In a kitchen, a ventilation system that incorporates extraction of hot, dirty air and its replacement by a supply of clean air is not an optional extra but a legal requirement. Health and safety regulations insist on kitchens being well ventilated and comfortable to work in.
A ventilation system removes heat and grease coming from cooking equipment, steam from dishwashing and boiling, and dangerous carbon monoxide fumes produced from the burning of gas. Simply opening a window or door doesn't give adequate ventilation, and it provides a means of access for airborne insects.
There are two main types of kitchen ventilation - canopy or ventilated ceiling - and canopies are the most popular in commercial kitchens. Both types use a system of filters and fans to exhaust the heat, dangerous gases and humidity, while trapping particles of food and fat debris and introducing cleaned and cooler air into the kitchen.
It is now a requirement to have the gas supply to the cooking range interlocked with both the extract and supply air systems. This automatically switches off the gas supply should a fire occur in the extraction canopy through a build-up of fat. Most fire-suppression systems use chemicals that are activated automatically in the event of a fire in the ventilation system.
There are six types of grease filter available:
These are layers of metal mesh on to which the grease particles are deposited as they are drawn through the system. They require regular washing, are not efficient at removing high levels of grease and, in a high-fat kitchen, can pose a fire risk in the extraction system.
This type of filter should be used only where there will be little or no grease held in suspension within the exhaust gases. So these filters should not be installed above deep-fat fryers, chargrills, griddles, salamander grills or bratt pans used for shallow-frying. Cleaning of these filters is done by soaking them in very hot water with a degreasing detergent, although this will eventually destroy the internal mesh and the filter will need to be replaced.
These are more efficient than mesh filters, as they work by forcing the air to change direction and velocity, which separates the grease from the airstream, with the deposited grease running off into collection troughs. This type of filter is suitable for general cooking with moderate grease-load applications. These filters should be manufactured only from stainless steel. Cleaning procedure is simple, as they can be washed in a commercial dishwashing machine.
Cartridge filters should not be confused with disposable filters, as disposable filters should never be used in commercial kitchen-extract systems. Cartridge filters are made from stainless steel and are more efficient than baffle filters, as they are intended for moderate to heavy grease-load applications. This type of filter is cleaned, like a baffle filter, by running it through a commercial dishwashing machine.
This is a more advanced cartridge system, where the filters are subject to an automatic internal washing cycle to clean them, usually at the end of the working day. They need a hot water supply and are among the more expensive systems, but are very good at extracting grease.
Continuous water mist
Regarded as one of the most effective grease-extraction systems, but requires plumbing and is expensive. There is a continuous mist of cold water sprayed into the extraction system that emulsifies fat and causes it to drop into a collection trough.
The latest technology for the efficient elimination of grease from kitchen ventilation systems is the combination of cartridge filters and ultraviolet UV-C light. This will give grease- and odour-removal efficiencies in excess of 98%.
Cleaning of extraction systems is essential on both hygiene and fire safety grounds. If there is a high level of frying in the kitchen, the essential cleaning may be as frequent as weekly. The kitchen designer or installer will advise on the frequency of cleaning. Failure to follow laid-down ventilation-system cleaning routines could render insurance invalid in the event of a kitchen fire.