When dairy processors consider how the air in their facilities impacts the safety of the products they are making, they have much more to ponder than just filters and flow.

In terms of basic principles, a facility always needs its airflow to travel from its high hygiene areas to its lower hygiene areas, said Tim Stubbs, the Innovation Center for US Dairy’s senior vice president of product research and food safety. Transitions are a second significant factor, Stubbs said.

“The ingredients have got to get into the room or the packaging materials have to get in the room,” he said. “So how do you manage those transitions? How do you manage the airflow in that transition, and the human flow and the material flow and all that?”

More questions and details to contemplate exist around every corner, or through every door. As Stubbs pointed out, just opening a door to travel from one room in a facility to the next changes the pressure differential between the two areas.

As an example of an even more sophisticated situation, Stubbs rattled off concerns that may accompany a high hygiene area, where air pressure is the highest.

“What happens when I turn on and off my dryer, which is a giant air mover? Have I accounted for that? What happens if there’s a power interruption? There is actually a lot of thought and a lot of design that goes into, which way does the air flow? How do I maintain that? How big can a door be? How long can that rolling door stay open and in what manner does it open and close? And do I have controls in place to make sure I don’t have 12 of them open at once?”

As Stubbs explained, the design is “really simple” in terms of a high-to-low flow, but “it’s really, really complex in execution.”


Complex transitions

Jeremy Travis, vice president of quality and technical services for Hilmar Cheese Company, Inc., said the sequencing is not always obvious. Along with the air moving from highest care to lowest care areas, Travis said air in dairy processing facilities must flow from dry rooms to wet rooms, as well, because if that doesn’t happen, “you’re guaranteed going to be contaminating products somehow.”

What’s more, he said improper air flow could have detrimental effects outside of the food safety realm.

“You’re just attacking the shelf life of the product,” Travis said of a misstep leading to air contaminating a product. “You’ve created a shelf-life condition.”

Lindsey O’Brien, president of the Wisconsin Association for Food Protection, said monitoring air quality is a must for processors.

“I think it helps to think of air as a product contact surface – anything carried in the air can come into contact with your product,” O’Brien said.

Frequent testing and risk assessments also are paramount, she said, while taking into consideration not just air currents, but also foot traffic patterns, duct vents and the opening and closing of doors.


Building the right environment

Even before an air system is put in place, Travis said a company needs a building that is “buttoned up,” with all the necessary controls in place.

“The reality is you could put the best air system on the best building, but if for some reason you have a condition where two doors could ever be open at the same time,” that would lead to issues.

For ready-to-eat products, if a facility has a door to the outside from a processing area, Travis said a transition room should be in place. At the Hilmar facility across the street from his office in Hilmar, Calif., he said every roll-up door has an adjacent transition room.

“But those two doors can never be open at the same time, allowing for the loss of positive pressure or a draft into the building,” he said.

Hilmar created a single point of entry and exit for all personnel at the facility and put transition rooms on every door from the plant to the outside. Travis said that created a “nice envelope over the building,” that allows the air system to reach its full potential.

“It might be mission critical for dairy, but these are becoming the standards,” he said. “Anyone who’s building a food plant is building a building that envelops the process and protects product and the air systems.”

Even the location of a facility can have an effect on the air quality.

“Dairy processors tend to be in highly agricultural areas,” Travis explained. “You’re usually not trucking all the milk into some highly concreted, perfect climate. You’re usually in animal agriculture environments, remote from cities, which means dirt’s being turned, wind is probably present. So you have a big external factor.”

These are the types of lessons food safety experts in the industry have learned through experience over the years.

“You can’t just build a building,” Travis said. “You have to build a building that protects under that condition as opposed to build a good building and then throw some air on it.”

He added: “If your environment is very windy and has a high turn up of dirt, the particles that move in the wind are going to be really small. So if you don’t pre-filter before the tip of the unit’s filters, you’re going to choke them out and lose airflow. You have to just understand what you’re filtering.”


Avoiding contamination

Justin P. Miller-Schulze, PhD, is an associate professor in the department of chemistry at Sacramento State University, where his expertise lies in the realm of chemical analysis for trace level contaminants in the air. He said from a quality assurance and quality control perspective, the use of high efficiency filtration systems to control air quality helps prevent both outside-to-inside and cross-contamination of dairy products.

Processors should keep in mind that air quality can impact their products, Miller-Schulze explained.

“Bacteria and fungi can represent a sizable fraction of particulate matter depending on the source, and a dairy processing facility could reasonably be expected to generate particulate matter that would have both bacterial and fungal components,” he said.

Stubbs said much of the food safety work being done at a facility involves avoiding post-pasteurization contamination.

While companies do all they can with procedures and plans to keep hygienic zones hygienic and make sure nothing is coming in contact with the product in the pipe, Stubbs said at some point in time air is going to get in there somehow.

“So even filtering the air to get it in there as the pneumatic blower for the hygienic in the pipe is critical,” he said.

Because air is a carrier, Stubbs explained, proper air quality is “super critical,” and that goes not only for filtering out dust and dirt, but also monitoring temperature and humidity.

“If I have really moist air, and it’s warm, and I suddenly cool it down, I’ve got condensate,” he provided as an example. “And now I have water and I have water somewhere I don’t want. And I could have growth somewhere that I don’t want. So there’s just a lot of aspects of it.”

Such details must not be overlooked, O’Brien said.

“Bacteriophage movement in a cultured dairy products plant can be greatly affected by airflow and air filtration,” she said. “Managing air quality to minimize phage spread can help keep your culture program more manageable.”

Miller-Schulze estimated that the concern for the introduction of “wild-type” bacteria or fungus would be elevated at facilities dealing with cultured dairy products.

Within the industry, Stubbs said he has found that companies, particularly “the big players,” are “very thoughtful” about all of these factors. He said companies want to make sure the air is impeccable when it is in a bagging room.

It’s important to properly manage air quality in facilities, Travis said, because dairy processors make ready-to-eat foods that are handled in highly specified details along the path from raw to final product.

“The air quality is a very critical ingredient, because at the end of the day, just before the cheese is bagged, the powder is bagged, it’s exposed to air usually,” he said. “There’s going to be some gap.”

Whether dairy processors are dealing with fluid milk, ice cream or fermented products such as cheese, whey, cottage cheese or yogurt, Travis said they are going from milk to product in a matter of hours. That’s why different environments are necessary for different stages – whether that be raw, processing or ready-to-eat. And for companies that produce ice cream, for example, they need an ingredient environment, too. Cheese processors typically need a wet environment and a dry environment.

“You have to figure out what is your highest to lowest care, so you get the right flow of air,” Travis said.

To help dairy processors find solutions to such puzzles, Stubbs said the Innovation Center for US Dairy identifies experts to teach classes and create educational content for the industry. Processors can access guidance documents, attend workshops or webinars, or send employees to receive training from top professionals.