The present invention relates to a process for reacting epoxides with an initiator compound in the presence of a double metal cyanide compound as a catalyst, said process having a shortened induction period, and the double metal cyanide compound being activated by adding the epoxide to a mixture of double metal cyanide compound and initiator compound at an internal reactor pressure of less than 1 bar, and also to the polyethers themselves obtainable by such a process.