Process for producing a hydrophobic composite bioelastomer, comprising a cross-linked bioelastomer matrix in which an organic phase is dispersed, comprising the reaction of cross-linking of a hydroxyl-terminated polysiloxane with a silane coupling agent, comprising an acetoxysilane, to obtain a cross-linked polysiloxane with release of acetic acid. The reaction of cross-linking is carried out in the presence of starch to cause at least partial in situ acetylation by the acetic acid released from said starch that is incorporated in the cross-linked bioelastomer matrix.