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Extraction cleaning - reading the signs
You wipe a surface near the cooking line and it is faintly sticky; a thin greasy film keeps settling on shelves, walls and equipment nearby, no matter how often you clean. That sticky film is airborne grease - grease the extraction is not fully capturing - settling out onto the surfaces around the kitchen. Reading what the film means tells you the extraction is letting grease escape, and why.
The short answer
Sticky surfaces and a thin grease film settling on things near the cooking line mean that airborne grease - grease carried in the air from cooking - is not being fully captured by the extraction, and is settling out onto the surrounding surfaces instead. When the extraction is working well, it draws the greasy air away before the grease can settle; when a film keeps forming on shelves, walls and equipment, it means grease is escaping the extraction and depositing around the kitchen. That points to the extraction not drawing effectively enough - often because grease has built up in the system, reducing the airflow - or to grease getting past the filters. So the sticky film is a sign that the extraction is loaded or under-performing, and that a clean is due to restore its grease capture.
What the film actually is
The sticky film that settles on surfaces near the cooking line is grease - specifically, airborne grease. Cooking, especially frying and grilling, releases grease into the air as fine droplets and vapour, which drift on the air currents in the kitchen. The extraction system exists to capture this airborne grease: to draw the greasy air up into the canopy and away through the ductwork before the grease can settle. When the extraction captures the airborne grease effectively, little settles out, and surfaces stay relatively clean. When some of the airborne grease escapes the extraction, it drifts and settles onto whatever surfaces are nearby - shelves, walls, equipment, worktops - forming the thin, sticky film you notice when you wipe them.
So the film is a physical deposit of the grease the extraction did not capture. Its stickiness is the nature of grease - a thin greasy layer is tacky to the touch, and it holds dust and dirt, which is why surfaces with the film feel sticky and get grubby faster. The fact that it keeps returning, however often you clean, is the key point: cleaning removes the film that has settled, but if the extraction is still letting grease escape, more settles and the film comes back. So a film that keeps reforming is telling you the source is ongoing - the extraction is continually letting airborne grease escape - not that you are not cleaning enough. Reading the film means recognising it as escaped grease, continually resupplied by an extraction that is not fully capturing.
Why grease is escaping
If airborne grease is escaping the extraction and settling as a film, the question is why the extraction is not capturing it - and the common answer is that the extraction is under-performing, usually because it is loaded with grease. When grease has built up in the system - on the filters, in the ductwork, on the fan - the airflow drops, and a weaker airflow captures less of the airborne grease, letting more escape into the kitchen to settle. So the film is often a downstream sign of grease build-up in the system: the accumulated grease reduces the airflow, the reduced airflow captures less grease, and the uncaptured grease settles as the film. The build-up and the film are connected.
There can be other contributors too - filters that are not capturing well, whether through being greased up or poorly specified, letting grease past; a system drawing less air than it should for its cooking load; or gaps in how the greasy air is captured at the canopy. But whatever the specific cause, the film points to the same conclusion: the extraction is not capturing the airborne grease as it should, and grease is escaping into the kitchen. And since grease build-up in the system is the most common reason for reduced capture, the film is frequently a sign that the system is loaded and due a clean. Reading the film as a sign of under-capture points you to checking and cleaning the extraction to restore its ability to draw the greasy air away.
More than a cleaning nuisance
It would be easy to treat the sticky film as just a cleaning nuisance - something to wipe away and forget. But reading it as a sign is more useful, because it points to two things worth knowing. First, that the extraction is not capturing grease as well as it should, which usually means the system is loaded with grease and under-performing - the same build-up that reduces the airflow and lets smoke linger. So the film is one of several signs, alongside lingering smoke and stale smells, that together indicate a system loaded with grease and due a clean. Read together, these signs make a clear case for having the extraction cleaned.
Second, the film is a visible reminder that grease is escaping the extraction and depositing around the kitchen - which has hygiene implications, since grease-filmed surfaces hold dust and dirt and are harder to keep clean, and can affect the impression of the kitchen. So the film matters both as a diagnostic sign of the extraction's state and as a hygiene issue in its own right. Both point to the same action: restoring the extraction's grease capture by cleaning the system, so the airborne grease is drawn away rather than escaping to settle. Dealing with the film at source - by fixing the extraction that is letting the grease escape - is more effective than endlessly wiping the surfaces it settles on, because it stops the film reforming rather than just removing it each time.
What to do about it
The practical response to a persistent sticky grease film is to address the extraction that is letting the grease escape, rather than only cleaning the surfaces the film settles on. Cleaning the surfaces is necessary for hygiene, but on its own it is a losing battle - the film keeps reforming as long as the extraction keeps letting grease escape. So the more effective step is to have the extraction system checked and cleaned: removing the grease that has built up in the filters, ductwork and fan restores the airflow, which restores the system's ability to capture the airborne grease and draw it away before it settles. With the capture restored, less grease escapes, and the film reforms far more slowly, if at all.
This is why the film is worth reading as a sign and acting on at source. It is telling you the extraction is under-capturing - usually because it is loaded with grease - and the fix is to clean the system so it captures properly again. If the film persists even after cleaning, that points to something in how the greasy air is being captured - the canopy, the airflow, the filter specification - which may need looking at, but for most kitchens a film that has crept in over time is a sign of a system that has loaded with grease and needs cleaning. Restore the extraction's capture, and you deal with the film at its source - the sticky surfaces clear and stay clearer, because the grease is being drawn away rather than escaping to settle on them.
The takeaway
A sticky film that keeps settling on surfaces near the cooking line is airborne grease - grease from cooking that the extraction is not fully capturing, settling out onto shelves, walls and equipment instead of being drawn away. The film keeps returning however often you clean because the source is ongoing: the extraction is continually letting grease escape. And the usual reason it is under-capturing is that it is loaded with grease - the build-up reduces the airflow, the weaker airflow captures less, and the uncaptured grease becomes the film. So the film is a downstream sign of grease build-up in the system.
That makes the sticky film worth reading as a sign, not just wiping away as a nuisance. It points to an extraction that is under-capturing and usually loaded with grease and due a clean - one of several signs, with lingering smoke and stale smells, of a system that needs cleaning. The effective response is to fix the capture at source: have the extraction cleaned to remove the grease and restore the airflow, so it captures the airborne grease properly again and the film stops reforming. Cleaning the surfaces alone is a losing battle; cleaning the extraction deals with the film at its source. So read the film as escaped grease, and address the extraction that is letting it escape.
Questions
It is airborne grease - fine grease droplets and vapour released by cooking - that the extraction has not fully captured, settling out onto surfaces near the cooking line. When the extraction captures the greasy air well, little settles; when a film keeps forming, grease is escaping the extraction and depositing on shelves, walls and equipment.
Because the source is ongoing. Cleaning removes the film that has settled, but if the extraction is still letting grease escape, more settles and the film returns. A film that keeps reforming tells you the extraction is continually under-capturing - it is not that you are not cleaning enough, but that the grease is being continually resupplied.
Most commonly because it is loaded with grease and under-performing. Grease built up on the filters, in the ductwork and on the fan reduces the airflow, and a weaker airflow captures less of the airborne grease, letting more escape to settle. So the film is often a downstream sign of grease build-up reducing the system's capture.
Yes. A grease film is sticky, holds dust and dirt, and makes surfaces harder to keep clean, which affects hygiene and the impression of the kitchen. So it matters both as a diagnostic sign of the extraction's state and as a hygiene issue in its own right - both pointing to restoring the extraction's grease capture by cleaning the system.
Address the extraction that is letting the grease escape, not just the surfaces it settles on. Cleaning the surfaces is a losing battle while the extraction keeps under-capturing. Having the system cleaned removes the grease, restores the airflow and restores the capture, so grease is drawn away rather than escaping to settle - and the film reforms far more slowly, if at all.
That points to something in how the greasy air is being captured - the canopy design, the airflow, or the filter specification - which may need looking at. But for most kitchens, a film that has crept in over time is a sign of a system that has loaded with grease and needs cleaning, and restoring the capture by cleaning deals with it.
A sticky grease film means the extraction is not capturing grease as it should - our cleaning removes the build-up and restores the airflow, so grease is drawn away rather than settling on your surfaces.
