The Oxford Companion to Beer definition of

draught beer.

Draught Beer. Beer racked into kegs and served on draught (also spelled “draft” in the United States) is generally considered to be the optimal method to showcase the brewer’s art. In the United States, draught beer generally is not pasteurized and is ideally maintained cold through distribution from brewery to glass (although some brewers now choose to flash pasteurize and forego refrigeration). Modern single-valve stainless cooperage—coupled with state-of-the-art cleaning and filling systems—allows beer to be aseptically packaged with very little oxygen pickup or ingress. The stainless keg eliminates degradation from light, as well as potential oxygen ingress through bottle cap seals or flavor influence from can liners that is possible with other beverage packaging methods. When dispensed through a properly maintained and balanced draught system, this allows for optimal brewery-fresh beer to be delivered to the glass. Although draught beer has the potential to deliver the best drinking experience, it can easily be ruined with improper storage and handling through a poorly designed or poorly maintained dispensing system or improperly cleaned glassware. The draught system should be designed and balanced to deliver a perfect pour from the first serving to the last glass. Today’s wide range of available beer styles and installation configurations dictate that someone knowledgeable about dispensing system design and the styles of beer to be served is involved in the set-up and balancing of the system to ensure that the brewery’s desired gas makeup, carbonation level, and serving temperature are maintained. While it can be excellent, British traditional cask-conditioned ale, sometimes referred to as “draught beer” in the UK, is an entirely different system which we do not address here. See cask conditioning and real ale.


Modern kegs are almost entirely fabricated from deep-drawn stainless steel and available in a range of common US and European sizes: 7¾ gallons (1/4 bbl) to 15.5 gallons (1/2 bbl) and 20, 30, or 50 liters (5, 8, or 13 gal). Breweries make significant investments in kegs, and they can last for many years. If properly maintained, they can be refilled hundreds of times; but due to theft and unscrupulous metal scrapping, a large percentage of kegs never make it back to the brewery. Marginally successful attempts have been made to fabricate kegs from less expensive coated mild steel, plastic, or “bag-in-a-box” technology, but currently none of these protect the quality of the beer as well as stainless steel. Although several variations exist worldwide, modern keg designs utilize a double-ported top valve that supplies both the dispensing gas and the tapping connection. The valve is connected to a down tube, or spear, that extends to within a 1/4” (7 mm) of the bottom and allows the complete emptying of the keg. During the cleaning and filling cycle at the brewery, the keg is inverted and multiple cycles of detergent, water, and steam are pumped at high pressure through the same fittings before filling.

Keg Delivery and Storage

Kegs of beer should be stored and delivered cold—as close to the dispense temperature as practical. Depending on the temperature, it will take many hours—or even days—to cool a warm keg. Most dispensing and foaming problems are caused by attempts to dispense warm beer. Gas pressure, temperature, and system design are all closely interrelated. Tapping a keg even a few degrees above the desired typical 34°F–38°F (1.1°C–3.3°C) temperature specification for most American beer styles may cause excessive foam and difficulty in pouring. While it is possible to run draught lines at warmer temperatures in order to show certain beers at their best, this requires very careful design and balancing.

Dispensing Gas

Although most beer is carbonated and dispensed utilizing pure carbon dioxide gas, the use of mixed gas blends containing carbon dioxide (CO2) and nitrogen (N2) are becoming commonplace—allowing greater dispense system design and flexibility. Remote cold boxes are often utilized to allow easier delivery, loading, and greater keg storage than may be available in a crowded bar or restaurant. The increased pressure required to deliver beer these greater distances would over-carbonate the beer if 100% CO2 were used, but the low solubility and inert nature of N2 make a blend of the two gases ideal. Due to oxidation concerns, air should never be used to dispense beer. In the past, some draught-system suppliers marketed air compressors as a way to save money on CO2 or mixed gas. The oxygen in the air rapidly degrades the beer; unfortunately, such systems are still in use. (Inline beer pumps may also be used to boost the beer-line pressure without changing the carbonation level). Nitrogenated beers (such as some styles of stout) require a higher blend of N2 and CO2 to allow proper balance. Several premixed bottled blends are available; or a gas blender can be purchased to mix the two gases on site. Care must be exercised when selecting gas blends so the beer doesn’t over-carbonate or lose carbonation during the dispensing period. The dispense gas pressure is reduced using a gas regulator that is set to the equilibrium pressure of the beer in the keg. Beverage regulators must contain a safety relief valve to relieve dangerous system pressure in case of a regulator malfunction.

Dispensing System Design

A properly designed draught system should maintain the brewer’s desired carbonation level and gas balance, provide for the appropriate dispensing temperature for the style of beer, allow for a pour rate of approximately 2 ounces (60 ml) per second, and deliver the amount of foam desired. Depending on the installation constraints and physical layout of the system, several different draught-system technologies have evolved; but many components are common to all designs. Best practices call for all-metal system components that come in contact with beer to be made of stainless steel. Chrome-plated brass was commonly used due to its lower cost and ease of manufacture, but the acidic nature of beer and the chemicals utilized in routine draught line cleaning attack the brass and will lead to metallic off-flavors and increased difficulty in cleaning and maintaining good system hygiene. Tubing and other plastic components need to be manufactured of food-grade, approved materials. During installation and design of any dispensing system, the style of beer, CO2 content, temperature, and elevation are factored in to balance the system for a perfect pour. The simplest—and often best-designed systems—are called “direct draw.” Here the keg is located in a cold box either directly behind or below the faucet or “tap.” It is important that the lines and fittings are kept chilled to the dispensing temperature to prevent foaming. The keg is tapped using a dual-ported “coupler” that mates up to the top of the keg; this supplies both the dispense gas and beer outlet connection. The coupler also contains a secondary safety relief valve that will relieve potentially explosive pressures in case of a regulator malfunction. The coupler is connected using a short length of vinyl tube with a stainless “tail piece” that connects the coupler and “shank” that goes through the cold box wall or bar “tower” mounting the dispensing faucet. When the distance from the keg to a remotely mounted tap increases—up to a maximum of about 25 feet—chilled forced air is employed in a duct surrounding the beer line to maintain the beer and faucets at or below the cold box temperature to prevent foaming. Long-draw installations are possible—with the kegs being located up to several hundred feet from the faucet utilizing heavily insulated glycol-chilled bundles, or “trunk” lines. These can contain any number of beer lines—surrounding two or more supply-and-return chilled glycol lines—through which refrigerated food-grade glycol is continuously circulated from the cold box to the tap, to maintain the beer at the correct dispensing temperature. Although the use of chilled long-draw systems allows greater design flexibility when situating the cold box and faucets, the added distance complicates system cleaning and increases beer loss. Although not ideal, for temporary 1-day events and picnic use, hand pumps, or “jockey boxes,” can be used with either cold plates or coils to chill the beer on the way to the tap; or the keg can be iced down in a large tub. Since hand pumps introduce oxygen, the kegs with them will not keep for more than a day or two after being tapped.

System Cleaning

One of the keys to quality draught beer is a clean and well-maintained dispensing system. Although beer will not harbor pathogens, many common strains of bacteria can grow and taint or sour a poorly maintained draught system. Cleaning should be performed at 2-week intervals, using industry-accepted detergents at proper concentrations and temperatures. The system should first be flushed with cold water to remove any residual beer; then detergent should be circulated for a minimum of 15 minutes—or if no pump is available, soaked for 20 minutes. The faucets and coupler should be hand cleaned, and then the entire system completely flushed with potable cold water before use.

See also dalton’s law.


Ken Grossman