Heat Penetration

retort packagingA heat penetration test is conducted to determine the heating and cooling characteristics in the coldest point of a given product, in a given container, under specified process conditions. usually at the coldest zone of the retort .The cold spot of the product is the point inside the product where it experiences minimum heating effect during processing .The cold spot of the container is the area inside the container where it experiences minimum heat effect during the processing.

It depends on the type of container and the orientation.

Here you can see the different types of probes, sensors, tools, fittings, fixtures etc to measure the temperature at the cold spot of different types of containers.

The important thing to note that the connections should be air tight and water tight and the sensors should be as thin as possible. The measurement should simulate the actual processing conditions.

Photos courtesy to ELLAB A/S Denmark

There are many factors that can impact on the efficacy of a thermal process but one of the main considerations in the development of processes for heat preserved foods is the acquisition of accurate time/temperature profiles.The main reasons for this are:• Safety – ensuring that microbial stability has been achieved and there is no risk of food poisoning or food spoilage

Optimisation – reducing process times to increase production throughput and minimise energy costs

Improvement of quality – optimisation of vitamin and protein retention, and product sensorial qualities

Process validation – providing documentation to demonstrate compliance with regulations for authorities, FDA/USDA, EC, customers, ISO9000, HACCP, etc.

The validation procedure encompasses many aspects with the process vessel and product both needing detailed study. In both cases it is important to find the cold zone at which the slowest heat transfer will be applied.Three phases of tests should be considered:• Temperature distribution – temperature mapping within a fully loaded process vessel to investigate performance against a control programme and identify the cold zone.

• Cold point determination – multiple measurements within a product container to fi nd the slowest heating point within the product. This will be product and packaging dependent.

• Heat penetration – replicate measurements with temperature measurement devices located at the position identifi ed within the cold point tests.

All of the above phases are focused on identifying the worst case conditions to which a product would be exposed, with the lowest temperatures and slowest heat transfer leading to the lowest microbial reduction.

It is therefore crucial that the temperature measurement devices are of high accuracy and reliability.

A systematic or experimental error of 1°C in a temperature measurement system at the sterilisation
reference temperature of 121.1°C would lead to a corresponding error of 26% in the calculated Fo sterility value.It is therefore important that the correct equipment is applied for a given validation.

• Correct positioning of the measuring point

It is very important that the packing gland and probe are correctly positioned in the “cold spot”. If this is not obtained it can result in “false” measurements, risking high Fo / Po-Values.heat-penetration-calculation

Elimination of steam and water ingression

It is very important that the packing gland and the probe are mounted so as to maintain the integrity of the container and ensure that water/steam ingression to the measuring point cannot occur leading to false data and high Fo/Po values.

• Minimizing risks of heat conduction

It is recommended that the probe and gland are mounted from the side of the container with the longest distance to the “cold spot” so that heat conduction from the water/steam is avoided. Even if the probe/gland is as small as possible and made of materials with the lowest conductivity there will always be a risk for heat conduction.

• Minimizing the probe assembly inside the container

It is very important that the probe and gland are as small as possible so that the impact on the internal environment (product) of the container, including the headspace, is minimised. This is especially important for products that receive a rotary process where the movement of the headspace will be a critical factor in the rate of heat transfer.

If it is a mixed product in liquid it is important the biggest piece of solid is positioned at the measuring point, and that the probe assembly is mounted so it is not preventing the other solid pieces to move freely. The reference container must be as close to the “normal” containers as possible, otherwise the heat transfer profile will no longer be representative for the entire batch.

ELLAB A/S Denmark have developed a large selection of probes, sensors, packing glands, and tools which are available for correct mounting in many styles and designs of container.

Some of them are listed below





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