Air filtration is an important but often overlooked or misunderstood part of food safety. It pays to hire an expert when designing or upgrading such a system, as it can get complicated and expensive. The most sensitive areas in a plant are between the oven and packaging where finished product is vulnerable.

Baked products exiting the oven are sterile. Recontamination occurs when product is exposed to contaminated air or food contact surfaces. Dust in the air inevitably contains mold spores. If your products are molding too fast, consider air filtration as a solution.

First, measure the amount of air being exhausted from the building. Regulations require that a certain amount of air be exhausted from gas-fired ovens to ensure that combustible gases do not accumulate. Also, during baking, all ovens generate significant amounts of moisture that can increase air humidity or cause condensation on cold surfaces like overheads and walls, resulting in dripping water or mold growth. Often new equipment is added to a facility without consideration of the additional air exhaust or moisture it will bring.

Knowing how much air is leaving the building, you can design an air makeup system to replace what is being exhausted and control humidity as needed. Maintaining positive pressure inside the building prevents unfiltered air from entering. Outside air must be filtered to remove the burden of dust, pollen and mold spores, which varies depending on the weather, climate and neighborhood activity such as construction or street sweeping.

Air handling units pass outside air through a series of filters: a coarse screen with a ¼-inch opening to exclude birds, leaves and large insects; a layer of non-woven fabric with a tackifying resin to capture and hold heavy dust; a low-grade paper filter to remove coarse dust; and finally, a fine, high-efficiency filter. The bird screen should be cleaned with a brush as needed. Visually inspect the low- and high-grade filters and replace when dirty. Don’t try to wash or vacuum them. Even better, install a vacuum gauge to measure the pressure drop across the filter and replace when it doubles. The filtration system should be capable of removing at least 90% of particles larger than 5 microns and 99% of particles larger than 10 microns.

Don’t forget that compressors push air into the building as well and must also be filtered, both incoming and at the point of use, wherever compressed air directly contacts finished product. Use a filter capable of removing 98% of particles larger than 0.5 microns.

As bakers address air filtration, there are several important factors to consider. Air exhaust rate, positive building pressure, outside air temperature and the desired temperature inside the facility, and the amount of moisture generated by the baking process will all impact the air filtration system. And when designing it, bakers cannot overlook filter replacement frequency and filtration of compressed air as that can also be a risk point for contamination.

Len Heflich is a contributing editor for Baking & Snack and the president of Innovation for Success. Connect with Mr. Heflich at heflichfoodsafety@gmail.com.