The frozen foods category has evolved over the past decade, and along with it freezing technology. Food processors are seeking technology to help them achieve more throughput, higher efficiency and certainly flexibility to meet changing market dynamics.
"Some manufacturers are capitalizing on consumers' increasing preference for in-home cooking rather than eating out," says Corey Henry, vice president and spokesman for the American Frozen Food Institute, McLean, Va. "So 'restaurant-inspired' gourmet meals that carry a higher price tag are appearing on grocers' shelves – and are finding favor with consumers that perceive them to be a good value relative to restaurant foods."
To stay relevant as the marketplace – and technology – changes, processors have been demanding greater throughput, longer runtimes and in greater overall efficiency. Faster lines with wider belts, better defrost strategies, refined conveying and perhaps an increased role for hybrid mechanical-cryogenic systems all share the spotlight in this effort.
Spirals still the mainstay
A diverse industry demands a multitude of freezer designs that include fluidized bed IQF freezers, impingement freezers, specialized flat-patty freezers, film/plate crust freezers and various cryogenic alternatives. The spiral freezer, and in particular the self-stacking spiral, has become a mainstay of many high-volume plants, squeezing ever-more product through ever more compact designs.
The latest from JBT FoodTech Sandusky, Ohio, accommodates 45 tiers in a unit that measures 36 ft. x 15 ft. with an 18-ft. height. "That particular freezer will handle 8,000-10,000 lbs. an hour of par-fried chicken nuggets at minus-40 [F], and if you run even colder, it'll do more," says Andrew Knowles, JBT freezer sales support manager.
He says it's "an incredible capacity for such a small footprint," and he's got a point, considering the new model can achieve 40 percent higher capacity over a prior model still fast and still popular with processors.
Wider conveyors are a big part of the push for more throughput. That new, compact JBT spiral, for example, provides usable belt width of 40 in., whereas 28-36 in. surfaces earlier were the norm. It's not that plants are running 40-in.-wide super-chicken breasts; it's about throughput and plants wanting to remain agile in the face of change. "They don't want a freezer that can only handle chicken nuggets, they want a freezer that can handle a variety of products," Knowles says.
Of course, you can't simply widen the belt alone, because that would require slowing-down the line and adjusting freezing times, which in turn can change other factors including the product itself.
"To be effective, the spiral freezer needs sized correctly to achieve the proper dwell to reach target core temperatures," says Jonathan Lasecki, chief engineer for belt-maker Ashworth Bros, Winchester, Va. "This requires spiral freezer belts to be wider, operate faster and be capable of the increased product loading."
Sequential defrost is a relatively ubiquitous offering across freezer types, and is especially useful when hot, steamy products generate a lot of ice and "snow" buildup. By isolating and defrosting each coil bank individually, "a plant can run for multiple days without stopping," says Knowles, a boon to plants, especially "fully cooked plants that can now run continuously, where traditionally they would have to stop the line to clean and defrost every night."
He adds that where plant space won't allow redundant fans and coils, air defrosting "is a very low-cost and effective way to achieve long run times, and it doesn't require extra fans and coils, so you can keep your footprint very small." This solution uses a manifold-type system that bursts air to knock the snow off the coils.
Cryo-mechanical crust freezing
Cryogenic freezing has proven itself a highly capable technology, although the availability and cost volatility of CO2 and nitrogen can limit applicability. Some believe it's not cost-efficient for lines producing more than 1,000 lbs./hr.
"If your product costs 40 cents a pound, and it costs 10 cents a pound to freeze cryogenically versus 2 or 3 cents a pound to freeze mechanically, there's just not enough margin to go with cryogenic freezing," says Ron Idol, food business development manger with Air Liquide USA, Houston.
On the other hand, he maintains his cryogenic systems can be highly cost-efficient when applied to products with high moisture content -- due to the loss of all that moisture, and therefore weight, that results from mechanical freezing.
This drives many processors of many products, from frozen novelties to meats, to add a crust-freezing step before entering, for example, a spiral for deeper freezing.
Additionally, the technique reduces sticking problems that can degrade quality and throughput.
"Crust freezing is very important and is going to become even more important," Idol says. While this can be done using conventional as well as cryogenic systems, he says cryogenic systems reduce weight loss or dehydration to as low one-quarter percent and seldom above one-half percent, compared to the "newest and best mechanical systems, which are getting around 2 percent weight loss," he claims, or older systems that give-up even more.
"Where crust freezing comes in is if you can quickly seal the surface by freezing cryogenically, and then go into a mechanical system, the product will not continue to lose moisture," he says.
Product preservation justifies the cost, Idol says. Using the example of a line producing 25,000 lbs. of fish filets a day, valued at $2.40/lb. – and assuming an existing spiral produces a moisture-weight loss of 2 percent – he calculates that a processor can save more than $130,000 a year using nitrogen crust freezing.
Cryogenics sometimes warrant installation for other applications that go beyond per-pound calculations. Some plants lack the space to expand their process or engine rooms. Others may lack the financing for an expensive capital improvement but have ready cash-flow to keep supplied in cryo gas.
In such cases, a cryogenic system can achieve comparable throughput to a mechanical system in one-fourth the plant space, Idol says, at a lower up-front cost and with lead times as low as a couple of months. "So very quickly and inexpensively you can get your product to market with cryogenics when it's physically or financially impossible to do it any other way."
Conveyor surfaces evolve
Inside the freezer as well as out, advanced plastic materials engineering is helping expand frozen food conveyors' ability to:
- Handle high temperatures.
- Keep products correctly oriented.
- Keep products from touching and freezing together.
- Hold the product on steep inclines to the top of a spiral freezer.
- Whip products around curves at higher speeds.
Integral lane dividers woven into the mesh address the problem of products shifting, twisting and jamming as it shuffles down the spiral belt. Similarly, higher-friction areas can be built into belting to keep, for instance, long Italian breads, oriented the "long way on the belt," says Ashworth's Lasecki. He says these solutions solve problems over older belts that were so hobbled in functionality that "you'd only be able to use the outside half of the belt."
Advanced acetyl, polymer and other materials address tolerances such as wear and temperature where conventional plastics would warp and curl on the frozen line. "One moment, a section of conveyor is covered in ice and the next, you're coming at it with 140-degree water for sanitation," says Mike Hosch, director of product development for Dorner Mfg. Corp., Hartland, Wisc.
A curved section of conveyor with a top speed of 100 to 150 fpm can today run at 250 fpm due to the use of alternative materials and belt styles, according to Hosch. But not without some attention to potential problems. "A straight-running conveyor will be fairly consistent in its wear points, but a curve conveyor running quickly will have hot spots and high-wear points," he says. "We often use either a harder material in those areas or plastics with FDA [accepted] lubricants embedded in them."
