Bone graft substitute compositions and methods of making the compositions are disclosed. In some embodiments, a method of making a composition includes contacting a mixing solution with a first mixture having calcium sulfate hemihydrate and a plasticizing material to form a second mixture; waiting a predetermined period of time after forming said second mixture; and then contacting demineralized bone with the second mixture to form the composition. A composition can be formed from a kit including a first mixture having calcium sulfate hemihydrate and a plasticizing substance, a second mixture having demineralized bone, and a mixing solution. The first and second mixtures and the mixing solution are unblended.