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Heat penetration studies for in-pack thermal processing in batch retort systems

Identification

Key words thermal processing, sterilisation, pasteurisation, in-pack, batch retort, heat penetration, coldest point, process design, lowest lethality zone, heat distribution
Latest version 2010/12/14
Completed by KU Leuven LFT

How does it work?

Primary objective Heat penetration studies are performed to determine in the coldest spot of the product, the heating characteristics to be utilised in the design of a heat process.
Working principle Establishment of a safe in-pack thermal process in normally based on two factors: the position in the retort that results in lowest lethality (heat distribution) and the heating characteristics of the food product (heat penetration).

There are two stages in a heat penetration test: (i) determination of the coldest spot (point of lowest lethality) within the container of product and (ii) confirmation runs. Confirmation runs are based on the measurement of temperatures in the coldest spot of the container at various time intervals. Heat penetration data must be collected in the lowest lethality zone of the retort. Such experiments can be carried out on a pilot retort if the lowest lethality zone of the production retort can be simulated adequately.

Different procedures are used today to determine appropriate heating characteristics to be utilised in the design of a heat process. One approach is to determine heating characteristics for a few containers of product and use the parameters from the slowest heating container, the largest heating rate index (fh-value) and corresponding lag factor (jh-value). Another approach is to conduct heat penetration test on samples which reflect the most adverse operating conditions (e.g. overfilling containers) and use parameters from the slowest heating container in process design. A more recent approach is using the mean and standard deviation of the heating rate index in process calculations instead of the slowest single value.
No real consensus exist on what is an adequate heat penetration trial with respect to the number of test containers and the number of test runs necessary to establish a thermal process. Vague statements as ‘a large sample size is required’, ‘many runs may be necessary’, ‘sufficient data should be collected’ etc. are often reported. Of course, the number of test containers and test runs is dependent upon expected and/or observed variations in product heating rate within or between batches.

The thermal response of a product is influenced by product related factors (e.g. fill weight, product type, homogeneity of the product), container related factors (e.g. container size, shape and material), process related factors (e.g. retort temperature, rotational speed) and system related factors (e.g. heating medium, container layout). Once a process has been established for a particular food product, it is specific for that food product, its formulation, its method of preparation, the container size and layout and the type of retort system used. IFTPS (Institute for Thermal Processing Specialists) developed some useful protocols that can be used when performing heat penetration trials:

  • Nomenclature for Studies in Thermal Processing
  • Protocol for Carrying out Heat Penetration Studies
Images
Additional effects No information available
Important process parameters
  • Accuracy of the temperature data-logging equipment
  • Availability of enough temperature sensors
Important product parameters

What can it be used for?

Products Packed foods and beverages (conduction heating, convection heating and products containing particulates)
Operations Design of a thermal process for pasteurisation/sterilisation of packaged foods in batch retort systems (in combination with heat penetration data)
Solutions for short comings
  • Temperature non-uniformity in packed foods during in-pack processing in batch retort
  • Proper process design for in-pack processing of food in batch retort

What can it NOT be used for?

Products Non-packed foods
Operations No information available
Other limitations No information available
Risks or hazards No information available

Implementation

Maturity Procedures are well established (see references)
Modularity /Implementation Modularity/implementation

Heat penetration studies should be performed (i) at the time of product development and (ii) if at al later time one of the factors related to heat penetration changes (e.g. product reformulation, changes in packaging, change of retort system, change to the heat distribution performance of the retort, …).

Consumer aspects Proper process design based on heating characteristics of the coldest point of the product will result in products with optimal quality for the given processing technology, which is of interest to the consumer.
Legal aspects
Environmental aspects Proper process design based on heating characteristics of the coldest point of the product will reduce the overcooking of products and thus reduce the energy needs for the process

Further Information

Institutes KU Leuven LFT, Campden BRI, IFTPS
Companies Ellab
References 1. Guidelines for performing heat penetration trials for establishing thermal processes in batch retort systems (1997). Edited by N. May. Guideline No.16, Campden & Chorleywood Food Research Association, Chipping Campden, Glos, GL55 6LD, UK.

2. IFTPS (Institute for Thermal Processing Specialists) developed some useful protocolsthat can be used when performing heat penetration trials.

  • Accuracy of the temperature data-logging equipment
  • Availability of enough temperature sensorswarning.png"<span></span>
  • Accuracy of the temperature data-logging equipment
  • Availability of enough temperature sensors" cannot be used as a page name in this wiki.

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Created by LiesbethV on 18 January 2012, at 17:21