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MIXED STORAGE Joshua , with regards to units that are used for mixed storage we find that in small installations , separate facilities for each and every product are economically not justified , hence , a number of products are usually stored together . Storage conditions will then be a compromise , temperatures usually being above the optimum for some products to prevent damage to the more sensitive products stored in the same cold room . Sealing products in plastic or glass prevents evaporation and thus serves to maintain the quality of certain products .
Higher storage temperatures tend to shorten the storagelife of some of the products held in the mixed storage . When products are stored for short periods , however , this is not normally a serious problem . In larger installations , products are grouped for storage and only those requiring similar storage conditions are placed together .
Products which give off odour should never be stored with other products . Dairy products are highly sensitive to this .
PREPARATION Joshua , some consideration to the preparation of the food stuffs prior to storage is advisable .
One of the most important factors that determine the maximum storage time of a product stored under refrigeration is the condition under which it enters the cold room .
Refrigeration only stops or slows down the natural process of deterioration and cannot restore an already deteriorated product to its original condition . Nor can refrigeration improve the quality of a product . For these reasons , only undamaged products of high quality are suitable for storage . Since deterioration of food products starts immediately after harvesting or slaughtering , it is important that products are cooled to the storage temperature as soon as possible . Products that need to be transported over long distances should be precooled and shipped in refrigerated transport .
Joshua , other aspects of preparation include , chilling , blanching and the ageing of meat .
Product chilling refers to the rapid cooling of a product from harvesting or slaughtering temperature to the storage temperature . Rapid chilling and high air velocities are desirable during this time so that the temperature and vapour pressure of the product are lowered as quickly as possible to avoid excessive moisture loss and shrinkage . High air velocities carry away evaporated moisture and prevent the recondensation of moisture on the surface of the product . High velocities also greatly increase the heat transfer rate . The humidity should be high when chilling to prevent excessive moisture loss .
Blanching is accomplished by immersing the product in boiling water or steam for a short period , the length of which depends on the nature of the vegetable . It ranges from one minute for hulled peas to 10 minutes for corn on the cob .
Both vegetables and fruit must be cleaned and washed to remove dirt , insects , juices and any other foreign matters before chilling or freezing . Vegetables are then blanched . Most micro-organisms are destroyed by this process . However , some bacteria may survive and to prevent spoilage by these bacteria , the product should be chilled in cold water ( about 10 ° C ) immediately after blanching and then dried thoroughly before packing . Blanching of fruit is not practiced . To do so would destroy its fresh quality , a characteristic that is highly valued .
Joshua , as a general rule , meat products do not require special processing prior to freezing . Pork and fish must be frozen immediately after chilling . This is because of the instability of the fatty tissues . Beef is often allowed to hang in a chiller room for a couple of days before freezing . During the ‘ hanging ’ period , the beef is tenderised by enzymic activity .
Beef carcasses must not be aged or ‘ hung ’ for excessive periods as this will affect their storage life . Poultry must be aged for 12 – 24 hours before freezing . Ageing makes its meat more tender than if it were frozen immediately after slaughtering .
FROZEN STORAGE The exact temperature for frozen storage is not critical , provided it is low enough and does not fluctuate . About -18 ° C for short term and -21 ° C for long term is recommended . The temperature should remain as constant as possible during the whole period of storage . Some products are particularly sensitive to temperature changes . The accuracy of automatic equipment is generally in the range of 1 to 1.5 ° C , which is acceptable .
As many packaging materials do not offer complete protection against dehydration , the relative humidity should be kept at 85 to 90 % in frozen storage rooms . This is particularly important for long-term storage .
Proper stacking of products is also important . Adequate air circulation must be maintained around the product . Space must also be left between the stored product and the walls of the storage room in order to eliminate the possibility of the product gaining heat directly from the walls .
Joshua , I hope that this increases your understanding of the basic aspects of food storage . As you can see it is not just the temperature that is important .
Thanks to everybody for the overwhelming response . I receive an average of over 60 questions a month and cannot answer all of them . But keep them coming , as I may answer you directly . Looking forward to hearing from you . RACA
Grant Laidlaw
REFERENCES 1 . SETA training 2 . ASHRAE 3 . ACRA
www . refrigerationandaircon . co . za RACA Journal I April 2024 39