Preparation process of a composition enriched in phenolic compounds with a molecular weight of 400 Da or less from olive vegetation water, characterised in that it consists of: an optional acidification step of the vegetation water to achieve a pH of 4.3 or less; (a) a clarification step of said vegetation water by filtration, centrifugation or decantation; optionally, the three following steps to: the concentration of the acidified and clarified amurca for storage; the storage of concentrated acidified amurca; then the dilution in a solvent of the acidified amurca concentrated to approximately 4% of dry matter before performing step (b); (b) a tangential ultrafiltration step of the clarified vegetation water obtained in step (a) on a tubular ceramic membrane with a cut-off threshold ranging from 100 to 200 kDa and recovery of the permeate; (c) a nanofiltration step of said permeate obtained in step (b) on a spiral organic membrane with a cut-off threshold ranging from 150 to 400 Da at a pressure ranging from 1 to 3 MPa; said membrane is such that it comprises an active layer that comprises at least 50% polyamide and it enables to obtain a retentate comprising at least 80% of the dry matter contained in said vegetation water and a maximum of 25% of hydroxytyrosol; (d) an adsorption step of the phenolic compounds contained in the permeate obtained in step (c) by passage on a polymer matrix followed by elution of the phenolic compounds adsorbed onto said matrix with an organic polar solvent and obtainment of an eluate; (e) a concentration step by vacuum distillation of the eluate obtained in step (d), leading to a concentrate called composition A; and a drying step of said composition A. an optional acidification step of the vegetation water to achieve a pH of 4.3 or less; (a) a clarification step of said vegetation water by filtration, centrifugation or decantation; optionally, the three following steps to: the concentration of the acidified and clarified amurca for storage; the storage of concentrated acidified amurca; then the dilution in a solvent of the acidified amurca concentrated to approximately 4% of dry matter before performing step (b); (b) a tangential ultrafiltration step of the clarified vegetation water obtained in step (a) on a tubular ceramic membrane with a cut-off threshold ranging from 100 to 200 kDa and recovery of the permeate; (c) a nanofiltration step of said permeate obtained in step (b) on a spiral organic membrane with a cut-off threshold ranging from 150 to 400 Da at a pressure ranging from 1 to 3 MPa; said membrane is such that it comprises an active layer that comprises at least 50% polyamide and it enables to obtain a retentate comprising at least 80% of the dry matter contained in said vegetation water and a maximum of 25% of hydroxytyrosol; (d) an adsorption step of the phenolic compounds contained in the permeate obtained in step (c) by passage on a polymer matrix followed by elution of the phenolic compounds adsorbed onto said matrix with an organic polar solvent and obtainment of an eluate; (e) a concentration step by vacuum distillation of the eluate obtained in step (d), leading to a concentrate called composition A; and a drying step of said composition A. (a) a clarification step of said vegetation water by filtration, centrifugation or decantation; optionally, the three following steps to: the concentration of the acidified and clarified amurca for storage; the storage of concentrated acidified amurca; then the dilution in a solvent of the acidified amurca concentrated to approximately 4% of dry matter before performing step (b); the concentration of the acidified and clarified amurca for storage; the storage of concentrated acidified amurca; then the dilution in a solvent of the acidified amurca concentrated to approximately 4% of dry matter before performing step (b); (b) a tangential ultrafiltration step of the clarified vegetation water obtained in step (a) on a tubular ceramic membrane with a cut-off threshold ranging from 100 to 200 kDa and recovery of the permeate; (c) a nanofiltration step of said permeate obtained in step (b) on a spiral organic membrane with a cut-off threshold ranging from 150 to 400 Da at a pressure ranging from 1 to 3 MPa; said membrane is such that it comprises an active layer that comprises at least 50% polyamide and it enables to obtain a retentate comprising at least 80% of the dry matter contained in said vegetation water and a maximum of 25% of hydroxytyrosol; (d) an adsorption step of the phenolic compounds contained in the permeate obtained in step (c) by passage on a polymer matrix followed by elution of the phenolic compounds adsorbed onto said matrix with an organic polar solvent and obtainment of an eluate; (e) a concentration step by vacuum distillation of the eluate obtained in step (d), leading to a concentrate called composition A; and a drying step of said composition A.