Extractor hoods and filters: how often, and what happens if you wait

Somewhere around half past nine on a full Saturday, a drop of something amber comes off the edge of the hood and lands on the pass. Someone wipes it with a blue roll and carries on, because there are eleven tickets up and nobody has time to think about the ceiling. That drop is the most honest report you will get all week about what is happening above your burners.

The drop that lands on the pass

Every fryer, flat top and wok burner throws up an aerosol of fat so fine it behaves like smoke. It rides the air straight up. The baffle filters in the canopy are built to make that air change direction hard and fast, so the heavy droplets hit metal and run down into the channel and the little cup at the end. That is the whole trick. It works beautifully, right up until the channels themselves are coated and the air stops turning.

Then the grease keeps going. It lands on the inside of the canopy, on the plenum behind the filters, on the first metre of duct, and in the end it comes back to you as that drop on the pass. Kitchens in Maastricht that run a long lunch and a long evening service, especially the ones down by the Markt with a fryer going from eleven in the morning, reach that point far sooner than anyone expects.

You will usually smell it before you see it. Last night's frying, hanging in the dining room at nine in the morning, is not a ventilation problem. It is a filter problem wearing a ventilation costume.

Why a loaded filter is a fire risk

A clean baffle filter is a set of steel vanes with air gaps. A loaded one is a solid block of fuel, sitting directly above the only open flame in the building, with a warm chimney behind it.

Everybody who has worked a line has seen a pan flare. Oil goes over the edge, the flame jumps, and for a second or two there is fire where your forearm was. With clean filters that flare hits cold metal and dies. With filters that have not been washed in weeks, the flame has something to hold onto, and what it holds onto continues into the plenum where nobody can see it and nobody can reach it. That is the scenario the whole routine exists to prevent. Not a dramatic one. A Tuesday one.

There are duller consequences too, and they arrive sooner. A blocked filter chokes the extraction, so the motor pulls harder for less air, the kitchen gets hotter, the staff get slower, and the smell moves into the dining room. Grease drips onto the salamander and onto plates. And an inspector who sees a hood weeping at the corners does not think about the hood. He thinks about what else is being skipped.

How often, honestly

Nobody can give you one number that fits every kitchen, and anyone who does has not looked at your extraction. What you cook decides it.

Daily, at close: wipe the underside of the canopy and the lip where the drips gather, empty the grease cup or drain tray, and wipe the stainless around the light lenses. It takes a few minutes with a degreaser and a cloth and it is the difference between a filter wash and a filter rescue.

Weekly at minimum, for filters, in any kitchen running a fryer, a chargrill or a wok burner. Busy lines want them more often than that, and plenty of kitchens end up washing a set every night simply because it is easier to do a light one daily than a hard one on Sunday. A kitchen that mostly boils, steams and uses the oven loads its filters more slowly and can stretch the interval, as long as somebody is actually checking rather than assuming.

The check takes five seconds. Drop a filter out and hold it up to the window. If you can see daylight through the channels, it is breathing. If it looks like a solid grey panel, it washes tonight. Weight tells you the same thing — a filter that is noticeably heavier than the spare in the rack is full of what it caught.

Buy a second set. Two sets means service never waits for a drying rack, and the wash happens on a proper rota with dates written down instead of whenever somebody remembers. Write the date on the rota, not in your head.

What washing a filter actually looks like

Gloves on first, because old kitchen grease is alkaline, sharp-smelling and gets under your nails for days. Mark which filter came from which slot if your canopy has an angled end — they are not always interchangeable, and forcing one back in leaves a gap that grease loves.

Drop them into a sink or a tub of water as hot as the tap gives, with a proper alkaline degreaser. Leave them long enough for your coffee to go cold. Soaking does most of the labour; scrubbing a dry filter just polishes the surface and pushes the grease deeper into the channels.

Then a stiff brush, worked along the channels rather than across them, because that is the direction the grease ran when it settled. Rinse hot, both faces. Stand them on edge to drain — never stack them wet, never slide them back damp, because trapped water in a baffle channel sits against the frame and, in a hard-water kitchen, leaves a chalky film that the next lot of grease sticks to happily.

While the filters are out, the canopy is open and that is the moment to use it. Degrease the inside face, the corners, the grease channel and the cup, the light lenses, and the visible face of the plenum behind the filter slots. Finish the outside stainless with the grain, not in circles. That is the part guests see, and it is the part that tells them what the kitchen is like.

One thing a filter is not for: your glasswasher. And harsh caustic detergent in a hot machine will dull and pit aluminium mesh filters until they shed grey powder into the food below. Steel baffles usually survive a pot wash cycle. Mesh generally wants hands, hot water and a brush.

Where we stop and a duct specialist starts

Here is the line, drawn plainly, because a lot of companies leave it vague and let you find out later.

A cleaning team handles the filters, the inside of the canopy, the grease channels and cups, the lights, the stainless, the wall behind the line and the ceiling where the vapour has landed. Everything you can see and reach with an arm and a cloth. That is genuine work and it is most of the fire fuel in a kitchen, because most of it never makes it past the filter bank.

What a cleaning team does not do is the vertical duct, the fan housing and the roof unit. Those need access hatches, hand scraping, the right chemicals in a confined space, and a written report with before and after evidence that your insurer will actually accept. That is a specialist trade, on a different cycle, and a good cleaner tells you when your canopy is clean but the duct behind it is due — rather than quietly wiping the last reachable thirty centimetres and hoping.

If your hood is clean at the filters and the smell in the dining room has not changed, the answer is almost always up the duct.

The part your insurer cares about

Speaking generally, and this is the shape of the thing rather than advice: policies covering commercial kitchens tend to assume the extraction is maintained on a sensible schedule for the type of cooking, and after a fire the question is rarely whether you meant to clean it. The question is what you can show. Your own policy wording decides what applies to you, your insurer or broker is the one to ask, and if a dispute ever goes further than a phone call, het Juridisch Loket is where to start.

Which is the practical reason we work the way we do. Every visit is checked in with an NFC tag on your kitchen wall, so there is a record of who was there and when. The work is photographed, and those photos are reviewed by AI against the checklist for your kitchen before the job is closed — filters out, canopy interior, grease cups, the stainless. So when somebody asks you in six months how often that hood was cleaned, you are not searching your memory. You are opening a log with dates and pictures.

Our team works in English as well as Dutch, and we are insured and registered with the Dutch Chamber of Commerce. We are rated 5.0 on Google. For kitchens that need more than the nightly round — the walls, the ceiling, behind the line, the floor under the fryer — that is a deep clean scheduled outside service hours, and it sits alongside the rest of the commercial work we do across Limburg.

Tonight, before you lock up: drop one filter, hold it to the light, and see what your kitchen has been breathing through.

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