Commercial refrigeration
How a glycol beer system works and why the beer goes warm
A keg sitting at the right temperature in a cool room can still pour warm beer at the tap. The glycol system decides what happens along that run. When it slips, a venue ends up pouring warm beer in the middle of a Friday night.
6 min read
The short version
Why a cold keg is not enough
The intuitive picture of a draught system is that you keep the keg cold and the beer arrives cold. That holds up over a couple of metres, as long as the keg room sits at the right cool room temperature. Put the keg room any real distance from the bar and it stops working.
A beer line running through a ceiling void or along a back-of-house wall sits in ambient air. In a busy venue on a summer evening that air might be thirty degrees. Beer moving slowly along thirty metres of line picks up heat the whole way and can reach the tap several degrees warmer than it left the keg. Several degrees is enough for a customer to send it back.
An idle tap makes it worse. Beer standing still in a warm line for twenty minutes between pours reaches room temperature, which is why the first pour of a quiet afternoon so often goes down the sink.
A glycol system keeps the entire run cold instead of cooling the beer at either end. The glycol circulates all the time, while the beer only moves when someone opens a tap, so the beer holds temperature whether the bar is flat out or empty.
The four parts of a glycol system
Knowing the name of each part makes any conversation with a contractor a lot shorter. We have fitted glycol systems across around fifteen breweries in Marrickville plus Hawke's Brewery. The same team looks after pub and club dispense systems and cool rooms. Beer and brewery refrigeration covers the brewery side of that work.
- 1
The power pack (glycol chiller)
A refrigeration unit sitting over an insulated bath of glycol solution. It works like any other refrigeration system, with a compressor, condenser and evaporator, except that it cools the bath instead of a room.
- 2
The glycol
Food-grade propylene glycol mixed with water, typically around a third glycol by volume. The mix sets the freezing point, so a technician measures it instead of guessing. Most beverage-grade glycol comes with corrosion inhibitors added to protect the pump and fittings from the inside.
- 3
The python
The insulated bundle running from the keg room to the bar. Inside it sit the beer lines, one per tap, plus a glycol flow line and a glycol return line, all wrapped in foam insulation and an outer sheath. The glycol lines touch the beer lines along the entire length, which is what does the cooling.
- 4
The font and the tap
Plenty of systems fall down on this last stretch. A cooled font circulates glycol up into the tower so the final half metre of line and the tap body stay cold. An uncooled font pours a warm first beer even when the rest of the system works perfectly.
Why the beer went warm
Anything that stops the glycol circulating, stops it being cold or stops it touching the beer lines shows up the same way at the tap. These are the faults venues call us out for most and what each one looks like from behind the bar.
| Cause | What you would notice | Urgency |
|---|---|---|
| Glycol pump stopped | Every tap goes warm over an hour or two. The bath may still be cold with the chiller running normally, which makes it confusing. | Now. Nothing past the keg room stays cold. |
| Low glycol level in the bath | Performance slips gradually, worst on the taps furthest from the keg room. Often a slow leak somewhere on the run. | Same day. Running a pump dry damages it. |
| Condenser blocked with dust | The chiller runs constantly and never quite gets the bath down, especially on hot days. | Soon. It also costs you in power. |
| Python insulation damaged or wet | One section of the run underperforms, often after building work or a leak above the ceiling. Waterlogged foam barely insulates at all. | Within days. It will not improve by itself. |
| Font not cooling | The first pour comes out warm, then the beer runs fine. The classic quiet-afternoon complaint. | Within days. It is a real fault but service can continue. |
| Glycol concentration drifted | Nothing obvious for a long time, then poor performance and eventually corrosion or a seized pump. | At the next service, where the technician checks concentration instead of assuming it. |
What to check before you ring anyone
Two minutes behind the bar makes the call far more useful and occasionally saves it altogether:
- Is the keg itself cold? If the cool room has drifted, the problem is not the glycol system
- Is the chiller running and can you hear or feel the glycol pump?
- Is the glycol in the bath at the mark or well down?
- Is the condenser on the power pack clear or packed with dust and kitchen grease?
- Is it every tap or just some? Some taps points at the python or the font. All taps points at the pump or the bath
- Is it only the first pour? That is the font, not the whole system
- Has anyone worked above the ceiling or in the keg room recently?
Line cleaning and glycol cooling are not the same job
Why glycol systems suit scheduled maintenance
Most of what goes wrong with a glycol system happens slowly. The concentration drifts over years of topping up with water, the condenser clogs a little more every month and the insulation breaks down. Even a pump will often get noisy or run hot for a while before it stops.
It feels sudden because a venue only notices once the system cannot hold temperature through a busy service. By then the fault has usually been building for a season.
Beer systems tend to fall over on Friday and Saturday nights because that is when the load peaks. We take after-hours breakdown calls through our maintenance technician, but a venue on a commercial refrigeration maintenance schedule catches most of those faults on a weekday visit instead.
Common questions
- What is a glycol beer system?
- It is the cooling that keeps beer cold between the keg and the tap. A chiller keeps a tank of glycol and water just below zero and a pump sends it through the insulated bundle that carries the beer lines to the bar. That holds serving temperature over a run of thirty or forty metres, which a cool room alone cannot do.
- Why do beer systems use glycol instead of water?
- The system needs to run below zero without freezing solid. A glycol and water mix freezes at a much lower temperature than water on its own, so the bath can sit below zero and still circulate freely. Beer systems use food-grade propylene glycol.
- Why is my beer pouring warm?
- If the keg is cold, the fault is almost always somewhere between the keg and the tap. The usual causes are a stopped glycol pump, a low glycol level, damaged or waterlogged python insulation, a dusty chiller condenser or a font that is not cooling. A warm first pour that comes good after a pint or two points at the font.
- What temperature should draught beer pour at?
- Most Australian draught beer pours at around 2 to 4 degrees at the tap. Lagers sit at the colder end and some ales a touch warmer, depending on what the brewer intends. The temperature at the point of pour matters more than the keg room reading.