Draught Beer: How Does It Work?

Draught beer, also spelt 'draft', is beer served from a cask or keg rather than a bottle or can. The usual spelling is 'draught' in the UK, Ireland, Australia, and New Zealand, and 'draft' in North America. In any draft system, there are six main components: a cooler, keg, coupler, gas, tubing, and faucet. The airtightness of a keg is important to keep the beer from becoming flat and flavourless. The gas used is typically carbon dioxide or nitrogen, which is fed into the keg at a constant rate to maintain pressure and push the beer out.

Draught beer is served from a cask or keg

A cask has a tap hole near the top edge and a spile hole on the side used for conditioning the unfiltered and unpasteurised beer. Beer is served directly from the cask, either by gravity or with the help of a beer engine. Cask ale, or beer served directly from a cask, is making a comeback, with aficionados praising its full and nuanced flavour.

Kegs, on the other hand, are made of stainless steel and are more durable and portable. They have a single opening at the centre of the top, where a flow pipe is attached. Gas flows in and beer flows out through this opening. Inside the keg is a long metal tube called a spear, which reaches almost to the bottom. When pressure is applied to the top of the liquid inside the keg, the beer is pushed up through the spear and out through the tap.

The gas used to pressurise the keg can be carbon dioxide, nitrogen, or a blend of the two. Carbon dioxide works well, but too much can make the beer overly fizzy. Nitrogen is less soluble in beer and helps maintain the natural carbonation without affecting the flavours and aromas.

Keg beer is artificially carbonated

To understand how keg beer is artificially carbonated, it is important to know the basic components of a draft system: the cooler, keg, coupler, gas, tubing, and faucet. The keg, which can vary in size, shape, and material, is where the beer is stored and kept cold to maintain freshness and prevent spoilage. The coupler, also known as the party pump, connects the gas and beer lines to the keg, allowing gas pressure to push the beer out of the keg and through the tubing to the faucet.

In the context of artificial carbonation, the gas used is typically pure bottled carbon dioxide (CO2) or nitrogen. The gas cylinder is connected to the keg, and the gas pressure is adjusted using a regulator to control the amount of pressure entering the keg. The gas flows into the keg through the gas post, which is one of the two posts on a Cornelius keg, the other being the liquid post. By applying gas pressure to the top surface of the liquid, the beer is pushed up through a metal tube called the dip tube and out through the liquid line.

To achieve artificial carbonation, there are two main methods: force carbonation and natural carbonation. Force carbonation, also known as "force-carbing," involves infusing CO2 directly into the beer from a gas cylinder. This method is faster and has less room for error compared to bottle carbonation. The key steps include preparing the gas and liquid lines, adjusting the gas pressure, and allowing the beer to carbonate for a specified period.

Natural carbonation, on the other hand, involves feeding leftover yeast additional sugars to naturally create CO2 within the keg. This method takes longer and may result in a cloudier beer due to the presence of yeast.

The choice between force carbonation and natural carbonation depends on various factors, including the desired level of carbonation, the beer style, and personal preference. Additionally, temperature plays a crucial role in achieving the desired CO2 volumes, with lower temperatures requiring less CO2 pressure to reach the desired carbonation level.

Cask ale is unpasteurised and unfiltered

The term "real ale" was coined by The Campaign for Real Ale (CAMRA) to describe draught cask beer. CAMRA was founded in Britain in 1971 to promote and advocate real ale, distinguishing it from bland, highly carbonated, mass-produced beer. The campaign has been a success, with over 200,000 members across the UK. Cask ale is now almost universally available and sought after in British pubs.

Cask ale is unpasteurised, which means it has not been heated to a temperature of over 60°C for between 25 to 30 minutes to eliminate microorganisms. While pasteurisation helps to preserve beer, it is believed to damage the beer's natural taste, colour, and aroma. Unpasteurised beer is said to have a rounder and more complex flavour.

Cask ale is also unfiltered. Unfiltered beer is opaque, with a spectrum from hazy to milky. Unfiltered beer is also more flavourful, as the finings used to clear beer of yeast before serving also bind with proteins and hop oils and remove flavour from the beer.

Kegs are made from stainless steel

There are different grades of stainless steel, such as 304 and 316, which have different properties and are used for different applications. Stainless steel is an ideal material for kegs because it is strong enough to withstand the pressure required to dispense the beer and resistant to corrosion and tarnishing.

Some older kegs may be made of aluminum, which is lighter and less sturdy than stainless steel. Aluminum kegs are typically imported and not as common as stainless steel kegs. They can be identified by their whitish color and lighter weight.

The choice of material for kegs is an important factor in ensuring the quality and longevity of the beer. Stainless steel kegs have become the industry standard due to their durability, ease of maintenance, and ability to maintain the integrity of the beer.

Beer taps control the release of beer

Beer taps are an essential component of any draught beer setup, allowing the controlled release of beer from its container. The tap is a valve, specifically designed to regulate the flow of beer from the keg or cask. The term "tap" is almost universally used for this purpose, although other terms such as "faucet", "valve", or "spigot" may be used for similar valves in different contexts.

The process of tapping a keg involves connecting the tap to the keg and building pressure to force the beer out. The tap consists of a pump, a hose, and a handle. The bottom of the tap connects to the top of the keg, with the tap's hose linking to the keg's metal ring. Once the tap and keg are securely turned and locked into place, the handle is pushed down and pumped to begin the flow of beer.

The science behind the tap's functionality lies in the pressure exerted on the beer's surface, forcing it upwards through a long metal tube called a "spear" that extends from the valve to the bottom of the keg. This pressure can be created by external carbon dioxide or nitrogen cylinders, which push the beer out with gas pressure. Alternatively, simpler methods like party pumps or hand pumps can be used to manually pump air into the keg, although this can cause faster spoilage due to the presence of oxygen.

The type of tap and the amount of pressure applied depend on various factors, including the temperature of the beer, the elevation, and the desired level of carbonation. For example, warmer temperatures in the cooler require more pressure to maintain carbonation. Additionally, the distance the beer has to travel from the keg to the tap can impact the applied pressure and the need for chilled tubing to keep the beer cold during its journey.

In summary, beer taps play a crucial role in controlling the release of beer from kegs or casks. The process involves connecting the tap, building pressure, and regulating the flow to achieve the desired pour. The specific techniques and equipment used can vary, but the underlying principle of managing pressure remains fundamental to serving draught beer.

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