An apparatus to deliver gas into a liquid comprising a container for the gas to be injected, which is connected to a compressed gas source (1) by means of an inlet duct, said gas delivering apparatus comprising at least one sensor to measure pressure and one sensor to measure temperature, wherein said container is a measurement chamber (9) of known volume, which is connected to a final delivery system or injector (10) by means of an outlet duct, wherein the final delivery system or injector comprises a long application tube with a diffuser that allows the gas to be divided into very small bubbles to facilitate its dissolution into the liquid. A method to deliver a gas into a liquid comprising a) allowing the passage of a determined amount of gas into a container for the gas to be injected, wherein said method comprises the steps of: b) measuring the pressure difference and the gas temperature inside the gas container, being said container a measurement chamber with a constant volume; c) allowing the discharge of a gas dose in a predetermined amount of gas, measured in step b), by activating the application system; d) injecting the gas into the bulk of the liquid. The method of the present invention finds application mainly in the wine industry, wherein sulfur dioxide application is required to control fermentation.