Bilateral teleoperation under rate mode is known to be a difficult problem in terms of stability, especially when the slave manipulator interacts with a time-varying environment. This paper presents an energy based variable admittance control approach, whose principle combines the monitoring and the regulation of the energy exchanges with a passivity tank. It allows stable interactions with force feedback for any desired inertia, damping and stiffness parameters. Experiments are conducted to assess the efficiency of the proposed approach using an experimental setup with a variable stiffness environment. The obtained results illustrate the ability of the proposed strategy to stabilize a system otherwise unstable, with little effect on the transparency of the teleoperation system.