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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:

COMEUP VENT OPEN – SATURATED STEAM

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.

COME UP VENT CLOSED – SATURATED STEAM

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.

COOK – SATURATED STEAM

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.

PRESSURE COOL FILL – SATURATED STEAM

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.

PRESSURE COOL – SATURATED STEAM

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.

ATMOSPHERIC COOL – SATURATED STEAM

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.

DRAIN – SATURATED STEAM

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.

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22 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:

      Lacy,
      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:

    Hi,

    Can retort be used for baby food packaging?

    Thanks

    • 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:

      Calvin,
      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:

    Hi,
    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:

      Edna,
      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

    • cbarbier says:

      Sukumar,
      The overpressure will compress the air in a fragile container while a can or rigid container will support itself. We have a process control loop (Pressure Profiler) capable of detecting the amount of container deflection and correcting overpressure to minimalize this deflection. The overpressure serves different purposes in different parts of the process. In cook it allows higher process temperatures, in cooling it prevents the superheated water in the product from flashing into steam and expanding the package and damaging the hermetic seal.

  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:

      Rian,
      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:

    Sir
    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?

    • cbarbier says:

      Lammie,
      While my experience is not in the upstream processes such as washing and cleaning, I can offer some insight into the retort process. The type of retorting method used will be dependent on several factors. Container type, product viscosity, pH and protein content are all factors in determining retort process as well as whether or not you will require some form of agitation. Rigid containers like steel cans can withstand large pressure differentials. These are usually processed in saturated steam cook with an unpressurized spray or flooded cool. Others like pouches and polymeric bowls require overpressure cooling to protect the delicate hermetic seal. Protein, especially in liquid product will “burn on” to a container surface and require some form of agitation to prevent this undesirable side effect. Viscosity will determine if agitation will benefit the product. Low viscosity products such as corn in brine will benefit more from agitation than a product like pumpkin puree.

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