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Retort means any closed vessel or other equipment used for the thermal processing of foods. Typically the sterilization temperatures vary from 110 to 135°C.

Steam Static Retorts – Horizontal & Vertical
Static steam retorts were one of the first types of retort systems used to process low acid canned food, saturated steam being an excellent medium for heat transfer. It is important in the operation of steam static retorts to remove air before starting the process as air pockets can create “cold spots”, this process is referred to as venting.

Static & Rotary Steam/Air Retorts – Horizontal
For the processing of products packaged in flexible packaging e.g. aluminum & plastic trays or pouches an overpressure in excess of the saturated steam pressure at the sterilizing temperature needs to be applied to prevent the flexible packaging expanded. Steam/air retorts achieve this by the introduction of compressed air. This is mixed with the steam by a large fan at one end of the retort to prevent “cold spots”.

Static Water Immersion Retorts- Horizontal & Vertical
Another overpressure retort where the process medium is superheated water. The water level in the retort must be maintained to provide water above the top level of the containers at all times, as containers at the top might otherwise be under processed.

Static Water Cascade & Water Spray Retorts
Another overpressure retort again using superheated water. Both types are defined as retorts where a certain amount of process water is drawn from the bottom of the retort by a high capacity pump and distributed through either metal plate(s) / manifold(s) or spray nozzles located along the top and sides of the retort.


Vertical Retorts:

are identified as units, in which the crates are lowered by hand or overhead hoist into the chamber, and can vary from small one crate, to retorts holding up to four or more cages.

Horizontal Retorts:
are identified as units, in which the crates are pushed or conveyed into the chamber. They can vary from small one crate to large retorts holding twelve or more crates of product.

Rotating Batch Retorts:
are horizontal units, in which the crates are pushed or conveyed into the chamber. In order to improve the heat penetration the crates with the products can be rotated during the sterilization process.

Typical container types sterilized in static or rotary retorts include:


  • Normal and vacuum sealed cans
  • Glass Jars
  • Aluminum and plastic trays
  • Aluminum and plastic pouches
  • Glass and plastic bottles
  • Retortable cartons
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Temperature Distribution Test

The purpose of this test is to find the area within the chamber that has the minimum (coldest) temperature during the normal cycle. Anything that is placed in this area will be the last to reach the sterilizing temperature. This “cold spot” area will be where future heat penetration tests should be undertaken in the retort.
The temperature distribution test is carried out by placing a number of E-Val Pro thermocouples or TrackSense wireless loggers into the empty chamber of the retort. The temperatures within the different areas of the chamber are measured during the cycle. The area of the lowest temperature reading is defined and documented as the “cold spot” for future testing purposes.

The retort(s) selected should represent the one(s) identified as having the greatest potential for diminished delivery of the scheduled process. Factors that may help identify the test retort(s) include: retort position (at the beginning or end of a line of retorts), container configuration, divider style, and partial loads. It is often necessary to validate every retort in the production area.


Heat Penetration Test

The purpose of a heat penetration study is to determine the heating and cooling behavior of a product/package combination in a specific retort system for the establishment of safe thermal processes and evaluating process deviations, and to find the “cold spot” in the product/container, and to ensure that all products receive the minimum thermal process to deliver a safe product.

A Temperature Distribution Test should be completed before commencing the Heat Penetration Test. The goal in conducting these studies is to identify the worst case temperature response expected to occur in commercial production as influenced by the product, package and process.


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Test Equipment according to IFTPS recommendations
The calibrated system should be equipped with sufficient channels to accurately monitor and record temperature/pressure within the process delivery system. The E-Val Pro, TrackSense Pro and TrackSense Pro SKY Systems can be used where a large number of temperature channels is required. Other variables including  pressure, pack deflection, RH% and lethal values can also be displayed in the ValSuite Software Packages.

Use temperature sensors or thermocouples of sufficient accuracy in sufficient quantity to adequately monitor the process temperatures within the retort. Ellab thermocouple sensors and wireless data loggers are developed to perform very accurate measurements in retorts during sterilization.


The retort MIG or ETI must conform to applicable regulations and needs annual calibration against a nationally certified Temperature Standard within the past year. If no accurate calibration equipment is available it is possible to check the sensors in the test retort. One method of calibration is to bundle all sensors and locate them in close proximity to the known MIG/ETI.

Check the accuracy of the sensors against the reference instrument (ETI). Any single sensor should be within 0.3°C of the reference. The maximum deviation for any of the sensors should not be more than 0.6°C. The ELLAB thermocouples and data logger sensors can be calibrated to an accuracy of ±0.05°C securing accurate Lethal Value Calculations. It is important to bear in mind that an error of 1ºC of the temperature measurements corresponds to an inaccuracy of 26% in the Fo-Value at 121.1 ºC.

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Internationally Recognized Guidelines

Before doing any measurements, it is a good idea to use equipment which complies to;

  • 21 CFR 113 Thermally Processed Low-Acid Foods
  • 21 CFR 114 Acidified Foods
  • 21 CFR part 11 Electronic Signatures
  • CE & UL Approvals
  • ISO/IEC 12207 Software life cycle processes
  • IFTPS Guidelines


Positioning of Probes and Sensors – IFTPS Guidelines

  • One probe attached to the MIG/ETI temperature probe (if practically possible to enter retort and fit).
  • One probe attached or in close proximity to the Controller probe.
  • At least two probes in containers filled with the testing medium for obtaining the initial temperature.
  • A minimum of three probes each located in separate areas of each basket or crate in steam and Water Immersion Retorts.
  • A minimum of five probes each located in separate areas of each basket or crate in Water Spray and Water Cascade Retorts.
  • One pressure sensor recommended.
  • Depending on the processing system it may be necessary to place additional thermocouples in the vessel to adequately monitor the cold spot in the retort.
  • Temperature Distribution Tests should be repeated to ensure validity of data.
  • If differences between first two runs a third run must be performed.
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Choosing the System

An E-Val Pro thermocouple system has the advantage of being a real-time system, but it can be time consuming to install the thermocouple probes. It may also be difficult to avoid the thermocouples getting damaged during loading and unloading particularly in automatic load/unload retort systems.

A wireless data logging system could be used where the loggers are recording the process data which is downloaded after the process to the computer. This is easier and faster to install in the retort. The TrackSense Pro data logger system is suitable for this. To have real time measurements the TrackSense Pro SKY data logger system can be used. Another advantage with TrackSense Pro System is  using dual sensors, both Temperature Distribution and Penetration can be performed simultaneously.

Documentation – Standard ValSuite Reports

  • Comments: Specifications and test equipment
  • Limit Report: Temperature, Pressure, F0-Values
  • Time Event Markers: CUT, Equilibration, Holding, Cooling
  • Advanced Validation Report: Temperature, Pressure, Fo-Value evaluation of the whole process criteria’s with pass/fail indication
  • Statistic Reports:Min, Max, Average, Delta of all parameters
  • Heat Penetration: Ball Calculations
  • Word Documents
  • Unit: Graphics or photos showing probe position


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ValSuite® Software Reports

Retort Sterilization

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Process Graph
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Limit Report
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Advanced Validation
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Unit Report
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Heat Penetration
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