Keep Cask Ale Fresher for Longer

The RLBS Cask Aspirator, often referred to as a cask breather, is designed to help protect cask-conditioned beer once a cask has been opened. By replacing displaced air with low-pressure CO₂ during dispense, it helps reduce oxidation and maintain beer quality without affecting the traditional character of real ale.

For homebrewers, home bars and beer festivals, a cask aspirator can significantly extend the serving life of a cask, allowing beer to remain in better condition for longer after tapping.

What Does a Cask Aspirator Do?

Every time beer is drawn from a cask, the space left behind must be replaced by something.

In a traditional vented cask, this space is filled by air entering through the spile. While this is part of traditional cask dispense, it also introduces oxygen which gradually affects flavour, aroma and overall beer quality.

A cask aspirator automatically replaces that incoming air with low-pressure CO₂. As beer leaves the cask, the aspirator allows a matching volume of gas to enter, creating a protective blanket above the beer and reducing exposure to oxygen.

The result is beer that stays fresher for longer while retaining the smooth mouthfeel and gentle carbonation expected from cask-conditioned ale.

Designed for Home Cask Ale Systems

In a busy pub, a cask may be sold within a few days of opening.

Most homebrewers don’t have that luxury.

A 4.5 gallon cask contains around 20 litres of beer, while a traditional firkin holds over 40 litres. Without protection, beer quality can begin to deteriorate long before the cask is empty.

A cask aspirator helps bridge that gap, making traditional cask ale more practical for home bars, clubs, festivals and enthusiasts who want to enjoy real ale over a longer period.

Does a Cask Breather Add Carbonation?

No.

This is one of the most common misconceptions surrounding cask aspirators.

Unlike keg dispense systems, a cask aspirator does not force additional carbonation into the beer. Instead, it operates at very low pressure and only supplies gas as beer is removed from the cask.

Its purpose is to replace displaced volume and help protect the beer, not alter its condition.

Why Use a Cask Aspirator?

Protect Beer from Oxidation

Reduces the amount of oxygen entering the cask during dispense.

Extend Serving Life

Helps maintain beer quality for longer after tapping.

Preserve Traditional Character

Maintains the smooth mouthfeel and low carbonation associated with cask ale.

Ideal for Home Bars

Makes serving cask ale at home far more practical.

Works with Traditional Dispense Systems

Suitable for use alongside cask dispense equipment and traditional serving setups.

Perfect For

• Home bar installations
• Real ale enthusiasts
• Homebrew clubs
• Beer festivals
• Traditional British beer styles
• Long-serving cask setups

Key Features

• Low-pressure CO₂ protection
• Helps reduce oxidation
• Extends the life of opened casks
• Suitable for cask-conditioned beer
• Maintains traditional cask ale character
• Ideal for home bars and real ale enthusiasts
• Easy integration into cask dispense systems
• Suitable for pins, firkins and other cask formats

Frequently Asked Questions

What is a cask breather?

A cask breather, also known as a cask aspirator, replaces air entering a cask with low-pressure CO₂ as beer is dispensed.

Will this make my beer fizzy?

No. A cask aspirator does not force carbonate beer. It simply replaces displaced air with low-pressure CO₂.

Do I need a CO₂ cylinder?

Yes. The aspirator requires a suitable low-pressure CO₂ supply to operate correctly.

Can I use this with a 4.5 Gallon BevCask?

Yes. The aspirator can be used with both 4.5 gallon and 9 gallon casks when connected as part of a suitable dispense system.

Is a cask aspirator worth it for homebrewers?

For most homebrewers, yes. Because casks are typically consumed much more slowly than in commercial pubs, an aspirator can help maintain beer quality and make cask ale more practical to serve at home.

What’s the difference between a cask aspirator and a demand valve?

A cask aspirator protects the beer by replacing displaced air with CO₂. A demand valve regulates and controls the gas supply feeding the system. The two products are often used together as part of a complete cask dispense setup.