How to protect the containers from spoilage during Retort processing

It is very important to study the behaviour of flexible containers during the retort processing to make sure that the containers are not exposed to high stress and stretching during the processing. Over stretching of the flexible containers lead to the loss of barrier properties and in turn fail to achieve the shelf life.


During Retort processing, during the come up period of the heat process cycle, the pack headspace heats rapidly, relative to the pack contents, and consequently the overpressure should be increased to its specified maximum as the vessel temperature increases.


At heat processing temp, the overpressure should be controlled within +/- 1 psi.


During the cooling period, the headspace will cool and contract rapidly, and again the overpressure can be reduced with vessel temperature


The overpressure required to prevent excessive expansion of pouches during retorting will depend upon the amount of gas in the pack and the heating temperature.


The development of pressure within the packages when heated is caused by :


  • Expansion of headspace gases
  • Expansion and release of gases entrapped within the food product
  • Generation of water vapour
  • Release of gases due to reduced solubility of dissolved gases at higher temperatures.
  • Thermal expansion of the solid and liquid phases of the food.


The following defects could occur to the pouches due to inadequate over pressure controls :-


  • Delamination
  • Loss of Barrier Properties
  • Over Stretching
  • Weak Seal
  • Bursting
  • Waffling
  • Channel Leaker
  • CUT or Puncture
  • Flex Cracks
  • Leaking from the surface


How to Solve this problem ?


To establish the correct overpressure, the flexible containers can be either processed in a retort with a window or with Ellab Deflection Measurement Device.


Using this device, it can be detected when the pouch is starting to expand excessively. The pressure being applied to the pack can then be increased until the expansion is under control.


The resulting pressure profile must be recorded and this record can then be used as the basis for an automated pressure control profile in production.


The Ellab system offers probes to measure the pressure inside the retort chamber, the pressure inside the pouches and the deflection / deformation / stretching occurring on the pouches during retort processing apart from the Fo values and Cook values obtained to the products during retort processing.


These data help the processor to define the required over pressure to be applied to each type of products and can in turn save the flexible containers from spoilage. This will help the processor to achieve the target shelf life to the products.