operating the section for purifying the fermentation products, at least a portion of the solid material in the fermentation wine is extracted (Ex1) to obtain a stream of solid residue (11) comprising lignin and a fermentation wine (12) that is low in solid material. Then, the stream of solid residue is washed (L) with a liquid stream to recover a liquid stream that is enriched with fermentation products (16). The liquid stream that is enriched with fermentation products (16) is recycled in the enzymatic hydrolysis stage (H1) to recover any fermentation product and to increase the overall yield of the process.