Draught Equipment and System Configuarations > Equipment and Configurations for Long-Draw Draught Systems > Gas
Topics in this section include:
Gas Blenders
Nitrogen Generators
Gas Filters
Nitrogen Gas (N2)
Blended Gas Bottles
To push beer across the distances found in long-draw systems usually calls for gas pressures well above what is needed to maintain beer carbonation levels.
Most long-draw systems employ a nitrogen-CO2 blend to prevent over-carbonation of the beer. The exact blend needed will depend on the system parameters and operating pressure. The correct blend might be purchased pre-mixed or custom blends can be mixed onsite from separate nitrogen and carbon dioxide sources. The use of custom gas blends brings new equipment into play, including nitrogen generators and gas blenders.
Pre-mixed cylinders containing a mix of between 70-75% nitrogen and 30-25% CO2 are intended for use with nitrogen-infused beers or “nitro” beers. These blends are not intended for use with regularly carbonated beers (those with more than 2.0 volumes or 3.9 grams/liter of CO2), even in high-pressure long-draw systems. Use of “nitro” beer gas on regular beers causes the beers to lose carbonation in the keg, resulting in flat beer being served within three to five days. The flat beer is most noticeable near the end of the keg with the amount of flat beer increasing the longer the beer is in contact with this gas. Similarly, straight CO2 should not be used to dispense nitro beers.
Straight CO2 should only be used in a long-draw system when ideal gauge pressure is sufficient to produce the proper flow rate and there is absolutely no temperature increase in the draught lines outside the cooler. Since ideal dispense pressure with straight CO2 is relatively low, even a slight temperature increase from the keg cooler to the draught line can allow the CO2 to escape from the beer in the draught line, causing foamy beer at the tap.
In some long-draw systems gas plays an entirely different role, powering beer pumps used to move the beer.
Gas Blenders
Single Blend - Blender (left) and Double Blend - Mixer (right)
Gas blenders mix pure tank CO2 and pure tank nitrogen to a specified ratio. Blenders can be ordered to specific ratios and often provide two blends: one for ale/lager and one for nitrogenated beers. Recommended features for a gas blender include:
- Output mix is preset by the manufacturer and is not adjustable on site.
- Blender shuts down when either gas supply runs out, preventing damage from running on only one gas.
- Blender produces two blends so that both “nitro” and regularly carbonated beers can be served. The blend for regularly carbonated beers can adequately serve products with a reasonable range of CO2 volumes (e.g. 2.2-2.8 volumes of CO2).
Nitrogen Generators
Nitrogen Generator (left) and Nitrogen Generator w/blender (right)
Nitrogen generators extract nitrogen from the atmosphere. Air is supplied by either a remote or integrated air compressor. Nitrogen generators are typically equipped with a built-in gas blender.
To protect nitrogen purity from compromising draught beer quality, nitrogen generators should have the following features:
- Produce nitrogen with a purity of at least 99.7%.
- Have air inlets equipped with both an oil/water filter and a sterile air filter.
- Use “oil-free”-type air compressors
All nitrogen generator filters should be inspected and replaced according to the manufacturer’s specification.
Gas Filters
Gas Filter
Beverage grade CO2 comes from many commercial and industrial operations and is supplied for many uses beside beverages. (i.e., fire extinguishers, welding, food processing, etc.) CO2 bottles can be contaminated by poor handling and storing. They can be contaminated by beer or soft drinks if a check valve malfunctions and the beer or soft drink flows back into an empty CO2 bottle. A gas filter helps safeguard beer by removing unwanted impurities or contaminants from the gas. Filters must be replaced periodically per manufacturer’s instructions.
Nitrogen Gas (N2)
Nitrogen gas (N2) is blended with CO2 to aid in dispensing beers in systems requiring delivery pressures above CO2 equilibrium. Nitrogen is not easily absorbed by beer. As an inert gas, it does not degrade the flavor of the beer, making it perfect for blending with CO2. The blend of gases is one option for dispensing beer over long distances without over-carbonating the beer in the keg. Blended gases are also necessary for dispensing nitrogenated beers.
Blended Gas Bottles
Blended gas bottles are vendor-mixed CO2 and nitrogen gas mixes. These blends are typically available in blends of approximately 75% nitrogen 25% CO2, used to dispense nitrogenated beers. In some markets, blends of approximately 60% CO2 40% nitrogen may also be available as a premix and custom blends may be ordered from some vendors.
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