Beer, the cellar, keg changing and gas safety

A keg is a pressurised steel barrel. Gas pushes the beer out through a coupler on the keg, along a python of insulated lines cooled by a remote cooler, to the fount and tap. Lager and ale use CO2 or a 60/40 mix; stout uses mixed gas (typically 70% nitrogen, 30% CO2) which gives the tight head and surge. The cellar is kept at 11–13°C and the beer is chilled again at the fount. Wrong gas or wrong pressure means flat or fobbing beer and wasted stock.

1. Close the gas valve on the coupler (or the line) and let the pressure in the coupler release.
2. Disconnect the coupler: pull the handle up (or turn, depending on type) and lift it off. Hang it, don't drop it on the floor.
3. Move the empty aside using a keg trolley or by rolling on its rim. Never lift a full keg alone: a full 50-litre keg weighs around 60kg, a 30-litre around 40kg.
4. Check the new keg: right beer, in date, seal intact. Wipe the keg neck. Fit the coupler square and lock it down.
5. Open the gas slowly. Listen and smell for leaks. Pull the first half-pint through at the bar and check it.
6. Date and initial the keg. Record the change if the venue logs it (most tills can).

Carbon dioxide is heavier than air, colourless and odourless. A leak in a closed cellar pools at floor level and displaces oxygen; the first signs are headache, dizziness and shortness of breath, and people have died in Irish pub cellars from it. The HSA's keg cellar guidance: keep the cellar ventilated; fit a CO2 or oxygen-depletion alarm, installed and maintained by a competent person; store cylinders upright and secured with a chain while in use; stack no more than two kegs; use trolleys; wear safety footwear; keep the hatch closed when unattended and the stairs sound. The eight-hour occupational exposure limit for CO2 in Ireland is 5,000 ppm (0.5%).

If the alarm sounds or you feel light-headed in the cellar: get out, keep others out, ventilate from outside, and call the gas supplier. Do not go back in to find the leak.

1. Close the cylinder valve fully. Vent the regulator.
2. Unscrew the regulator connection (left-hand thread on some; don't force it).
3. Unchain the empty, mark it empty, chain the full one upright in its place.
4. Check the washer, fit the regulator, open the valve slowly and check the gauges and for leaks with leak-detection spray or soapy water. Never use a flame.
5. Set the pressure to the brewery's figure for that beer and line length; don't guess.

• Clean lines every seven days with the approved cleaner at the right dilution, flush thoroughly, and log it. Dirty lines are the single commonest cause of a bad pint and of 'off' complaints.
• Check the cellar and fount temperatures daily. Guinness's own guidance is to serve its draught stout at around 6°C using the two-part pour: glass at 45°, fill to three-quarters, let it settle, then top up with the tap pushed back to form the dome.
• Rotate stock first in, first out; check best-before dates on every delivery.
• A keg that fobs, pours flat or tastes sour: check gas, temperature and date before you blame the brewery, and keep the keg for the rep to see.