The process of freezing products for the food and pharmaceutical industries has evolved tremendously over the past 50 years. Ranging from standard blast freezing to the newer cryogenic freezing systems, the technology of plate freezing has been overlooked for the last 20 years but is still a viable and cost-effective way to freeze products in high volumes.
Plate-freezing technology evolves from its simplest form of two metal plates filled with refrigerant that are in contact with the product packaging. The traditional refrigerant used in this application is anhydrous ammonia, but plates have been designed to use refrigerants ranging from fluorocarbons to carbon dioxide. The refrigerant used is based mainly on a mix of customer preference and practical application.
The plate freezer can be considered a true portable system. Instead of having a dedicated freezer or refrigeration section, the user can place the plate freezer anywhere in the production line as long as the necessary utilities can be provided. Some equipment manufacturers even make small self-contained units that can be used in either a product development laboratory or in small specialty food companies. This allows for the development of packaging and formulation that can take advantage of the freezing technology used in production facilities.
The advantages of this technology are shorter freezing times and the ability to completely package the product in an inert atmosphere before freezing, which minimizes both product oxidation and post-freezing processes. The pressure from the plate being in contact with the package also keeps the package product uniform for easy post-packaging into shipping cartons. An example of this is raw-fish packaging in the Nordic countries. The processors use forms and plate freezers to produce uniform packaged blocks of fish products.
As with all processes, there also are disadvantages. Plate-freezing technology requires the packaging of product to be generally uniform, and the product should be in contact with two sides of the packaging that will be in contact with the freezing plate. This is not a necessity, but to gain the highest productivity, it is desired. It also is considered a semi-batch process, which involves loading each plate with a uniform amount of product and then lowering the upper plate to make contact with the product packaging. Currently, this is done by automation packages, supplied by every manufacturer, that consist of automated plate-loading and plate-handling mechanisms. Equipment manufacturers also include the ability to integrate the plate freezer into the supervisory control system to allow complete remote monitoring and control.
Periodic DefrostingMaintenance is paramount with plate freezers. Periodic defrosting is mandatory to minimize ice buildup on the plate surfaces as well as the handling mechanisms. The time before defrosting is dependent on mainly atmospheric conditions. Because a plate freezer can be installed anywhere in a production line, the humidity within the building is a major factor in determining the defrosting periods required to maintain the freezer's operational capability.
Mechanical maintenance requirements are simple and can be accomplished easily by personnel in the plant. Most makers of plate freezers use simple hydraulic and mechanical mechanisms to move the plates and the product through theunits, so a user's understanding of hydraulic controls and knowledge of the refrigeration system are required. The information is no different from that of maintenance systems existing in every major processing plant in the world.
The area that requires the most maintenance is that of the product-loading mechanism, which is the key to providing efficient mechanical operation of the plate freezer. Basically, the mechanism is a "push bar" that activates when the product is positioned on a conveyor in front of the freezer opening, and then pushes the product onto the plate. This continues until the plate is full of product and is cycled out of position. Wear and poor adjustments on this loading mechanism can cause problems. When the push bar is out of alignment or the conveyor is not lining up the product correctly, the mechanism will jam the machine and stop the production line.
Minimal LimitationsThe limitations that are associated with plate freezing are minimal when compared to the advantages such as faster product freezing, less dehydration and lower energy use.
The main point of using less energy is that instead of chilling down air to the required freezing temperature and then moving it inside an enclosure, the system actually is cooling a metal plate that is in direct contact with the packaging of the product. Plate freezing can be up to 40 percent more efficient to operate compared to other freezing technologies.
The capital costs of using plate-freezing units typically are much lower than that of blast-freezing equipment and there is more flexibility in the operation. Taking into account all the information and products available for freezing, plate freezers are a viable technology that can provide substantial savings and flexibility to any freezing application. PCE