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The Allpax Horizontal Steam Retort

The Allpax Horizontal Steam Retort

The Saturated Steam Process is the oldest method of in-container sterilization. Since air is considered an insulating medium, saturating the retort vessel with steam is a requirement of the process. It is inherent in the process that all air be evacuated from the retort by flooding the vessel with steam and allowing the air to escape through vent valves. There is no overpressure during the sterilization phases of this process, since air is not permitted to enter the vessel at any time during any sterilization step. However, there may be air-overpressure applied during the cooling steps to prevent container deformation.

Note on Terminology

In the Allpax retort control system there is terminology for an Uncleared Deviation or a (Cleared) Deviation condition that may exist. These terms are referred to in this paper. The definitions of these terms are as follows:

  • CLEARED DEVIATION – When a deviation occurs, it may be possible to correct the process by adding time and/or temperature in order to compensate for the deviation. If this correction can take place in the retort, then the batch is declared to have a Cleared Deviation status. The Cleared Deviation status notifies the retort operator that a deviation was detected, but that corrective action was taken to compensate for the deviation (see Scheduled Process / Alternate Process definition). As in all cases, release of the product is subject to final review by the plant’s Quality Manager or Process Authority.
  • UNCLEARED DEVIATION – When a deviation occurs in which an unsafe product condition exists and cannot be corrected for, then the batch is declared to have an Uncleared Deviation status. The Uncleared Deviation status notifies the retort operator that a deviation was detected and continues to exist in the batch.

Process Steps

Batch retorts execute a series of programmed process steps (also known as segments). These steps must be properly executed to achieve a sterilization process that meets the regulatory requirements imposed for food safety.

In a Saturated Steam process these steps are:

  1. Come Up Vent Open (A Sterilization Step)
  2. Come Up Vent Closed (A Sterilization Step)
  3. Cook (A Sterilization Step)
  4. Pressure Cool Fill
  5. Pressure Cool
  6. Atmospheric Cool
  7. Drain (Not Recipe-Configurable)

The following is a detailed description of each step:


The purpose of this step is to saturate the vessel with steam, and to eliminate all air that may have been trapped in the retort. This step is accomplished by opening the vent valve and opening the steam control valve (and, if configured, opening the steam bypass valve.) An established vent time and temperature has been determined for the retort and product that is being processed. Since venting is both retort and product-specific, each product may have its own vent schedule, which will be incorporated into the product recipe. This information has been filed with the appropriate regulatory agency (FDA or USDA).

In order to successfully complete this phase, both time and temperature conditions established in the filed process must be met simultaneously. At the end of the scheduled vent time, the retort must be at, or above, vent temperature. If these conditions are not met, the vent time may be extended so that the vent temperature can be reached, without creating a deviation. Should the actual process be advanced to the next process step without satisfying both conditions simultaneously, then an Uncleared Deviation condition is created.

It is also imperative that the vent valve be open for the entire vent step. An open switch on the vent valve is provided for this positive indicator, as well as a vent closed switch. Should the vent open switch be seen as “not made,” or the “vent closed” switch be seen as “made,” or if both switches are seen as both “made,” at any time during the Vent Step, an Uncleared Deviation condition is created.

If water in the retort is detected at a level that is high enough to reach the bottom of the retort basket, an Uncleared Deviation condition is created.


During this step, the vent valve is closed and the temperature is controlled and ramped to Cook Temperature (unless multiple Come Up Vent Closed steps are utilized.) In order to successfully complete this phase, both time and temperature conditions, established in the recipe must be met simultaneously. At the end of the scheduled come-up time, the retort must be at, or above, scheduled cook temperature. If it does not meet these conditions, the step time may be extended so that the recipe temperature can be reached, without creating a deviation. Should the actual process be advanced to the next phase without satisfying both conditions simultaneously, then an Uncleared Deviation condition is created.

If water in the retort is detected at a level that is high enough to reach the bottom of the retort basket, an Uncleared Deviation condition is created.

Should the actual process be advanced to the next phase without satisfying all conditions simultaneously, then an Uncleared Deviation condition is created.


The purpose of the Cook Step is to maintain the recipe temperature for the time required by the recipe. In order to successfully complete this step, the temperature condition established in the recipe (the filed process) must be met for the length of time defined for the step. Should a temperature drop occur at any time during the step, then a temperature deviation condition is created. Should an alternate process be available when a temperature deviation occurs, then the batch is labeled as a Cleared Deviation. Should the alternate process(es) not be successfully administered, then the Uncleared Deviation condition for the batch is created.

During this step, the operator is required to make operator entries: at least one check and entry of the MIG reading entry, one for the Chart reading, and one for the Bleeder Valve check. All operator entries must be made for the step to be completed.

During the Cook Step of a saturated steam process, the batch may be declared a Temperature Deviation or an Uncleared Deviation after the MIG / RTD comparison check is made.

During the Cook Step of a saturated steam process, the batch would be declared an Uncleared Deviation if the operator made an entry that indicated a bleeder valve failure after making a visual check.

During the Cook Step of a saturated steam process, the batch would be declared an Uncleared Deviation if water is detected at a height sufficient to reach the bottom of the basket.


This step begins the cooling process. The cooling water enters the retort as overriding pressure control is initiated. In the initial phase of this step, steam is collapsed by the cooling water, which is displaced by large quantities of air. As the vessel fills, pressure will build as the air is compressed by the rising water level. The BPR valve is used to relieve excess pressure while the air valve is used to make up pressure.

When the water level, defined in the recipe, is reached (normally at the top of the basket), the step ends.


This step continues the retort cooling process. Cooling water continues to flow into the Process Vessel and flows out through the drain valve, which controls the level. Control to the recipe pressure setpoint is maintained using the Pressure Relief valve and Air (Pressure Makeup) valve with a dead-band of .5 to 1.0 psi. When the pressure cool time is completed and the recipe temperature is met, the step ends.


This step continues the retort cooling process. Cooling water continues to flow into the Process Vessel and flows out through the drain valve, which controls the level. Control is removed from the Pressure Relief valve, releasing pressure by opening the vent valve (note: pressure may be steadily released using ramp control employed in a second Pressure Cool step). When the atmospheric cool time is completed, and an established temperature setpoint in the Process Vessel is achieved, the step ends.


This step drains the water from the retort. The drain is opened the water gravity-drains from the retort. When the level condition is met, the step ends. Note: To accelerate the drain step, limited overriding air pressure (2-5psi) may be used during the step.

A complete line of retort room equipment, including horizontal saturated steam retorts. See Allpax Steam Retorts.


33 Responses to “Understanding the Retort Sterilization Process – Steam Retorts”

  1. Zuzana Ticha says:

    I would like to ask you for a price offer for water spray retort.
    If you will need more information- do not hesitate to contact me

  2. Shashank Athwani says:

    What is the difference between retort and autoclaving?

    • Both words refer to the process of sterilizing a given item. This item could be medical instruments, a sealed container of food, or anything else.

      So there is no difference between these two terms. They are two different ways to say the same thing.

      • geneille says:

        is retort machine advisable to replace autoclave in microbiology laboratory?

        • cbarbier says:

          A retort is an autoclave. The difference here is that our retorts can perform various processes i.e. water spray, water immersion and steam-air in addition to saturated steam with or without horizontal or rotational agitation.

  3. Lacy says:

    Hello I need a little help understanding the difference between the retort process and canning. Is the difference in process that retort only uses pouches or can you retort with cans as well or is it that retort seems to only uses steam to sterilize the food where canning seems to work by placing jars or cans in water and boiling the product before sealing…

    • cbarbier says:

      The retort process is that by which a product is rendered “commercially sterile” by processing a hermetically sealed container in an over-pressure(above atmospheric) environment. Canning is the process of preparing a product, placing the product in a hermetically sealed container and thermally processing it so that it is shelf stable at room temperature for extended periods. Therefore retorting can be part of the canning process. Factors such as the pH and water content of the product among others determine the temperature and duration at temperature the product requires. Hope this helps.

      • Rahul Jain says:

        According to the definition of retort process as you defined, is it just the over-pressure which makes a given item sterile or the thermal treatment also. because if over-pressure is the only force here then it should be called high pressure procesing.

        please mail me : jainrahul2910@gmail.com

  4. Bluesalt2009 says:


    Can retort be used for baby food packaging?


    • cbarbier says:

      Thank you for your inquiry. The answer to your question is yes. Water immersion retorts are used for glass bottles while water spray retorts are used for fragile and flexible packaging.

  5. Calvin says:

    Dear Sir,
    Impressive range of retort machines you have in your website! Congratulations!
    We are manufacturing Asian sauces with preservatives added.
    Moving forward, we plan to take out preservative from all of our products.
    Target shelve life is 24 months, on normal room temperature between 25-30 Celsius.
    We would like to enquire if our products need to be retorted.
    pH level for all of our products range between 4 to 7
    Water activity between 0.8 – 0.95
    Some of our products contain oil as part of its ingredients, some products are not.
    Another question if I may ask, why some products are shelf stable for 24months even not retorted while some products need to be retorted.

    We plan to pack our products in retort pouch and will manufacture can food soon.
    Please advice if you have 1 retort machine that is suitable for both pouch and can food.
    Thank you sir and looking forward to hear from you soon.

    • cbarbier says:

      Please refer to our website and research the dual mode, water spray/saturated steam production retort. It is designed specifically for your application.

  6. Angela says:

    Hi! Do you have an alternate process in case steam is not stable?

  7. Edz says:

    We are processing smoked sausages in natural, collagen casing with shelf-life of 90 to 105 days, and wanting to know if through retort process / cooking could be possible for our sausage products considering using the heat tolerance casing.
    Thank you.

    • cbarbier says:

      A “commercially sterile” low-acid product will be subjected to a thermal load of at least 120°C for a minimum of about 6 minutes at its cold spot. The exterior regions will receive more. Only testing will determine if the quality is affected. Suffice it to say that most if not all low-acid ambient stable foods will be overcooked. There are processes like aseptic fill and microwave as well as our Shaka process which seek to minimalize the thermal load duration thereby retaining the desirable attributes of food. Please feel free to contact me if you wish to discuss this further.

  8. sukumar says:

    We are looking for a retort machine for production of ready to eat Mushroom and Broccoli products. My querry is what happens to the air inside the can or pouch since the pressure cooking is done after sealing of pouch or can

  9. Rian says:

    Hi, i want to ask about “come up vent open”. how many minute this step if we use small retort for example if the diameter is 1 meter and the high is 1 meter.

    Thank you

    • cbarbier says:

      The length of the “come up, vent open” step in a saturated steam process is determined in several ways. One method is to place an oxygen sensor in the vent to detect air. Another is to place a thermocouple in the vent to detect temperatures equal to saturated steam temperatures. Lastly is to perform a temperature distribution to detect temperatures within the retort load allowing for saturated steam temperatures to be reached in the “cold spot” of the retort load. Each or any combination thereof is performed by the process authority prior to production.

  10. Lammie says:

    I am a vegetable farmer and are investigating methods to process the vegetables to extend the value chain of our business. I am producing vegetables like sweet corn, potatoes, beetroot, pumpkin, carrots etc. I am investigating the retort process of preservation of the products, but I need some information on what retort method will be best, as well as other processes needed to prepare the veggies for retort like washing, blanching?

    Can you help with information, or where/who can give me the necessary information?

  11. Daren Shaw says:

    Hi I’m looking at options for packaging soup and sauce products and equipment required.
    Thanks in advance,
    Any advice would be greatly appreciated.
    Daren Shaw.

    • cbarbier says:

      Thank you for your interest in Allpax Products. As you may have seen on our website, we specialize in all retort room operations including material handling. In order to determine which type and size retort your project will require, I will need some additional information.
      • What type of container will you be using and what are its dimensions?
      • What is your line speed in containers per minute?
      • What is the total process time including loading, come-up-to-temperature step, cook or hold step, overpressure and atmospheric cooling steps and unloading?
      • What degree of material handling automation do you wish to have?
      In addition to the retort room, within our holding company we have sister companies which can provide numerous services from pouch filling and sealing, bottle filling and capping, shrink wrapping, container coding, case forming and packing, pallet forming and stretch wrapping and a host of other facets of your packaging needs. I look forward to assisting you in your upcoming project.
      If it’s in the Retort Room, WE’VE DONE IT!
      Chris Barbier, Technical Sales
      Allpax Products, Inc. a division of Pro Mach
      13510 Seymour Myers Blvd
      Covington, LA 70433
      985.893.9277 Ext. 124 Voice
      985.893.9477 Fax

    • cbarbier says:

      There are several options for packaging which include steel cans, glass bottles and polymeric pouches and bowls. These different types of packaging will utilize different types of retort processing. In addition, there are agitation options which can shorten process times and improve product quality. Please contact me for specific applications and requirements.

  12. We have plan to start cans food products can I use for normal steem retort I have this machine

    • cbarbier says:

      I assume you are asking if a saturated steam retort can be used for processing steel cans. If that is the case, yes it can be used.

  13. Wawa says:

    Hi there 🙂

    I’m currently having a problem with the post-retort products (metal cans) which they’re prone to rusting after being taken out from the retort machine. We’d tried to increase the venting time but still the rust appeared on the exterior part of the cans. Pls help.

    • cbarbier says:

      Steel cans like any other steel component will “rust” when exposed to oxidizers, the obvious one being oxygen. There are others which may be present in your water supply. The halogens (chlorine, fluorine etc.) as well as inorganic peroxides will have the same effect on untreated steel. Check your water source and be sure that you are not leaving any standing water on the containers as they are stored.

  14. Jose Thomas says:

    we want retort jackfruit raw and ripe. Is it possible to retort the same without heating the jackfruit and thereby maintain the naturality. Thank u

    • cbarbier says:

      Retorting (commercial sterilization) which is the destruction of non-vegetative bacterial spores requires thermal processing at temperatures at or near 121 Celsius. Therefore you can not retort a product without heating.

  15. cbarbier says:

    Fragile containers require overpressure during the heating and cooling phases, therefore, you will require a water spray, water cascade water immersion or steam-air process with overpressure.

  16. cbarbier says:

    Modifying thermal processes is typically performed by a company designated process authority because calculating microbial lethality is done using specific formulas. Under processed LACF’s (low-acid canned foods) pose a great liability to a food manufacturer.
    Factors which can prolong heating and cooling phases of a thermal process include; type of agitation (or lack thereof), product initial temperature, container material, capacity of the boiler and utility (cooling) water temperature and flow rates, among others.

  17. safia says:

    Means distilled water should be used??

  18. Elisabeth says:

    Can you explain me what it means “end-over-end” retorts?

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