There are two gases used for your keg beers and ciders. Carbon Dioxide (CO2) and Nitrogen (N2). CO2 makes the beer gassy – N2 makes the beer creamy. Think standard Lager vs Stout. These gases are mixed together for the desired result for a particular beer / cider.
If your keg is Tetley’s Smooth flow, John Smith’s Extra Smooth or Guinness then it will have a high concentration of Nitrogen Gas and a low concentration of Carbon Dioxide Gas.
If your keg is a lager or cider such as Carling, Stella Artois or Strongbow, Stella Cidre it will have a very high level of Carbon Dioxide and a very low level of Nitrogen. For these it’s perfectly ok, and gets perfect results, to use 100% CO2 at the correct balance of pressure.
Guinness, Tetley’s Smoothflow and John Smith’s Extra Smooth always use mixed gas of a concentration of 30% Carbon Dioxide and 70% Nitrogen. The mixed gas is supplied pre-mixed together in the same cylinder and we call this a cylinder of ‘30-70 mixed gas’.
It is always best to get advice from your beer keg supplier for more accurate advice.