An apparatus and method are provided for mixing a gas and a liquid to produce a gaseous vapor of the liquid that is substantially free of droplets. Gas, e.g., carbon dioxide, is divided into first and second streams. The first stream is combined in an atomization zone with the liquid, e.g., acetic acid, to form an atomized mixture of the gas and liquid. This atomized mixture is then contacted with the second gas stream in a mixing zone within a mixing/separation chamber in which the second gas stream vaporizes substantially all of the atomized liquid, and the resulting mixture of gas, vaporized liquid and residual droplets moves to the separation zone of the mixing/separation chamber. In the separation zone, the residual droplets gravitationally separate from the vaporized mixture, and the vaporized mixture free of a substantial amount of residual droplets is removed from the chamber. A vaporized mixture of carbon dioxide and acetic acid is useful as, among other things, a preservative for perishable products, e.g., baked goods.