The departure of the Jovian magnetosphere from rigid corotation is adequately explained by outward plasma transport at distances L>10. The departure of 5% observed in the Io plamsa torus, however, is too large to be accounted for simply by plasma transport. We propose local plasma production to be the main factor determining the corotation lag in the torus. We calculate the outward pick-up current provided by ionization of neutral atoms and relate this to the current produced in the ionosphere by the corotation lag. This leads to an expression giving the corotation lag of the torus as a function of radial distance. Charge transfer is found to be several times that inferred from examination of the corotation lag associated with outward plasma transport.