Snap open a bottle of soda or beer and you will see, hear and feel the familiar fizz and bubbles. These sensations are the result of carbon dioxide (CO2), a colorless, odorless, non-combustible gas. In the beverage industry, CO2 is typically used to carbonate soft drinks and soda water. While the main natural carbonation of beer occurs during the fermentation process, it is necessary to add CO2 to beer after the filtration process to ensure the content is always the same. Beer that is settled may also require forced carbonation prior to bottling.
Adding carbon dioxide to a beverage carries the risk of product contamination with potentially expensive consequences including off-flavors and odors, spoilage, product recalls and damaged reputation.
Sources of CO2 contamination Oil vapour and grease
Atmospheric air contains oil vapour derived from industrial processes and vehicle exhaust. Oil and grease can also emanate from compressors and transfer pumps. This oil vapour is drawn into the compressor intake and moves through the intake filter. Once inside the CO2 distribution system, the oil vapour will cool and condense into liquid oil.
Liquid CO2 is an extremely effective solvent that can easily extract plasticiser compounds from flexible hoses and rubber gaskets.
Rust and pipescale
Rust and pipscale are caused by the presence of water in liquid CO2 storage tanks and distribution piping. Over time, the rust and pipescale breaks away and contaminates the CO2. This can be particularly problematic in older piping systems previously operated with inadequate or no purification equipment.
Typical impurities found in CO2
Typical impurities found in CO2 sourced from fermentation processes and the off-flavours associated with them include:
Acetaldehyde - present in all beers. Typical apple off-flavour at high concentrations.
DMS - desirable characteristic of some pale lager beer styles. Typical corn off-flavour in some beers.
Benzene - carcinogenic compound. Regulatory control not detected at low levels by taste or smell.
Iso-Amyl - present in most beers. Typical banana off-flavours occur at ppm levels.
The consumer experience
Foul taste, odors and off-appearance will also change the way the consumers view the product and may alter their decision to buy more of it — directly impacting the manufacturer’s bottom line. Left unchecked, this can have a dramatic impact on their reputation and success in the market. It is the responsibility food and beverage manufacturers to take appropriate steps to protect the quality of the carbon dioxide and ensure consumers consistently experience a high-quality, desirable product.
CO2 quality guidelines
The International Society of Beverage Technologists (ISBT) is an organization dedicated to the promotion, development, and dissemination of knowledge relating to the art and science of beverage technology. The ISBT has developed quality guidelines to provide guidance for carbonated beverage manufacturers and CO2 suppliers on key characteristics for quality and purity of CO2 when used as a direct food additive in beverages.
CO2 contaminant removal
Traditional methods for CO2 contamination removal consisted of passing the gas through an activated carbon bed. Recent improvements with on-site analytical equipment have revealed that this method cannot maintain the required gas quality.
Working with the International Society of Beverage Technologists (ISBT), to gain a better understanding of the contaminants affecting CO2 and the maximum allowable levels Parker domnick hunter developed a multiple stage purifier that would essentially take out-of-specification, beverage-grade CO2 and bring the quality of gas back within an acceptable quality standard.