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Frozen storage

As Energy Costs continue to increase, improved operation efficiencies become more important. Some companies are using higher refrigerated warehouse storage temperatures for frozen foods as a way to reduce costs.

That was the subject of a Scientists Speak session held during the recent IARW (International Association of Refrigerated Warehouses)-WFLO (World Food Logistics Organization)-IRTA (International Transportation Association) Annual Convention. Conducted by Dennis Heldman of food science consultancy Heldman Associates, the session considered the tradeoff between reduced cost of operations and the losses of product quality associated with the use of higher product storage temperatures.

Heldman presented an analysis based on frozen food storage data, and on typical frozen food warehouse operations. For his purposes, he defined shelf-life as the time after entering storage that the product maintains acceptable quality when maintained at 0° F.

It is important to recognize, he stressed, that a product is changing continuously during storage, and the quality attributes are declining throughout the period of storage. In addition, any elevation of the product temperature above the reference temperature 0° F will increase the rate of product quality loss and decrease the potential shelf-life.

The savings in energy associated with maintaining the storage facility at a slightly higher temperature is due primarily to a reduced temperature difference between the outside environment and the refrigerated space, he explained. Any reduction in this temperature difference will reduce the thermal energy movement into the refrigerated space and decrease the corresponding load on the refrigeration system.

Heldman looked at three groups of frozen food: frozen vegetables — low dependence on storage temperature; frozen meats and seafood — moderate dependence on storage temperature; and frozen fruits — high dependence on storage temperature. His analysis was based on a 365-day shelf-life at 0° F, and the impact of adjusting the storage temperature from 0° F to 5° F, with an external environment temperature of 70° F.

The results of the shelf-life study, expressed as shelf-life and as a percent reduction as compared to the standard of 365 days 0° F, were:

“The impact of the adjustment in storage temperature is significant,” Heldman reported. “Although the reductions in product quality may not be evident when frozen foods move through distribution systems in time periods less than the potential shelf-life of the product, the sensitivity of product quality to temperature still must be considered.”

Increasing the product storage temperature from 0° F to 5° F indicates that the cost of energy could be reduced by approximately 7.5 percent, he said. The magnitude of energy savings would also be influenced local costs of electrical energy.

The opportunities for cost savings through elevation of refrigerated warehouse temperature for frozen foods are tempting, he noted, but they must be evaluated in contrast to the potential losses in product quality.

The dependence of frozen food shelf-life on storage temperature varies with the type of product, as some products are more sensitive than others.

The magnitude of the savings in energy cost, concluded Heldman, will depend on external environment temperature and local electric energy cost, as well as other operating conditions at the warehouse.

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