A method of producing a composition comprising one or more galacto-oligosaccharide(s), the method comprising the steps of: a) providing a mixture comprising - a galactosyl donor comprising a galactosyl group bound to a leaving group, which galactosyl donor has a molar weight of at most 350 g/mol, - a galactosyl acceptor which is different from the galactosyl donor, said galactosyl acceptor is a saccharide or a sugar-alcohol, and wherein the molar ratio between the galactosyl acceptor and the galactosyl donor is at least 1:10, and wherein the mixture comprises at least 0.05 mol/L of the galactosyl acceptor, b) providing a first enzyme, said first enzyme having beta-galactosidase activity and transgalactosylating activity, said first enzyme contacting the mixture, and c) incubating the mixture and the first enzyme, thereby allowing the first enzyme to release the leaving group of the galactosyl donor and transfer the galactosyl group of the galactosyl donor to the galactosyl acceptor, thus forming the galacto-oligosaccharide, step c) furthermore comprising removing from the incubating mixture a leaving group released from the galactosyl donor and wherein the removal of the leaving group released from the galactosyl donor involves physical removal of free leaving groups from the incubating mixture and/or conversion of free leaving groups into one or more other chemical species which may still be present in the incubating mixture, thereby obtaining the composition comprising the one or more galacto-oligosaccharide(s). a) providing a mixture comprising - a galactosyl donor comprising a galactosyl group bound to a leaving group, which galactosyl donor has a molar weight of at most 350 g/mol, - a galactosyl acceptor which is different from the galactosyl donor, said galactosyl acceptor is a saccharide or a sugar-alcohol, and wherein the molar ratio between the galactosyl acceptor and the galactosyl donor is at least 1:10, and wherein the mixture comprises at least 0.05 mol/L of the galactosyl acceptor, - a galactosyl donor comprising a galactosyl group bound to a leaving group, which galactosyl donor has a molar weight of at most 350 g/mol, - a galactosyl acceptor which is different from the galactosyl donor, said galactosyl acceptor is a saccharide or a sugar-alcohol, and b) providing a first enzyme, said first enzyme having beta-galactosidase activity and transgalactosylating activity, said first enzyme contacting the mixture, and c) incubating the mixture and the first enzyme, thereby allowing the first enzyme to release the leaving group of the galactosyl donor and transfer the galactosyl group of the galactosyl donor to the galactosyl acceptor, thus forming the galacto-oligosaccharide, step c) furthermore comprising removing from the incubating mixture a leaving group released from the galactosyl donor and wherein the removal of the leaving group released from the galactosyl donor involves physical removal of free leaving groups from the incubating mixture and/or conversion of free leaving groups into one or more other chemical species which may still be present in the incubating mixture, thereby obtaining the composition comprising the one or more galacto-oligosaccharide(s).