When beer is bottled, its residual oxygen content of 0.1 mg/l must be kept as low as possible and no more than 0.03 mg/l of oxygen may be absorbed. To this end, breweries employ two different methods, either singly or in combination:
1. Bottles are flushed with CO2 and filled with beer via a long-tube filler. In this case, the filler tube is inserted into the bottle and the bottle is flushed with carbon dioxide before actually being filled with beer. This method consumes a relatively large amount of CO2.
2. Bottles are evacuated and then flushed with CO2. This method greatly reduces carbon dioxide consumption because most of the oxygen is already extracted.