Value-added protein foods are fertile ground for flash-freezing, and DiMaggio cites the emergence of convenience stores as sellers of sandwiches and fast meals as a prime opportunity. "Small chains have grown significantly in quick service foods," he observes. "The cryogenic option offers them an inexpensive way to increase throughput," and he believes increased throughput is the primary reason for using the technology.
Building better boxes
DiMaggio pegs the cost of cryogenic freezing at 3-4 cents per pound, and the cost of maintaining food in a frozen state throughout the supply chain adds more cost. Optimized freezing technology is therefore central to both controlling costs and maintaining margins.
One way to increase throughput and improve product quality simply is to freeze at a lower temperature. More fans and higher-velocity air helps, but dialing down the thermostat has the biggest impact. "At -20 degrees Fahrenheit, CO2 is about the same efficiency as ammonia," notes Luke Facemyer, director of design for refrigeration at Jacksonville, Fla.-based AEC firm Stellar. "At -30 degrees or -40 degrees, CO2 is more efficient on the low side" of a cascade system that combines an ammonia loop and a carbon dioxide loop as refrigerants.
Until a decade ago, cascade systems were concentrated in Europe. Then, in 2003, a European food company commissioned what was believed to be the world's largest application in Jonesboro, Ark., where Nestle opened a 525,000 sq. ft. Stouffer's and Lean Cuisine facility. Stellar was the AEC firm on the project. Since then, the company has designed a dozen more, Facemyer estimates. Keeping ammonia out of processing and warehouse areas is part of cascade's appeal, but when the temperature set-point is dialed down to -30 degrees, CO2 can lower energy costs 10-15 percent.
The physics of freezing are not subject to change, but today's freezers are more efficient than those of the not-too-distant past. "Before, it was just an evaporator in a box," Facemyer scoffs. Now, the velocity and direction of air flow is tightly controlled to achieve a better heat-transfer coefficient, and VFDs on fans throttle back power consumption.
Value-added protein products are lifting many food companies out of the commodities game. Poultry products that are glazed, marinated or otherwise further-processed are among the stars of grocers' freezer aisles. Releasing those products from a steel or wire-mesh belt is a challenge, however, and some companies have turned to plastic belting.
Plastic brings its own baggage to freezing. A plastic belt lacks the structural integrity of steel, and sagging under heavy loads is a problem that may require additional belt rails. Airflow is another issue: Modular belts are denser than their metal counterparts, which means air flow through the belt is constricted, resulting in longer dwell times.
Ashworth Brothers Inc.'s answer was to split the difference with a hybrid design that combines stainless-steel support rods and acetal modules. According to John Lasecai, chief engineer at Ashworth, Winchester, Va., independent testing has quantified significantly reduced air pressure drop across Advantage hybrid belts compared to all-plastic modular belts, resulting in faster freezing and higher throughput.
"Plastic is important for product release and also for sanitation because of loose meat that might get caught or poultry with a sugary glaze, which can act as a binding agent," Lasecai says. A cautionary note with plastic is the abrasions and scratches that can provide harborage for bacteria. "We don't recommend plastic for all applications," he allows, and the bulk of the firm's belting sales are still metal, but for freezer conveyance, hard plastic modules offer advantages.
To revive frozen sales, product packaging also could stand a makeover, particularly in terms of plastic films that are greener. Retailers are pressuring suppliers to use recycled content, both for products in freezer cases and those shipped frozen and sold as fresh, maintains Roman Forowycz, chief marketing officer at Clear Lam Packaging Inc. in suburban Chicago.
The functional performance of rollstock "made from old soda bottles" has derailed many migrations to more contemporary packaging, however, causing manufacturers to move slowly. Tyson Foods is introducing an all-polyethylene pouch that does away with adhesives for easier recycling, but it's taking the frozen-chicken product on the road to Mexico before introducing it stateside.