Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is done by removing the moisture component from the liquid solution. The solution, sometimes called an emulsion, is sprayed through a nozzle into a chamber that simultaneously has hot air being blown into it. As droplets of the solution are released through the nozzle and come in contact with the hot air, the moisture content of each droplet is removed, thus turning it from liquid to powder form. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some industrial products such as catalysts. Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.