Preserving quality and safety
As consumers demand food and beverage products made with fresher ingredients, refrigeration and freezing technology becomes more important.
The clean label movement has been seeking and destroying artificial ingredients in food products for a number of years now. And, big companies, such as Kraft, Nestlé, General Mills and Campbell Soup, continue to remove artificial coloring and flavoring from their food products.
However, fresher and simpler foods require more effort to preserve their quality and safety. Cooling and freezing are two methods processors use to slow down the microbiological processes that can lead to food deterioration. However, the equipment design and heat transfer mechanisms can greatly affect the final outcome.
“The continuing evolution of refrigeration components, system architecture and equipment plus facility monitoring technology is helping food manufacturers, processors and related partners up and down the chain keep food fresher for longer periods of time,” says Andre Patenaude, director of CO2 business development, Emerson Climate Technologies.
To assist processors in meeting consumer demand for fresher, less processed foods, equipment suppliers are providing solutions with larger capacities and more hygienic designs that chill and freeze more quickly and efficiently. The better cooling and freezing technologies also can help reduce waste and conserve energy.
Efficient chilling and freezing
Microorganisms, such as bacteria, molds and viruses, can change the taste and appearance of foods like meats and fresh fruits and vegetables and eventually lead to spoilage. Cooling the temperature of these foods slows the growth of microorganisms and increases the foods’ shelf life by several days. For longer preservation, freezing is required. But, how well the quality is preserved is directly related to the rate of freezing. The quicker the freezing process, the smaller the ice crystals.
“Both time and energy efficiency are areas of focus for protein processors that need to chill or freeze their products,” notes Mike Lightfoot, chief executive officer, Milmeq. “Because of this, plate freezing is one of the technologies growing in popularity.”
“Plate freezing provides an alternative solution that can halve the freezing time, significantly decrease energy consumption, reduce manual handling and enhance product shelf life compared to air blast freezing,” Lightfoot says.
For a faster, more energy-efficient freeze, plates filled with refrigerant are positioned to make direct contact with cartons of product. The freezing cycle of these plate freezers is 24 hours, compared to the 48-hour freezing cycle of air blast freezers. The faster freeze improves the refrigeration index—a predictive model that calculates the potential growth of microorganisms—and increases output.
Technological innovations also help freeze food more efficiently by eliminating dead zones, areas where the cold air does not reach the product, explains Justin Lai, vice president of sales and marketing, Food Process Solutions (FPS). “Airflow modeling software can minimize or eliminate dead zones, ensuring air is directed uniformly through the product zone,” he adds.
FPS offers Continuous Flow (CF) freezers with MultiPass airflow technology. The line was developed in partnership with Freezing Solutions Ltd. Additionally, FPS manufactures the PulseFlow IQF tunnel freezer designed to distribute air uniformly across the conveyor belt and direct high-velocity air pulses to crust freeze and cool products more efficiently.
“Crust freezing seals the product surfaces, reducing dehydration and freezer burn,” says Lai. “A quick freeze also develops smaller, finer ice crystals that reduce ‘weepage’ during thawing.” Preventing weepage improves the quality and taste of frozen food since it keeps the cell structure of the food intact.
Crust freezing has also helped cookie dough producers with handling, slicing, stacking and packing of products. For example, with the Linde inline impingement cryogenic freezer, raw cookies receive an initial blast of liquid nitrogen as they enter the unit. This is followed by a controlled flow of nitrogen gas as the cookies are carried through the freezer on a conveyor belt. According to Mark DiMaggio, head of food and beverage for Linde, the freezer has three to five times the capacity of a conventional cryogenic or ammonia-based tunnel freezer.
Clearly, the faster the freeze or chilling time, the less energy is consumed. Low-condensing refrigeration systems also maximize energy efficiency by using electronic expansion valves to take advantage of lower ambient temperatures, says Emerson Climate Technology’s Patenaude.
Instead of operating at the same level regardless of the outdoor temperature, this technology varies or “floats” the condensing pressure in accordance with fluctuations in ambient temperatures. Years back, fixed head pressure operation using thermal expansion (TX) valves aimed to do this, but as capacity fluctuated, flash gas bubbles formed from the liquid refrigerant, which could cause system failure.
However, low-condensing systems use electronic expansion (EX) valves at the evaporator, which digest any flash gas that may be produced as the head pressure adjusts. As the outdoor temperature drops, the head pressure floats down with it, and the compressor capacity increases as the EX valves digest the flash gas.
“Keeping tighter control of temperature set points helps reduce fluctuations,” Patenaude says, “giving food processors and manufacturers the opportunity to reduce waste and authenticate freshness. It also enhances energy efficiency.”
The GEA Omni control panel enables the precise management of floating head pressure among multiple integrated compressors in food production. Maren Fiorelli of GEA corporate communications department says lowering the condensing pressure allows refrigeration systems to perform more efficiently, resulting in significant energy savings, reduced costs and fewer compressor failures.
“In the last couple of years, controls systems have been significantly improved and are more affordable,” says Evis Buli, sales engineer, Berg Chilling Systems. “The small investment in a good controller is easily justified by its return.”
Berg hybrid and free cooling chillers make maximum use of cold outdoor temperatures, decreasing energy consumption. With a good control system, operators can maintain better cooling temperature profiles.
“A good control system also leads to a smoother operation and less downtime due to equipment malfunction,” Buli says.
The growth of microorganisms must be prevented by controlling the environment food is kept in. “Simply put, the goal is to avoid temperature disruptions and keep food within a safe zone,” offers Patenaude.
New technology is helping processors have more control over refrigeration integrity. For instance, combined heat and power (CHP) systems can reduce the risk of power outages. Also, digital diagnostics can offer insights into major issues with the potential to cause equipment failures and unexpected downtime. “It’s all about making sure the right amount of refrigeration is being maintained at all times,” Patenaude adds.
For example, when Fletcher International Exports, an Australian processor and exporter of lamb and sheep products, recognized it needed to freeze its hot boned products at a faster rate, it opted for new plate freezers. “With a more efficient chilling or freezing system, the temperature of a perishable product, such as meat, is lowered more quickly, and bacteria growth is minimized,” states Lightfoot.
The hygienic design of chilling and freezing equipment also is a big factor in producing safer food. Since freezers and chillers are typically large pieces of equipment, the process of manually cleaning them thoroughly can be difficult.
“Any contamination in one spot can easily be spread to the rest of the equipment through the circulated air,” says FPS’s Lai. “Therefore, a simple, effective cleaning system is essential.”
FPS mounts motors and controls on the exterior of its equipment to ensure all interior surfaces are smooth, sanitary and easy to maintain. Also, to ensure the freezers are hygienically designed, FPS incorporates fully welded stainless steel enclosures and a clean-in-place system.
“In cold room applications where washdowns involve corrosive chemicals, the evaporators and unit coolers should have coated coils and stainless steel casing,” says Berg’s Buli. “If they don’t, the material will corrode, and the oxidized material will be blown into the process area.”
Processors using older types of refrigerants should be aware of the EPA’s Significant New Alternatives Policy (SNAP), which prohibits the use of certain chemicals that pose a high risk to the ozone layer and have a global warming potential (GWP), toxicity and other unfavorable qualities.
“At some time in the future, these facilities will need to consider moving to lower-GWP hydrocarbon or natural refrigerants based on the EPA’s SNAP program,” says Patenaude.
A cascade CO2 refrigeration system can help reduce energy consumption and chill food more efficiently. A cascade system has two (or more) refrigerant circuits, each with a compressor, condenser and evaporator; the evaporator of one circuit cools the condenser of another.
“CO2 is a very efficient refrigerant and has the lowest GWP,” says Buli. “It has successfully been used as a volatile brine in multiple facilities, eliminating the need for ammonia in process areas. The ammonia/Freon system is contained in the mechanical room, while the CO2 is pumped around the facility.”
This setup can significantly reduce the ammonia charge and confine ammonia to the machine room. Additionally, FPS’s Lai says the implementation of these systems enables operating at lower suction temperatures, allowing smaller freezers to be used.
On the other hand, Milmeq single station opening (SSO) plate freezers allow only one set of plates to open at time for loading or unloading product and deliver up to three and a half additional hours of freezing time. “The plate evaporating temperature can be raised to further reduce energy consumption,” explains Lightfoot.
For blast freezing and cooling, many design elements of a processing facility itself should be considered. “For example, the room layout is very important,” says Buli. “It needs to be designed for maximum airflow.”