Disclosed is a method for producing alpha-calcium sulfate hemihydrate from calcium dihydrate. Said method has the following features: a) calcium dihydrate is fed to an agitated autoclave (1); b) the agitated autoclave (1) is indirectly heated; c) water is added and incorporated in a controlled manner; d) the feedstock is prevented from adhering to surfaces of the reaction chamber by means of moved chains (3) that are mounted on the paddles and/or the drive shaft (16) of the agitated autoclave (1); e) the pressure in the reaction chamber is regulated at intervals or in a continuous manner by discharging vapor when a certain pressure has been reached in the interior, the vapor being conducted via a centrifugal separator (17) and a control valve (18); f) cold air is delivered for residual drying purposes; g) the process material is removed. Also disclosed is a corresponding apparatus for carrying out said method.