Freezers: The big chill
July 25, 2016
by Joanie Spencer
Freezing is bringing together time and airflow through conduction, or heat movement within the product, and convection, or air movement around the product.
The science of baking is all about changing something from one state to another. In that respect, freezing can play a critical role in the baking process, in a variety of ways and for a variety of reasons. In essence, freezing stops time.
It can also speed up the process for many customers. Foodservice and in-store bakeries want quick solutions such as thaw-and-sell or par-baked products when time, labor and equipment are on limited supply. In some cases, freezing could even be used as a distribution strategy, as when a soft product like sliced bread needs to retain its shape and freshness during the shipping process.
Freezers work continuously in an extreme, often unforgiving, climate and with high production levels, and should something go wrong, it affects not only the process but also the people responsible for maintaining them. Regardless of the purpose — whether to halt a par-baked product or preserve the shelf life of a finished one — freezers must remain in tip-top working condition to do their jobs efficiently and keep the rest of the line moving as it should.
Balance is everything
In the spirit of efficiency, a baker should consider certain variables to achieve optimal freezing.
First, there is setting the right temperature for the product being frozen, and second is freezing in the right amount of time. Freezing too slowly will potentially dry out the product or too quickly at very low temperatures can kill the yeast, according to Peter White, president, IJ White Systems. The third variable, he suggested, is the system’s air flow design. “The proper control of the air moving through the product zone is essential for uniform freezing.” With hundreds of freezers in operation, IJ White has the experience and database to guide bakers in finding the right balance between these three critical factors.
Ashley Morris, sales manager, the Kaak Group, agreed that these critical factors require careful consideration in freezing. “It takes much time, as well as a very efficient air flow, to take that heat out of the center of products,” he said.
Of course, the harder a product is to freeze, the longer it will take. This is something Jon Hocker, director of technology and product line management, JBT Corp., explained as a matter of conduction (heat movement within the product) vs. convection (air movement around the product), thus, bringing time and air flow together (See “Know the frozen factors”).
Timing can also affect the economics of running a freezer, according to Mr. Hocker, and it, too, involves a balancing act. While slow freezing at a higher temperature may result in a lower monthly power cost, it also might require a larger equipment footprint. Faster freezing isn’t always better, and it’s all about that balance. “Timely freezing for JBT means that all factors are weighed and the freezing solution achieves the lowest all-in cost of freezing,” he said.
The freezing process essentially stops time.
The goal is always — aside from periodic maintenance — to keep freezers working in optimal condition at all times. But let’s face it: Sometimes, things break … and it’s usually at the worst time. Bakers must remember that freezer maintenance can be tricky, especially when considering the human factor. After all, to go in and fix a freezer, a maintenance employee may have to step into sub-zero conditions just to get the job done.
This is where planned preventive maintenance comes into play.
Mr. White emphasized the importance of heavy-duty component design with backups and redundancy of critical components. “If a motor or reducer goes down, you should not need to go to another part of the building to find a replacement and then have to change it out working in -30°F,” he said. “Today you should have redundancy built-in so the line can quickly go back into production.”
Linde also focuses on redundancy as well as easy access to components in its cryogenic freezer design for quick and easy maintenance. It not only makes maintenance easier on workers, but it also provides flexibility in that one point of mechanical failure won’t shut down the line entirely. “So if you experience a maintenance-related issue, you can rely on redundancy to run at some sub-optimum performance or capacity without the risk of completely shutting down a production line,” said Erik Fihlman, Linde’s marketing manager, baking and prepared foods segment.
He noted that the company’s freezers are designed to handle high production volumes and withstand extreme temperatures that can be very unforgiving on people and machines.
A good defrosting system will address snow build-up and maximize uptime.
Not a literal freezer temp, mind you, but metaphorically speaking, early diagnostics are critical to maintaining the health of a freezer and ensuring longer uptime.
At the Kaak Group, Mr. Morris suggested that monitoring critical components is key to effective maintenance during scheduled cleaning stops.
Linde designs its freezers for what it calls “trouble-free troubleshooting,” according to Mr. Fihlman. In other words, a maintenance worker should be able quickly identify and diagnose freezer components to know if they’re working properly. For components not visible to the workers, diagnostics are built into the HMIs. “They range from sensors and relays to outputs and not only identify specifically what’s wrong with a certain component but also where to look to troubleshoot to determine root causes,” he said.
Typically, a freezer runs six days a week with a day for inspection, maintenance and sanitation. But if a freezer must operate continuously for a longer period, JBT has internal sensors that report conditions and allow workers to better plan their maintenance schedules.
Snow development can also affect a freezer’s run time. Freezing equipment from the Kaak Group addresses defrosting for maximized uptime. “A good defrosting and cleaning program is essential to avoid too much ice buildup within the system during production,” Mr. Morris said. The Kaak Group’s defrost systems are equipped with their own fans or hot gas and can be used in combination with water.
JBT freezers feature a variable fin spacing coil. “Snow tends to accumulate on the coil face, eventually restricting air flow and resulting in reduced performance,” Mr. Hocker said. “The design of the variable fin spacing coil features wider fin spacing at the face and provides more surface area for snow accumulation before the air flow is restricted.”
Freezing equipment designed for “trouble-free troubleshooting” allows maintenance workers to see, feel or touch freezer components to know if they’re working properly.
Freezers frost over because low-temperature air can’t hold as much humidity as the warmer environment in the bakery. When the two collide, frost forms on interior surfaces. In such an extreme environment, sanitation is critical. “A freezer of any type will accumulate moisture from the product and the factory air due to the difference in temperature between the factory air and the freezer air,” Mr. Hocker explained. “The presence of moisture on the conveyor belt as frost, on any internal structures and on the evaporator coil makes the environment favorable for bacteria.”
To mitigate such risk, JBT’s Frigoscandia self-stacking freezer eliminates a significant amount of support structure as well as a drive drum surface, which makes sanitation easier, according to Mr. Hocker. “The design has less to inspect and less to clean,” he noted.
Because freezers are associated with sanitation concerns, it’s important to remember that they must contend with harsh chemicals on a regular basis. “All our freezers are designed with hygiene and cleanability in mind,” Mr. Fihlman said. “Hygiene is considered from a food safety standpoint and cleanabilty from a time and labor standpoint. In either respect, getting back into production with minimal downtime is very important,” he added, noting that Linde designs its CRYOLINE brand series of freezers in this way to efficiently go from sanitation back to production. “We consider access, harborage point elimination, sloping surfaces, cleaning mechanisms — all things that will reduce downtime.”
Sanitation should be considered from the human standpoint as well as design. “Everything is designed with the goal of eliminating any sort of contamination,” Mr. Fihlman said, “whether it’s standing water, food products or something external that might come in contact with the freezer from people.” Whether in the food process areas or the product zones, any part that a product touches or passes through should be considered for sanitary design.
Accessibility is another important factor. Workers must be able to see all parts of the freezer in order to clean it easily and effectively.
Whether cleaning, maintaining or just plain running product through the process, when operators take care of their freezer systems, the freezers take care of their products to stop time while continuing to move forward.