A device for protecting a liquid from oxidation inside a container includes a first element supplying the liquid inside the container, a second element supplying the liquid outside the container and a control unit. A pneumatic control system is configured to produce an overpressure inside the container and on the liquid when the liquid is supplied outside the container, such that, following a decrease in the volume of the liquid inside the container, the pneumatic control system increases its volume by an amount equal to the change in the volume of the liquid. The pneumatic control system includes a variable capacity tank and a pipe supplying and discharging a fluid for filling the tank. A system supplying and discharging the filling fluid is connected to the pipe and the supplying and discharging pipe communicates with the variable capacity tank through a connection placed inside the container at its lower end.