Alcoholic Seltzer Filling: CO2, Low-O2 and Flavour

Views: 145 Author: Howie SUN Publish Time:
A CSD line is judged by the CO2 left in the sealed bottle, not by the volumes set at the mixer, and the gap between the two is where most projects lose money.

Aluminum Can Filling Machine for Hot-fill Juice and Tea Drinks

Key facts at a glance
Filling methodIsobaric, CO2 counter-pressure
Rated output12,000-36,000 BPH at 0.2-2 L
ContainersPET bottle, glass bottle, aluminum can
CO2 handlingPre-pressurisation and return pipe, no venting
ValvesMechanical, semi-electric or volumetric
Line scopeWater treatment, syrup mixing, carbonation, filler, pack

Why does carbonated product need isobaric filling?

A carbonated drink is a saturated solution held in equilibrium by pressure and temperature. If the filler exposes it to atmosphere, CO2 leaves the liquid as foam and the fill level collapses. Isobaric filling pressurises the bottle to the bowl pressure first, fills under counter-pressure, then releases in a controlled ramp.

Mechanical, semi-electric or volumetric valves: what is the difference?

Mechanical valves open and close on a fixed cam profile and are the most forgiving on maintenance. Semi-electric valves use a signal to open and close, so the fill window can be set per recipe. Volumetric valves dose a chamber and hold accuracy when bottle pressure or product temperature drifts during the shift.

Valve typeSettingBest for
MechanicalFixed cam profileSingle product, long runs
Semi-electricSignal-timed open and closeRecipe changes within one product family
VolumetricChamber dosePressure or temperature drift during the shift
Isobaric + volumetricChamber dose under counter-pressureHigh CO2 with tight fill accuracy

The Isobaric Filling Machine for CSD and Sparkling Water is the matching unit when this becomes a line project.

How do you size a CSD line without oversizing the CO2 plant?

Size the filler on peak shift demand with a production factor of 0.65-0.85, then size the CO2 supply on average consumption, not peak. A CO2 plant built for the filler nameplate runs partly loaded for most of the year and loses more gas to vaporisation than the line saves in speed.

Site requirements, air and water consumption sit with the CSD & Sparkling Water by Mechanical Filler.

How does a can line differ from a PET line for CSD?

A can is filled and seamed, a PET bottle is filled and capped. Cans run faster per unit and are counted in CPH; PET allows larger formats and a lighter package. The filler principle is the same isobaric one, the closing equipment and the line rate are not.

The same question is worked through from another angle in How Nitrogen Dosers Preserve Flavor in Carbonated Beverages.

How to read the numbers. The BPH figures quoted are reference ranges on the product specification. A rated BPH is measured at one CO2 level and one temperature; format changes and CIP sit outside it, so size on 0.65-0.85.

Frequently asked questions

What CO2 level can an isobaric filler hold?

It holds what the mixer sets and the temperature allows. Most CSD runs between 2.5 and 4.0 volumes, with the target set per product. Retention, not the mixer set point, is what the acceptance test should measure in the filled bottle.

How many cans per hour is 24,000 CPH?

400 cans per minute. CPH and BPH are different units and cannot be compared directly, because can and bottle formats carry different volumes and different downstream equipment.

Does a CSD line need a nitrogen doser?

It is used where the package needs internal pressure support or low oxygen, for example in cans and in some PET formats. It is an option, not a default, and it adds a consumable cost per 1,000 units.

Can a CSD line fill glass bottles?

Yes, with a different infeed, spacing and capping set. Glass needs mechanical spacing rather than an air conveyor, and the filler runs at 4,000-20,000 BPH on glass against 12,000-36,000 BPH on PET.

Key takeaways
  1. Carbonation is a pressure and temperature problem before it is a valve problem.
  2. Judge a CSD line on CO2 retention in the filled bottle, not on the mixer set point.
  3. Size the CO2 plant on average demand, not on the filler nameplate.
  4. Warm product loses CO2 before the filler can dose it.
About the author
Written by the Sunswell engineering team - led by Howie SUN, Founder & CEO, with 14 years in filling and blow-moulding equipment R&D and turnkey project delivery across 71+ countries.
Last reviewed: 2026-08-28 . Reviewed by Sunswell engineering team
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