Draught / Draft Beer: The Complete Guide for Bar Professionals

Few things in a bar are judged as quickly as a pint of draught beer. Guests see the colour, the head and the first sip, and within seconds they know whether the venue takes its beer seriously. What they never see is everything behind the tap: the cold room, the gas, the lines, the cleaning schedule and the pouring habits of the team.

This guide walks through the whole chain, from the meaning of the word itself to the last drop in the glass, so that bartenders, supervisors and F&B managers can serve beer that is cold, fresh and consistent. The infographic at the bottom of the page summarises everything on one poster that you can download for your training room or bar back office.

Draught vs Draft: What Is the Difference?

The two spellings cause more debate than they deserve. Draught is the traditional British spelling and is common in the UK, Europe and India. Draft is the American spelling used in the USA and Canada. Both are pronounced “draft”, and both mean exactly the same thing: beer served from a keg or cask through a tap, rather than poured from a bottle or can.

The important point for bar professionals is what the word does not tell you. It says nothing about quality. A draught beer can be a craft ale or a mass-market lager, pasteurised or unpasteurised, excellent or poor. What decides quality is freshness, temperature, gas pressure, clean lines and good pouring. A well-maintained system can make beer taste fresher than the same brand from a bottle, because it is served straight from a cold, sealed vessel. A neglected system does the opposite.

Keg or Cask: Types of Draught Beer Storage

Draught beer reaches the glass from one of two vessels.

Keg (the most common). A keg is a sealed stainless-steel container connected to a CO₂ system and kept under pressure. Beer in a keg is usually filtered and carbonated at the brewery, so it stays consistent from the first pour to the last and keeps well when stored cold. Kegs suit bars, restaurants and hotels because they are easy to handle, stack and rotate.

Cask (the traditional vessel). A cask is common in the UK. Cask beer is naturally carbonated by a secondary fermentation inside the cask, and it is usually served through a hand pump or by gravity at cellar temperature rather than ice cold. It is a living product that needs skilled cellar work, and it should be sold within a few days of being tapped.

Keg sizes vary by region, so always check the label before ordering or connecting a coupler. Smaller kegs are a smart choice for slower-selling beers, because a keg that is finished sooner stays fresher.

How a Draught System Works, Step by Step

Every draught system, from a single-tap bar fridge to a hotel with forty taps, follows the same logic: gas pushes beer from the keg to the faucet. Six parts do the work.

1. CO₂ cylinder. Stores food-grade CO₂ at high pressure, typically 800–1,000 psi at room temperature. Because the CO₂ inside is mostly liquid, the cylinder gauge stays steady until the cylinder is almost empty, so weigh the cylinder if you want to know how much is left.
2. Regulator. Reduces the cylinder pressure to a safe working pressure, usually in the region of 10–14 psi for standard kegs. Most regulators carry two gauges: one for the cylinder and one for the line.
3. Gas line. Carries the regulated CO₂ from the regulator to the keg coupler.
4. Keg coupler. Locks onto the keg valve and separates the two paths: CO₂ goes in as gas, beer comes out as liquid.
5. Beer line. Carries beer from the keg to the tap. Its length and diameter create resistance, which slows the flow so the beer arrives at the faucet calmly rather than in a rush.
6. Tap or faucet. Opens to dispense the beer into the glass.

The result is a pressurised system that pushes beer from keg to tap, keeps CO₂ dissolved in the beer while it travels, and delivers a fresh, chilled, properly poured glass. Change any one part of that chain, such as warm beer, low pressure or a dirty line, and the guest notices in the glass.

The Science of CO₂ Carbonation

Carbonation is simply CO₂ dissolved in beer. Under pressure and at low temperature the gas dissolves into the liquid, and a small share of it reacts with water to form carbonic acid (CO₂ + H₂O ⇌ H₂CO₃). This is what gives beer its bubbles, its lively mouthfeel, a gentle crispness on the palate and the rising stream of aroma that guests notice on the first sip. Cold beer absorbs CO₂ far more easily than warm beer, which is why temperature control matters so much.

There are two ways beer gets its carbonation:

• Natural carbonation. Yeast produces CO₂ during fermentation and the gas is trapped in the beer. It is common in traditional brewing and cask ales, and gives a softer, more natural carbonation.
• Forced carbonation. Finished, chilled beer is exposed to CO₂ under controlled pressure. It is fast, consistent and widely used by modern breweries, and it is how most commercial kegs are carbonated.

Most lagers and ales sit between roughly 2.2 and 2.8 volumes of CO₂, while stouts and cask ales carry less. Stouts served on nitro use a different gas: a blend of nitrogen and CO₂, often called beer gas, at higher pressure and pushed through a restrictor plate in the faucet to create the creamy, cascading head.

Factors That Affect CO₂ Dissolution

Six variables decide how much gas stays in the beer. Understanding them is the difference between guessing and controlling your pour.

• Temperature. Colder beer holds more CO₂. A fridge that drifts upwards makes the beer foam.
• Pressure. Higher pressure increases dissolution, and lower pressure lets the gas escape.
• Contact time. The longer the beer and gas stay in contact, the more CO₂ dissolves. A keg left at the wrong pressure for days slowly changes.
• Beer style. Each style is brewed to a target carbonation level, so a wheat beer and a stout should never share the same setting.
• System design. Line length, line diameter, lift and equipment quality all affect resistance and flow.
• Altitude. Higher altitude lowers atmospheric pressure, so venues in the hills usually need slightly higher regulator pressure.

Recommended Pressure Guide by Beer Temperature

The table below shows the approximate regulator pressure needed to hold about 2.4 volumes of CO₂ in a typical lager or ale at each beer temperature.

Notice how quickly the number climbs: roughly one extra psi for every degree Celsius. That is why a stable, cold keg room does more for beer quality than any adjustment on the regulator. For most standard lagers and ales held at 3–4°C, the working pressure is around 10–11 psi. Treat the table as a general guide only. Adjust for the beer style, your dispensing height and system design, and always follow the brewery’s own recommendation for the beer you are serving.

Beer-Line Balancing

A balanced system gives the right flow rate and prevents excess foam. The principle is simple: the total resistance of the beer line should match the pressure applied to the keg.

Total resistance = (line length × resistance per metre) + vertical lift + faucet resistance

Resistance per metre depends on the line material and inside diameter, so use your line supplier’s chart. Here is an illustrative example. Suppose the keg runs at 12 psi, the faucet adds about 2 psi, and the tap sits 1 metre above the keg, which adds roughly 1.6 psi of lift. The line therefore needs to supply about 8.4 psi of resistance. A 6 mm (¼-inch) vinyl line offers roughly 2.8 psi per metre, so around 3 metres of line would balance the system.

• More line length means more resistance.
• If resistance is too low, beer pours too fast and foams.
• If resistance is too high, beer pours slowly.
• Never simply raise the keg pressure to fix a slow pour. Over time that over-carbonates the beer and creates a new foam problem.

Why Does Draught Beer Become Foamy?

Foam is the most common complaint in any bar, and it almost always traces back to temperature, pressure or dirty lines. Work through this checklist before blaming the keg.

If a keg has just been changed, expect a little foam on the first pours as air clears from the line. Pour and discard until the beer runs smoothly.

Draught Line Cleaning Process

Beer lines are a perfect place for yeast, bacteria and beer stone to grow, and the result is off-flavours, foam and unhappy guests. A regular clean protects taste, hygiene and the equipment itself.

1. Disconnect the keg. Shut off the gas, release the pressure and remove the coupler.
2. Circulate cleaning solution. Pump an approved line cleaner through the lines and faucet for the contact time the manufacturer specifies.
3. Rinse with clean water. Flush until no cleaner or taste remains. Test strips are a simple way to confirm the rinse is complete.
4. Sanitise as required. Follow the instructions of your cleaning product; some need a separate sanitising step and some do not.
5. Reconnect the system. Fit the keg, restore the gas and pull a test pour before service.

Frequency. Clean lines every one to two weeks, or as your brewery or equipment maker advises. The benefits are better taste, less foam, no off-flavours, improved hygiene and longer equipment life. Many venues also run an acid clean now and then to remove beer stone.

Safety and records. Line cleaners are strong chemicals. Wear gloves and eye protection, never mix products, and keep a simple cleaning log that shows the date, the product used and who did the work. That log is also useful evidence during a food-safety audit.

Correct Pouring Technique

Even a perfectly balanced system can be spoiled in the last five seconds. Teach the same seven steps to every bartender.

1. Use a clean, beer-clean glass. Rinse it in cold water; a clean glass sheets water evenly rather than beading.
2. Hold the glass at about 45 degrees.
3. Open the faucet fully. A half-open faucet causes turbulence and foam.
4. Let the beer flow down the side of the glass.
5. Straighten the glass gradually as it fills.
6. Finish with the correct head, about two fingers deep for most styles.
7. Close the faucet completely, and never let the faucet touch the beer or the glass.

Good rotation matters too. Use first-in, first-out on kegs, respect the brewery’s best-before date and record the date each keg is tapped. Fresh beer poured well is the simplest form of quality control a bar has.

Serving Temperature, Glassware and Keg Handling

Temperature deserves its own checklist because it touches every other topic in this guide. Keep the keg room or cooler steady, typically around 2–4°C, and make sure the beer stays cold all the way to the faucet. Long runs of line between the cooler and the tap warm up during quiet periods, so keep them short or use a cooled line. Serving temperature then depends on the style: lagers are usually served colder than ales, while cask ale is traditionally served at cellar temperature.

Glassware matters just as much. Wash beer glasses separately from greasy tableware, air-dry them and store them clean. A frosted glass may look impressive, but ice crystals cause foam and numb the flavour, so a cool, clean glass is a better choice. Finally, handle kegs gently. Rough handling or long rolling shakes up the beer, so let a moved keg rest before you tap it and always use the correct coupler for the keg type.

CO₂ Safety in the Cellar

CO₂ is invaluable in a draught system, but it is also an asphyxiant. It is heavier than air and can collect in low, poorly ventilated cellars after a leak.

• Store and use cylinders upright and secured with a chain or bracket.
• Keep cellars and gas rooms well ventilated.
• Install a CO₂ monitor in enclosed cellars and test it regularly.
• If an alarm sounds or someone feels dizzy, leave, raise the alarm and ventilate. Do not enter to help without proper equipment.
• Have cylinders changed by trained staff, and check regulators and hoses for leaks.

Key Takeaways

• Draught means draft: same meaning, different spelling.
• CO₂ keeps the keg under pressure and pushes beer from keg to tap.
• Carbonation is CO₂ dissolved in beer, controlled by temperature and pressure.
• Temperature is one of the most important factors in every pour.
• Balanced beer lines give the best pour.
• Clean lines and clean equipment are essential.
• Correct pouring technique makes a big difference.
• Follow the beer style and the brewery’s recommendations.
• Handle and store CO₂ cylinders safely.

Frequently Asked Questions