Validation or Regular Monitoring ? Which is better for Retort Processing ?

Validation includes Heat Distribution and Heat Penetration Studies.


Heat Distribution Tests are designed to ensure that the sterilizer is at a uniform temperature inside the process chamber throughout the process. The Temperature Distribution Tests should be designed to locate the slowest heating area in the sterilizer. Once the slowest heating areas are located, the test probes should be concentrated in that area of the sterilizer to determine the parameters required to bring that area of the retort to a uniform temperature


If more than one container size or type is processed in the same sterilizer, the temperature distribution test may have to be performed for each type and size of the container.


Heat Penetration Tests should be designed to ensure that the maximum critical factors to be tested are present in all the test packages. A representative slowest heating product may be used to establish the process for similar products.


Many processors do the processing based on a pre-defined fixed time / temperature / pressure which will be calculated based on the data collected from the validation. The come up time, holding time, sterilization time, cooling time etc will be pre-defined and process it based on a fixed time.

But how safe is this method ?

Validation strictly confirms that a specific processing procedure is pre-defined for only one type of processing for one type of product. Changes in the size or type of pouches, initial temperature, head space, product recipe, composition, orientation, loading pattern, cooling water temperature, changes in the number of products loaded in one batch etc will nullify the pre-defined validation procedure. So the processor should make sure that he is not changing any of such composition if he follow time profile for processing. Moreover in such cases, the processor should keep one specific retort dedicated to one type of products.

This way of processing eliminates the errors made by non-technical operators during the retort processing and will help to produce products with consistent quality if the processor adheres to all the required pre-determined parameters.

There are chances that the validated data might change during the course of the processing.

Validation of the retort confirms that the retort is working fine within its specifications at that specific time only. It does not guarantee that the situation remains same for the near future. A power failure, system failure, PLC complaint, sensor problem, problems at the supply lines ( steam, air , water lines etc), variation in initial temperature,  blockage of the supply lines due to rusting, sedimentation, scaling, problems with the boiler, air compressor  etc may happen at any time.  So doing validation once in a while may not guarantee that the processing is done properly.

Normally the retort manufactures use RTDs or Pt 100 sensors for monitoring the temperature of the retort medium. These will be positioned at the corners of the retort and it will not indicate the actual temperature at the middle or cold spot of the retort. The sensing elements of such sensors are big and it indicates the average temperature of the total surface area of the sensor. Moreover a small shaking or accidental fall of such sensors may create a drift in the values. So very frequent calibration of these sensors are required to make sure that it is works properly.

More over many processors use different types of products to process in the same retort. This is against the validation rule. It strictly confirms to use only one type of product for one pre-defined process procedure.

How to minimize these problems ?

To minimize these problems, it is recommended to use high accurate and reliable systems to do regular monitoring of the processing in conjunction with the validated data.

Thermocouple probes with needle probes can be used to insert into the cold spot of the containers and it could be positioned at the cold spots of each baskets. One probe for each basket is recommended.  Minimum three probes should be used in one retort.

While fixing the probes, make sure that the measuring needles are thin and it will not displace any material. Moreover the fittings should be air tight and water tight without any leakage to simulate actual processing conditions. Provision should be provided to position the measuring sensor exactly at the cold spot of the hardest piece of the products inside the containers.

Pressure probes also can be used for monitoring the pressure inside the retort.

So while doing the processing, the customer can always cross verify that the retort processing is done based on the pre-defined technology and any deviation in the pre-defined values could be detected immediately. If there is a deviation from the pre-defined value during the course of the processing, then the processor could control the retort manually to reach the required safe Fo values.

If the processor is planning to process different products in the same sterilizer, then it is recommended to use Semi – Automatic processing instead of pre-defined fully automatic processing based on time, so that any unforeseen situation during the processing could be taken care.

At least 3 probes should be used for the regular monitoring and always follow the lowest values shown by the probes. The processor should watch the monitoring data carefully to make sure that the probes are giving the correct values.

Usage of unreliable or low quality probes or machines will have negative effect on this method as a change of even 1 deg C can make a difference of 26% to the Fo values during the sterilization time ( at 121 deg C) .  So make sure that you are using high quality, most reliable equipments for the regular monitoring applications.