Isobaric (Counter-Pressure) Filling

Isobaric Filling, also called counter-pressure filling, is the standard method for carbonated soft drinks (CSD), beer, and sparkling water. The empty bottle is first pressurised to the same level as the supply tank using CO₂ gas, then filled by gravity. The pressure equalisation prevents the dissolved CO₂ from breaking out of solution during filling. Without isobaric filling, CSDs would foam over (loss of fill volume), lose carbonation, and produce inconsistent fill levels, making BIS audits and consumer experience both unreliable. Typical operating parameters: - Bottle pressure during fill: 3.5–4.0 bar - Filling speed: slower than gravity (CSD 60–90 BPM is comparable to gravity 90–120 BPM) - Filler valves: snift-type (vent residual CO₂ before bottle release) Isobaric fillers are 35–60% more expensive than gravity fillers of equivalent BPM, but mandatory for carbonation > 1.5 vol CO₂.