Chilling and freezing are two of the most common food preservation methods available to producers.  in fact, nearly all food production involves the addition of heat which then needs to be removed before further distribution.  Some products, like soup, are canned and heat sterilized, but must be cooled before leaving the factory.  Others, like cereal, are manufactured using heat, and must be cooled before packaging.  Chilled or frozen meat, poultry or seafood products are brought to their target temperatures during processing, and stored, transported, and displayed under those same chilled or frozen conditions.

Energy Efficiency

For some foods, the method of cooling or freezing has little impact on the final product, so the focus can be on energy efficiency.  Product attributes—such as piece size, moisture content, flowing movement, and packaging--require proper temperature control throughout the entire process line. Supplemental cooling helps maintain product temperature. When various cooling methods are employed in conjunction with conveyors and product movement, this creates a multi-method approach to cooling.  

For product exiting an oven, a cooling tunnel--either mechanical refrigeration or cryogenic—may be used depending upon space availability.  Even here, a multi-method approach makes sense.  When product exits the oven, each piece is steaming hot.   Adding ambient fan cooling can help dissipate much of the steam before it becomes trapped in the tunnel. This also takes advantage of the temperature differential between the cooked product and the processing room. In this instance, it is more efficient to use the large temperature difference available between the room and the cooked product prior to continuing to a freezing or cooling equipment.

Other multi-method strategies can also improve energy efficiency.  For example, if multiple SKU’s are frozen on the same production line, some may be more heavily loaded on the belt leading to larger freezing equipment.  Rather than using this larger equipment for all products, a better option may be to use a smaller spiral freezer supplemented with a cryogenic tunnel.  The cryogenic tunnel can be used only when needed for heavier loads, leading to greater operational efficiency.

Product Quality

In other cases, how the cooling or freezing occurs can be important to the final product quality.  Freezing scallops too slowly causes cell damage and results in a mushy finished product.   The same is true for fruit and produce. Conversely, freezing some filled products too quickly can cause the surface or outside layer to crack.  

For raw, marinated chicken breasts designed for retail, appearance matters.  A smooth, flat side can be achieved using a cryogenic plate-belt or super-contact freezer.   And while these freezers are perfect for freezing/setting one side of the chicken breast, it is not economical to exclusively use these freezers for the full freeze.  Once the bottom is set, another style of freezer should be used to complete the process.  In this case, a multi-method approach to freezing is advised.  In addition to a uniform appearance, the freezers mentioned improve yield by preventing adhesion and embrittling of small pieces of food that break free and are lost to waste.

Other multi-methods are available for creating proper chilling or freezing in pursuit of product quality.  A very quick cryogenic freeze immediately prior to a mechanical or cryogenic spiral freezer can be employed to secure moisture in a cooked product to minimize dehydration losses.  A cryogenic flighted belt freezer can be used for  individually quick frozen (IQF) products such as shrimp, vegetables or meatballs.

Source: Linde

Cost Control

In food manufacturing, production lines can quickly outgrow their freezing capacity as the demand  increases or formulation changes require more refrigeration capacity.  Large, new spiral freezers are expensive, and can require months of downtime for installation.  A quick and easy fix is to move to a multi-method freeze.  Adding a cryogenic system prior to a spiral freezer can greatly boost capacity along with yield savings.  Delivery and installation times are typically orders of magnitude lower than purchasing a new spiral freezer.  

Batch chilling or freezing of smoked or cooked products presents another challenge: the initial heat upon loading takes quite a while to dissipate even with blast chilling available.  A multi-method application using a cryogenic coil to return the batch chiller to its optimal operating temperature maintains the desired production values, and potentially allows an additional batch to be chilled per day.  

Operational

Some products are more easily manufactured using a multi-method freezing system.  Frozen, par-fried, sauced chicken wings are in high demand, but sauce pick-up is difficult on a par-fried wing.  The sauce warms up and drips off prior to freezing. A better approach is to use a spiral freezer to fully freeze the par-fried wings BEFORE applying sauce and use a cryogenic freezer AFTER applying the sauce to secure it.  There are several benefits to this approach.  First, the cost of using the cryogenic freezer is isolated to only freezing the sauce if the cryogenic freezer is after the spiral. Second, clean-up can be isolated to the sauce applicator and the cryogenic freezer when changing flavors.  By pushing the sauce application downstream of the spiral freezer, no sauce enters the spiral.  Third, pick-up of sauce can be increased dramatically.  Applying sauce to a frozen wing product is much easier than applying sauce to a hot or warm wing.  

In Conclusion

As shown in the above examples, removing heat from food products can—and often should—involve multiple methods. Whether using the processes described earlier, water cooling for canned goods, ambient cooling for baked products, or refrigeration for dairy, a multi-method approach allows processors to optimize production for energy use, product quality, cost control and operational efficiency.