Beer Gas vs CO₂: Which Gas Does Your Keg Need?

Beer gas keeps draught beer moving from keg to tap while helping to preserve the carbonation, flavour and presentation intended by the brewery. The correct choice is not the same for every keg. Most carbonated lagers, ales and ciders use CO₂, while Guinness Draught and other nitrogenated stouts require a nitrogen and CO₂ blend.

This Ireland-focused guide explains beer gas versus CO₂, what 75/25 mixed gas means and how to choose the correct cylinder and regulator. Browse TheKegCru's current beer-gas cylinders, gas refills and gas regulators.

What Is Beer Gas?

“Beer gas” is a broad trade term rather than one universal gas recipe. It can refer to pure food-grade carbon dioxide or to a specified blend of nitrogen and carbon dioxide. In Ireland, a cylinder described as Guinness gas or stout gas normally means 75% nitrogen and 25% CO₂.

Always read the cylinder label and product description. “Mixed gas” without a stated ratio is not enough information to set up a keg correctly.

CO₂ and Carbonated Draught Beer

Carbon dioxide is produced naturally during fermentation and contributes to the carbonation and character of beer. In a draught system, supplied CO₂ enters the keg through the coupler, maintains pressure and pushes beer through the line.

Pure food-grade CO₂ is the normal choice for many lagers, ales and ciders. The correct pressure depends on the beer, temperature, line length, line diameter, cooler and tap. Do not apply a universal pressure simply because two drinks are both lagers.

View our new 10L CO₂ cylinder or 10L CO₂ refill. Check the individual listing for delivery or collection conditions.

What Is 75/25 Mixed Beer Gas?

75/25 mixed beer gas contains 75% nitrogen and 25% carbon dioxide. The order matters: it does not mean 75% CO₂. This blend is used for Guinness Draught and other compatible nitrogenated stouts because it permits the higher dispense pressure needed by a stout tap while limiting the amount of CO₂ applied to the beer.

The nitrogen supports the characteristic tight head and cascading presentation. The CO₂ component helps maintain the beer's intended condition. Pure nitrogen is not the correct substitute for a conventional Guinness Draught keg, and pure CO₂ can overcarbonate the stout and change the pour.

TheKegCru supplies a new 10L 75/25 mixed-gas cylinder and a 10L 75/25 mixed-gas refill for compatible cylinders.

What Gas and Pressure Does Guinness Use?

For Guinness Draught kegs supplied in Ireland, use:

• Gas: 75% nitrogen and 25% CO₂
• Pressure: 35–38 PSI
• Coupler: U type
• Tap: A proper stout tap with a clean restrictor plate

The beer must also be fully chilled and the lines clean. Changing the regulator cannot correct a warm keg, blocked restrictor plate or incorrect coupler. Follow our complete Guinness keg setup guide for the connection and pouring process.

CO₂ vs 75/25 Mixed Gas

Gas	Typical use	Important point
Pure CO₂	Many lagers, ales and ciders	Maintains carbonation and provides dispense pressure; the correct setting depends on the product and system
75% nitrogen / 25% CO₂	Guinness Draught and compatible nitrogenated stouts	For Guinness in Ireland, use 35–38 PSI with the correct U-type coupler and stout tap
Other mixed-gas ratios	Specific brewery-approved products or specialised long-draw systems	Use only when the keg or dispense-system specification calls for that exact blend

Is 50/50 Mixed Gas the Same as Guinness Gas?

No. A 50% nitrogen/50% CO₂ blend is not the same as Guinness gas. Guinness Draught requires the specified 75% nitrogen/25% CO₂ blend in the system described above. Other mixed-gas ratios may be used for particular beers or dispense layouts, but they should not be substituted because a cylinder happens to fit the regulator.

Why the Wrong Gas Causes Pouring Problems

The gas ratio, temperature and pressure work together. If too much CO₂ is applied, beer can become overcarbonated and excessively foamy. If the available CO₂ pressure is too low for the product, beer can lose condition and appear flat. Using the wrong gas can therefore affect flavour as well as appearance.

Before changing pressure, check:

• The exact gas and ratio stated on the cylinder
• The keg's gas and coupler requirements
• The beer temperature from keg to tap
• The condition and diameter of the beer line
• The regulator, connectors and system for leaks
• Whether the correct standard or stout tap is fitted

Choosing a Beer-Gas Regulator

Use a regulator that is designed for the cylinder valve and gas type. A mixed-gas primary regulator controls pressure from compatible mixed-gas cylinders, while CO₂ equipment must be matched to the CO₂ cylinder connection. Do not force incompatible threads or use unapproved adaptors.

The regulator controls pressure; it does not change the gas ratio inside the cylinder. Connecting a 75/25 cylinder to a regulator set for lager does not turn it into CO₂, and changing pressure cannot make the wrong blend suitable for a beer.

Gas-Cylinder Safety

• Keep cylinders upright, secured and away from heat.
• Use them in a ventilated area.
• Do not use damaged, corroded or unlabelled cylinders.
• Close the cylinder before disconnecting equipment and safely release downstream pressure.
• Never apply oil or grease to valves, regulators or fittings.
• Have unfamiliar systems checked by an experienced installer or TheKegCru.

Gas cylinders are pressurised equipment, so delivery and refill options can depend on location and cylinder compatibility. Read the product conditions before ordering or travelling to our Dublin depot at D11 C5DE.

Which Beer Gas Do I Need?

Check the individual keg listing first. For most standard carbonated lagers, ales and ciders, that will usually mean CO₂. For Guinness Draught, use 75% nitrogen/25% CO₂ at 35–38 PSI with a U-type coupler and stout tap. If you are unsure, send TheKegCru the exact beer name, keg size and dispense equipment before connecting the system.