Whether you pickup your CO2 from a paintball store, coke distributor, welding supply store, or the guy down the street who refills fire extinguishers, chances are your CO2 has some sort of contaminate. In fact it’s impossible for any substance to be 100% pure, but hey, let’s give it our best shot.
Potential carbon dioxide contamination may include residues which can be carried over from the feed source, from contaminants introduced into the bulk liquid carbon dioxide, or from gas cylinders within the distribution system. Some compounds are of particular concern to beverage manufacturers as they are known to have a negative impact on the flavor and appearance of the beverage. Other compounds that are known to be detrimental to consumer safety are governed by regulatory control. Voluntary quality standards are listed in the ISBT quality guidelines. The industry is also becoming increasingly aware of the serious impact of carbon dioxide impurities on the beverage’s characteristics and the associated consequences of not ensuring its quality. This applies to all sparkling beverages, fountain / post mix as well as beer dispense.
Sources and types of contamination
Understanding the sources of CO2 contamination and the types of contaminants which must be reduced or eliminated is a key factor in achieving acceptable product quality. Prior to delivery, pure CO2 is at risk of contamination from atmospheric air, transportation, storage and handling, which can take place up to several times before reaching the production plant. Types of contaminants include non-volatile organic (NVOR) and non-volatile residues (NVR).
Oil vapor and grease
Atmospheric air contains oil vapor which derives from industrial processes and vehicle exhausts. Other sources of oil and grease are process transfer pumps and compressors. As with other contaminants, oil vapor is drawn into the compressor intake and passes through the intake filter. Typical concentrations can vary between 0.05 and 0.5 mg per cubic metre, but these can increase significantly should the compressor be sited near highways. Additionally, lubricants used in the compression stage of a compressor can also be vaporized and carried over. Once inside the CO2 distribution system, oil vapor will cool and condense into liquid oil.
Flexible hoses and rubber gaskets are typical sources for contaminating CO2 with plasticizer compounds. Liquid CO2 is an effective solvent which can extract plasticizer compounds readily.
Rust and pipescale
Rust and pipescale can be directly attributed to the presence of water in liquid CO2 storage tanks and distribution piping. Over time, the rust and pipescale breaks away to contaminate the CO2.
Typical impurities found in CO2 sourced from fermentation processes and the off flavors associated with them.
Acetaldehyde – Acetaldehyde is present in all beers. Typical ‘apple’ off-flavor at high concentrations.
Di-methyl Sulfides (DMS) – Desirable characteristic of some pale lager beer styles. Typical ‘corn’ off-flavor in some beers.
Benzene – Carcinogenic compound – Regulatory control not detected at low levels by taste or smell.
Iso-Amyl Acetate – Present in most beers. Typical ‘banana’ off-flavors occur at ppm levels.