If your drinks keep tasting “off,” losing their fizz too quickly, or pouring inconsistently, the problem may not be your equipment or the product. In many cases, the real cause is CO₂ contamination – and most operators don’t even realise it’s happening.
CO₂ contamination is common, completely invisible, and one of the biggest hidden threats to beverage quality. Drinks can pick up sulphur smells, chemical notes, flatness, or foam instability long before anyone suspects the gas supply. Even certified beverage-grade CO₂ can carry impurities that slip through the supply chain unnoticed.
Because CO₂ becomes part of the drink itself, any contamination has a direct and immediate impact on flavour, aroma, carbonation, and presentation. It’s a silent issue that affects breweries, bars, restaurants, and soft-drink systems every day – often without a clear explanation.
Understanding how CO₂ becomes contaminated is the first step to preventing it. Once you know where impurities enter the gas, you can stop them before they ever reach the glass.
What Is CO₂ Contamination?
CO₂ contamination happens when unwanted chemicals, gases, or physical particles enter the carbon dioxide used to carbonate or dispense drinks. These impurities are often microscopic and impossible to detect visually, yet they have a powerful effect on how beverages taste, smell, and behave. In the beverage industry, CO₂ contamination refers to any impurity that disrupts the flavour, aroma, carbonation stability, foam retention, or shelf life of a drink.
Definition for the Beverage Industry
In beverage production and draught dispense, CO₂ contamination means the CO₂ supply contains unwanted chemical, physical, or gaseous impurities. These include:
- Sulphur compounds such as hydrogen sulphide (H₂S)
- Carbonyl sulphide (COS)
- Aromatic hydrocarbons
- Moisture and water vapour
- Oil droplets from compressors
- Oxygen and other reactive gases
- Particulates from cylinders, fittings, or pipelines
Even trace levels – measured in parts per million – can cause noticeable defects. Because CO₂ becomes part of the drink itself, any impurity in the gas directly affects the finished beverage.
Why Clean CO₂ Is Essential for Drinks
Clean CO₂ is vital because it influences every sensory and structural part of a beverage. When CO₂ is contaminated, drinks suffer in multiple ways:
- Flavour: Impurities can introduce bitter, chemical, plastic, or sulphurous notes.
- Aroma: COS and H₂S produce burnt or rotten-egg smells that overpower natural aromas.
- Carbonation: Contaminants interfere with CO₂ absorption, leading to flat or inconsistent fizz.
- Foam retention: In beer, impurities break down foam proteins, causing the head to collapse quickly.
- Shelf life: Moisture and oxygen accelerate oxidation, making drinks stale far sooner than expected.
If the CO₂ isn’t clean, the drink isn’t clean – no matter how perfect the recipe, cellar temperature, or line hygiene. This is why understanding CO₂ contamination is so crucial for protecting beverage quality from production to dispense.
The Main Sources of CO₂ Contamination
CO₂ contamination can happen at any stage of the gas supply chain. From the moment CO₂ is captured to the moment it reaches your beverage system. Understanding where these impurities come from helps explain why drinks can taste wrong or behave unpredictably, even when suppliers provide certified beverage-grade CO₂.
1. CO₂ Production & Capture
The contamination process often begins at the source. CO₂ is typically captured from:
- Fermentation
- Combustion processes
- Industrial manufacturing byproducts
These environments naturally contain impurities such as:
- Carbonyl sulphide (COS)
- Hydrogen sulphide (H₂S)
- Hydrocarbons
- Oxygen and nitrogen carryover
Even in small amounts, these compounds can dramatically affect beverage aroma, flavour, and carbonation stability.
2. Refining & Purification Limitations
After capture, CO₂ goes through refining to remove impurities. However, purification systems vary between suppliers, and not all of them fully eliminate problem gases.
Key issues include:
- Beverage-grade standards allow trace impurities
- Refining processes often struggle to remove COS
- Hydrocarbons can persist even after scrubbing
- Moisture levels may remain above ideal sensory thresholds
This means that gas leaving the production plant can be compliant, but still far from clean on a sensory level.
3. Compression & Liquefaction
During compression or liquefaction, CO₂ can pick up additional contaminants from the equipment used in the process:
- Oil traces from compressors
- Moisture pickup if systems aren’t fully dry
- Lubricants or seal residues introduced through mechanical wear
These contaminants are easy to miss during supplier testing but very noticeable once the gas enters your drink.
4. Tanks, Pipelines & Transport
The journey from the gas producer to your venue introduces more contamination risks. CO₂ often travels through:
- Bulk tanks
- Pipelines
- Tankers
- Intermediate storage vessels
Common contamination sources include:
- Corrosion on steel surfaces
- Rust particles
- Environmental contamination during transfers
- Moisture ingress from temperature swings or poorly sealed connections
None of these contaminants are visible when the cylinder arrives – but they affect your drink the moment the gas enters the system.
5. Cylinder Filling & Storage
Cylinders are reused many times. If they aren’t cleaned thoroughly between fills, contamination builds up.
Key risks:
- Residue from previous fills
- Particulates trapped inside older cylinders
- Poor valve hygiene due to handling
- Warm or humid storage conditions introducing moisture
A single contaminated cylinder can destabilise carbonation and introduce off-flavours across an entire system.
6. On-Site Equipment Issues
Even if the CO₂ arrives clean, it can become contaminated inside your own venue.
Common on-site causes include:
- Moisture in regulators
- Contaminated or poorly maintained gas lines
- Leaks that allow oxygen or environmental air into the system
- Improper cylinder handling that introduces dust or particulates
This is why CO₂ needs to be cleaned at the point of use, not just at the supplier.
The Contaminants Commonly Found in CO₂ (Even When Beverage-Grade)
Even when CO₂ is certified as beverage-grade, it can still contain impurities that affect the flavour, aroma, and carbonation of drinks. These contaminants are often present in trace amounts (far below safety limits) yet still strong enough to alter the sensory quality of a beverage. Understanding these impurities is essential for diagnosing problems and protecting product consistency.
Hydrogen Sulphide (H₂S)
Hydrogen sulphide is one of the most recognisable contaminants due to its strong “rotten egg” smell. Even tiny concentrations can overpower a drink’s natural aroma and leave customers questioning its freshness. This compound is a common byproduct of fermentation and combustion processes, making it difficult to remove completely during CO₂ capture.
Carbonyl Sulphide (COS)
COS creates burnt, chemical, or sulphurous notes that linger in both beer and soft drinks. It is one of the hardest contaminants to eliminate and can pass through refining systems unnoticed. COS is a major cause of “chemical” off-flavours in beverages, and many operators only discover its presence after testing or filtration.
Aromatic Hydrocarbons
Aromatic hydrocarbons can introduce plastic, oily, or solvent-like flavours. Because they dissolve into beverages easily, even low levels can distort taste. These impurities often enter CO₂ during compression or cylinder filling, especially when equipment is ageing or poorly maintained.
Moisture
Moisture in CO₂ reduces carbonation stability and encourages staling. In beer, moisture also affects foam formation and retention. High moisture levels are usually caused by poor storage practices, humidity during transport, or inadequate drying during gas production.
Oil & Particulates
Oil droplets, rust particles, or dust can enter CO₂ during compression, cylinder refilling, or pipeline transport. These particles may not directly affect flavour, but they cause operational issues such as clogged regulators, pressure instability, and irregular carbonation behaviour.
Oxygen
Oxygen is a common contaminant in CO₂ supplies and a major contributor to oxidation. It accelerates staling, dulls flavours, and reduces shelf life. Even a small amount can significantly affect beer, cider, and sparkling beverages.
Why These Impurities Pass Through the Supply Chain
Despite strict regulations, contaminants still enter the CO₂ supply chain for several reasons:
- Specification limits allow it: ISBT and EIGA standards set maximum thresholds – but those thresholds still permit detectable contamination.
- Testing isn’t continuous: Suppliers test batches, not every cylinder, meaning variations go unnoticed.
- Contamination reoccurs in transit: Rust, moisture, oil, and particulates can enter CO₂ during transport, pipeline transfers, or cylinder filling.
The result is a gas that meets certification requirements but fails sensory expectations. This is why point-of-use CO₂ polishing is essential for beverage quality.
How to Detect CO₂ Contamination
CO₂ contamination is invisible, but its effects are not. You can often spot the signs long before you confirm the source. By combining simple sensory checks with system diagnostics and occasional gas testing, you can identify CO₂ issues early and prevent them from affecting drink quality.
Sensory Checks
Your senses are often the first and most reliable detection tool. Contaminated CO₂ leaves clear clues:
- Smell: Sulphur-like, burnt match, plastic, or chemical aromas often point to COS, H₂S, or hydrocarbon contamination.
- Taste: Drinks may develop a bitter edge, metallic note, or strange chemical aftertaste.
- Foam behaviour: In beer, contaminated CO₂ destabilises foam proteins, leading to weak, thin, or rapidly collapsing heads.
If your drinks suddenly smell odd, taste “off,” or lose carbonation too quickly, CO₂ contamination is a likely cause.
System Diagnostics
Dispense systems also reveal contamination through irregular behaviour:
- Pressure instability: Fluctuating or “surging” pressure can indicate moisture or particulates in the gas.
- Inconsistent pours: Flat one minute, foamy the next — a hallmark of gas quality issues.
- Unexpected carbonation swings: CO₂ may not dissolve properly if impurities interfere with absorption.
When system performance changes without an obvious cause, the CO₂ supply is often the missing link.
Gas Purity Testing
If sensory or system checks suggest a problem, CO₂ purity testing can confirm it. Options include:
- Portable CO₂ analysers: Quick, on-site checks for contaminants and moisture.
- Inline monitoring systems: Continuous readings of gas quality entering the beverage system.
- Gas chromatography (laboratory testing): The most accurate method for detecting COS, H₂S, hydrocarbons, and oxygen.
Testing becomes particularly important after supplier changes, equipment upgrades, or repeated customer complaints.
Supplier Documentation (COA)
Your CO₂ supplier should provide a Certificate of Analysis (COA). This document lists the purity levels and contaminants detected in a batch of gas. It is useful — but limited:
A COA shows:
- Test results at the supplier’s plant
- Compliance with ISBT/EIGA specifications
A COA does not show:
- Whether the gas stayed clean during transport
- Whether impurities entered during cylinder filling
- How the gas behaves once inside your system
This is why you should never rely solely on supplier certification. Clean CO₂ must be confirmed – and protected – at the point of use.
How to Prevent CO₂ Contamination in Beverage Systems
Preventing CO₂ contamination is far easier and far cheaper than fixing the problems it creates. A few consistent practices can protect every drink you serve and ensure your gas supply stays clean, stable, and neutral.
Use ISBT/EIGA-Compliant Suppliers
Start with suppliers who follow recognised CO₂ purity standards.Always:
- Request Certificates of Analysis (COAs) for each batch
- Check for variations between deliveries
- Confirm the testing date and method used
- Ask specifically about COS, H₂S, and hydrocarbon removal
While compliance doesn’t guarantee perfect purity, it reduces the risk of serious contamination.
Install a CO₂ Polishing Filter
A CO₂ polishing filter is the most effective way to prevent contamination at the point of use. This ensures any impurities picked up during production, transport, or storage are removed before the gas enters your drinks.
Sure Purity’s Carboguard systems provide industry-leading protection:
Carboguard Mini — ideal for bars, pubs, fast-food and restaurant dispense
Carboguard Craft — engineered for breweries and production facilities
All of our Carboguard systems remove:
- Carbonyl sulphide (COS)
- Hydrogen sulphide (H₂S)
- Aromatic hydrocarbons
- Moisture and trace oils
Benefits include cleaner flavour, brighter aroma, more stable carbonation, and more consistent pours across every keg, BIB, or batch.
Maintain Clean Gas Lines
Clean CO₂ is only effective if the delivery pathway is also clean. Focus on:
- Keeping regulators dry and free from oil or lubricant residue
- Preventing moisture buildup in connectors and hoses
- Running regular leak checks to stop oxygen entering the system
- Replacing worn seals and washers before they fail
Good gas hygiene and clean lines protects both product quality and equipment reliability.
Store Cylinders Correctly
Cylinder storage has a direct impact on CO₂ purity.
Always store cylinders:
- Upright to prevent valve contamination
- In cool, dry conditions to reduce moisture ingress
- Secured to prevent damage or valve impact
- Away from chemicals or odours that may migrate through fittings
Small storage errors often lead to large quality problems.
Test CO₂ Regularly
Routine testing helps catch issues early. Use:
- Portable CO₂ analysers for quick checks
- Inline monitors to track purity in real time
- Gas chromatography (GC) for precise lab analysis
Test after supplier changes, equipment upgrades, pressure irregularities, or repeated customer feedback.
CO₂ Contamination vs CO₂ Polishing – The Key Difference
Many operators rely on beverage-grade CO₂ because it meets industry specifications. But in real beverage systems, specification limits are not the same as sensory purity. This is what makes polishing essential.
Beverage-Grade Still Allows Contaminants
Beverage-grade CO₂ can legally contain:
- COS
- H₂S
- Hydrocarbons
- Moisture
- Oxygen
- Particulates
These levels pass compliance testing – but they do not guarantee clean flavour, stable carbonation, or predictable dispense performance.
Polished CO₂ Is “Sensory Clean”
CO₂ polishing removes the impurities that cause flatness, harsh aromas, and chemical off-notes. The result is gas that is:
- Sensory neutral
- Consistent from cylinder to cylinder
- Optimised for flavour, aroma, and foam stability
- Safe for both production and dispense
It’s the only way to ensure CO₂ behaves correctly in real operating conditions.
Predictable Gas Behaviour
With polished CO₂, operators notice:
- More stable fizz and carbonation retention
- Stronger, longer-lasting beer foam
- Reliable pressure performance
- Uniform pours across shifts and staff
- Fewer unexpected quality issues
Polished CO₂ behaves the same every time – and that reliability is what protects beverage quality from source to glass.
Final Thoughts
CO₂ contamination is far more common than most operators realise. It is invisible, unpredictable, and easy to overlook – yet it remains one of the biggest causes of flat, inconsistent, or off-tasting drinks. Even when suppliers provide beverage-grade CO₂, the gas can still carry trace impurities that affect flavour, aroma, carbonation, and foam.
Beverage-grade CO₂ meets a standard, but it does not guarantee the sensory purity required for high-quality drinks. True protection only comes from cleaning the gas at the point of use. By polishing CO₂ before it enters your beverage system, you remove the sulphur compounds, hydrocarbons, moisture, and particulates that silently damage drink quality.
Polishing CO₂ protects more than flavour. It safeguards your equipment, reduces waste, stabilises carbonation, and protects the reputation of your venue or brand.
Contact us and discover how Sure Purity’s Carboguard systems remove CO₂ contaminants and ensure clean, consistent gas for every drink you serve.
