Changing a keg at a bar without wasting beer or gas
Changing a keg looks simple: unclip one, clip on the next. Done badly, it costs a litre or more of beer in foam, leaks gas through worn seals and puts a warm keg on line in the middle of service. Done well, it takes two minutes and wastes almost nothing. Here is the routine we teach bar teams.
The new keg must be cold before it goes on
The most common keg change mistake happens hours before the change. A keg delivered at 30 °C and put on line the same evening will pour foam. Warm beer cannot hold its CO2 at normal serving pressure, so gas breaks out in the line and the glass fills with froth.
A full 50 litre keg can take 24 hours or more in a cold room to come down to 2 to 4 °C. Plan the cold room so the next keg of every tap is already cold. Rotate stock first in, first out. Put the delivery date on each keg with a marker.
Check the gas before you touch the keg
Look at the cylinder contents gauge or weigh the cylinder before you start. A keg that ran dry at the same moment as the gas leaves you guessing which one is empty. If the cylinder is low, change it first: close the cylinder valve, back off the regulator, swap the cylinder, check the washer on the regulator inlet, then open the valve slowly.
Spray the regulator joint with soapy water after any cylinder change. Bubbles mean a leak. A slow leak at a single fitting can empty a cylinder over a weekend.
The two minute change, step by step
- Confirm which keg is empty by lifting it. An empty keg is obvious by weight.
- Lift the coupler handle to the off position, then twist or slide the coupler off the keg.
- Look at the coupler seal and probe. A cracked, flattened or missing washer is the main cause of leaks at the keg.
- Spray the top of the new keg's spear with clean water or a food safe sanitiser and wipe it. Dust and spilt beer collect there.
- Fit the coupler to the new keg and press the handle fully down.
- If the line has a foam on beer detector, vent and reset it. Our guide to foam on beer detectors explains how.
- Pour a small test into a jug until clear beer runs, then taste it before serving.
Where the beer is lost
Beer is lost at three points in a keg change. First, the last pour from the old keg turns to foam as gas enters the line. Second, after the new keg goes on, that foam has to be pushed out of the line before clear beer flows. Third, a warm or badly seated new keg pours foam for minutes.
On a short line, the loss may be a few hundred ml. On a long draw system where each line holds 70 ml per metre, foam can fill several metres of tube. That is why long draws benefit most from foam detectors and why staff should never pour foam into customer glasses to save it.
A simple habit helps more than any gadget: change the keg the moment the tap starts to splutter, not after three more attempts to squeeze out a pint. Each extra attempt pushes more gas into the line and adds to the foam that has to be cleared later.
Where the gas is lost
Gas loss is less visible but just as real. The usual culprits are worn coupler washers, loose hose clips, a regulator joint not tightened after a cylinder change and couplers left connected to gas with no keg attached. Most modern couplers have a non return valve on the gas side, but it is not a reason to leave a coupler hanging open.
Do a soapy water check on every gas joint once a week. It takes five minutes. A single slow leak can cost more in gas each month than a full set of new washers.
Know your coupler type
Kegs reach Indian bars from many suppliers, so one bar can end up with more than one coupler type. Forcing the wrong coupler onto a keg damages seals and can injure staff. Keep spare couplers of each type you use, labelled. Make sure everyone knows which keg needs which. Our guide to keg couplers and fittings covers the common types.
Never try to open or repair a keg spear. It is under pressure and should only be serviced by the brewery or keg supplier.
Taste the first pour from every new keg
The jug test after a change is a quality check too. A new keg can be a new batch. If it tastes different from the last one, that is worth knowing before the customer tells you. Stale, papery notes may mean a keg that sat warm in transport. A sour or buttery edge may point to the line rather than the beer.
Write each keg change down: date, time, tap, batch and who changed it. That log turns arguments into answers when a beer goes wrong.
Your first step: before tonight's service, walk the cold room and check that the next keg for every tap is already cold. Put any warm keg at the back with the delivery date on it.
Common questions
How long should a keg sit in the cold room before tapping?
A full 50 litre keg can take 24 hours or more to cool from Indian room temperature to 2 to 4 °C. Plan stock so the next keg is always cold.
Why does a new keg pour foam?
Most often the keg is still warm, the coupler is not fully engaged or foam from the old keg is still in the line.
Should I turn off the gas when changing a keg?
Not usually. Lift the coupler handle to the off position before removing it. Close the cylinder valve only when changing the gas cylinder itself.
