Your customers will tell you before your thermometer does. Pints start pouring foamy. The lager’s not cold enough. Cask ale loses its condition halfway through the cask. By the time someone actually goes down to the cellar and checks the temperature, the damage to stock quality has been underway for hours.
Cellar cooling is one of those systems that works quietly in the background until it doesn’t — and then it becomes the most expensive problem in the building. Wasted beer, unhappy punters, and a phone call to the brewery that nobody wants to make.
Why Temperature Matters This Much
Different products need different temperatures, and getting it wrong affects every pint you pull:
- Cask ale: 11–13°C. Too cold and the flavour flattens out. Too warm and it conditions too fast, goes lively, and starts fobbing at the tap.
- Keg lager and cider: 3–5°C. Needs to be properly cold for a clean, tight pour.
- Stout on nitro: 6–8°C. Slightly warmer than lager to get the right creamy texture.
Most pub cellars target a compromise around 11–12°C, with the python (the insulated bundle of lines running from cellar to bar) providing additional chilling for products that need serving colder.
Temperature swings are just as bad as a consistently wrong temperature. A cellar that bounces between 8°C at night and 16°C during a busy Saturday creates havoc with cask conditioning and causes excessive fobbing at every tap.
The Symptoms
You don’t always need to check the thermometer to know something’s off:
Foamy pints. Excessive fobbing is usually the first indicator. Warm beer releases dissolved CO₂ faster when it hits the glass, creating more foam than the pour should produce. If your fob-to-pour ratio suddenly jumps, check the cellar before you blame the line clean.
Flat cask beer. Cask ale that’s gone flat or lost its condition has been too warm for too long. The secondary fermentation that gives cask its character speeds up with heat, and the cask blows through its natural carbonation faster than it should.
High wastage. If your weekly wastage numbers are creeping up and nothing else has changed — same cleaning schedule, same gas pressure, same pour technique — the cellar temperature is the next thing to check.
Warm kegs to the touch. Walk into the cellar and put your hand on a keg. If it doesn’t feel distinctly cold, the room’s not doing its job.
What Goes Wrong
Condenser Problems
The cellar cooler works like any refrigeration system: it absorbs heat from the cellar air and rejects it somewhere else, usually via a remote condenser on the roof or an outside wall. If the condenser is blocked with dust, leaves, moss, or bird debris, it can’t reject heat efficiently. Head pressure rises, cooling capacity drops, and the cellar temperature starts climbing.
Roof-mounted condensers in London take a beating from the weather and the wildlife. We’ve pulled pigeon nests out of condensers, scraped moss off coil fins, and cleared years of accumulated grime from units that hadn’t been serviced since installation.
The fix is condenser cleaning — and making sure it happens regularly, not just when the cellar overheats.
Refrigerant Leak
If the cellar cooler has gradually lost performance over weeks or months — maintaining 12°C last winter, struggling at 14°C in spring, hitting 18°C now — the refrigerant charge is almost certainly dropping. Slow leaks on cellar coolers often happen at pipe joints, especially where the indoor unit connects to the remote condenser via copper pipework running through the building.
Under F-Gas regulations, the leak has to be found and fixed before we recharge. We carry leak detection equipment on every van.
Thermostat and Controller Faults
The cellar cooler’s thermostat tells the system when to run and when to stop. If it fails or reads incorrectly, the system either runs non-stop (driving the cellar too cold, icing up cask ale and causing its own fobbing problems) or doesn’t run enough (letting the temperature drift up).
Some pub cellar coolers use simple mechanical thermostats that drift with age. Others use digital controllers that can lose their calibration or develop sensor faults. Either way, if the controller’s not reading the actual room temperature accurately, the system can’t maintain the right conditions.
Insufficient Capacity
This one’s not a fault — it’s a design problem. The cellar cooler was sized for the cellar as it was originally configured, and things have changed since then. More stock stored in the cellar generating thermal mass. A bigger glass washer installed that throws heat. The cellar door left open more often because it’s being used as a thoroughfare.
In some cases, the pub itself has expanded — more taps, more kegs, more throughput — and the cellar cooling system was never upgraded to match. The unit runs flat out and still can’t hold temperature on a warm Saturday afternoon.
Poor Insulation
A cellar with poor insulation is a cellar that gains heat from every direction. Warm air from the pub above coming through an uninsulated ceiling. Heat from a boiler or hot water pipes running through the cellar. Sunlight hitting an exposed external wall.
Some pub cellars are naturally cool — stone-built basements that barely shift in temperature year-round. Others are converted ground-floor rooms with single-brick walls and no insulation. The cooling system has to overcome whatever heat gains the building allows in, and in a poorly insulated space, that can be a losing battle.
Maintenance Keeps It Running
A cellar cooler that’s serviced twice a year — condenser cleaned, refrigerant pressures checked, thermostat calibrated, electrical connections tested — will run reliably for years. The ones that get forgotten about until July, when the cellar hits 20°C and the wastage goes through the roof, are the expensive ones.
We also check the cellar environment during a service visit: door seals, insulation condition, heat sources that shouldn’t be there, airflow around the evaporator. The cooler is only half the equation — the cellar itself needs to give the system a fighting chance.
Cellar Cooling Down? Call Us
If your cellar’s warming up and the pints are suffering, call us on 020 3974 1419. We install, maintain, and repair cellar cooling systems across London’s pubs, bars, restaurants, and hotels. F-Gas certified, fast response, and we understand that when the cellar goes down, every hour matters.