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Module 12. Hydrostatic Retorts 

9 CFR 431.6(b)(5) Hydrostatic Retorts 

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Purpose and Objectives 

 Purpose of Module 12 

• Provide an understanding of components 

and operation of equipment used for 

hydrostatic retorts. 

 Performance Objective 

• Assess compliance of hydrostatic retort 

equipment and perform inspections 

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Hydrostatic Retort 

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Introduction 

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 Constant process 

temperature 

 Continuous container 

conveyor 

 Steam or cascading 

water with 

overpressure 

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Processing Chamber Pressure 

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 Hydrostatic pressure 

of water columns 

counterbalance 

steam pressure 

 Maximum process 

temperature limited 

by maximum height 

of legs 

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Description of System 

Container-Conveyor: 

 Carriers for holding containers 

 Carriers limit container sizes 

 Multiple container-conveyors 

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Feed and Discharge Stations 

A variety of mechanisms are used to load and 

unload containers from conveyor. 

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Feed and Discharge Stations (2) 

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Discharge 

Dual 

Chain 

Flight 

Infeed 

Stick 

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In-Feed Section 

 Extends from feed station to entry into first 

water column 

 Section may be covered 

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Feed or Inlet Leg 

 Water column(s) prior to entry into processing 

chamber 

 Independent temperature control 

 Steam injection at base 

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Processing Chamber (Steam Dome) 

 Temperature control 

independent of 

water legs 

 In steam retorts 

referred to as 

"steam dome" 

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Discharge or Exit Leg 

 Water column(s) prior to return to atmospheric 

pressure 

 Independent temperature control 

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Discharge Leg Temperature 

 Steam injection to heat 

 Maintained by container heat (primary) 

 Cross-circulation between legs (usually done) 

 Heat exchanger to cool leg if more rapid 

cooling is desired 

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Water Circulation and Temperature 

Control 

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Container Cooling 

 Cascading water 

 Water sprays 

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Installation and 

Operation of Retorts 

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Instrumentation 

Temperature Indicating Device 

 Each processing chamber must have 

temperature indicating device and 

temperature/time recorder 

 Must be installed near steam-water interface 

3 inches above maximum water level 

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Water Leg Temperature 

When minimum temperature in the water legs is 

specified in process schedule there must be: 

1. Temperature indicating device 

2. Temperature/ time recorder 

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Temperature/Time Recorder 

 Bulb must be 

installed in 

processing chamber 

 Between steamwater interface and 

lowest container 

position 

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Steam Controller 

 Must have an automatic steam controller 

 May be recorder-controller 

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Preparation for Processing 

 Operating procedures must be documented 

by manufacturer or processing authority 

 Steam dome must be vented – The firm 

should refer to the equipment manufacturers’ 

instructions for venting or have a written vent 

schedule from their Process Authority 

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Bleeders 

Bleeders must be: 

 1/4-inch or larger opening 

 Located opposite steam entry 

 Wide open during processing 

 Arranged to observe functioning 

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Water Level Control 

 Level defines conveyor length in processing 

chamber(s) or steam dome 

 Level affected by height of water legs and 

processing chamber temperature/pressure 

 Called steam-water interface 

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Water Level 

Water Level: 

 Maximum level established by manufacturer 

Water level fluctuations: 

 Affect process time 

 Caused by containers entering and leaving 

water legs 

 Level controlled by system that adds and 

removes water to the legs 

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Process Timing 

 Container-conveyor is driven by variable 

speed motor 

 Changing container-conveyor speed changes 

process time 

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Container Conveyor Speed 

The Container Conveyor Speed must: 

 Be checked and recorded at start of 

processing and must be checked and 

recorded at intervals not to exceed 4 hours to 

ensure correct chain speed 

 Provide means to prevent unauthorized 

changes 

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Processing Considerations 

Feed and Discharge Legs 

 Time in heated water legs may be included in 

scheduled process 

 May reduce process time 

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Water Leg Temperature 

If the water leg is included in process schedule, 

the temperature must be above specified 

temperature. 

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Water Level Fluctuation 

 Process time shortened if above maximum 

level 

 Automatic device (high water sensor) should 

stop container-conveyor 

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Water Level Fluctuation (2) 

Water contacting containers in bottom loops: 

 May result in underprocessing 

 Containers must be segregated 

 Processing authority evaluation 

 Numbered carriers/diagram 

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Initial Temperature 

 Measure using method and frequency in the 

establishment’s written procedure 

 Feed leg temperature must be considered 

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Record Requirements 

 Critical factors must be measured and 

recorded in accordance with the method and 

frequency in the written procedure 

 Records must include conveyor (chain) speed 

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Key Points 

 Hydrostatic retorts use water columns to 

counterbalance the pressure in the steam dome 

 Each retort must be equipped with at least one MIG 

and time-temperature recording device, in the 

steam dome as well as in the water legs, if 

applicable 

 The water level in the base of the steam dome must 

be controlled below the maximum to prevent 

process deviations 

 Process time is dependent on the length of the 

conveyor chain and the speed of the chain 

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Questions? 

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Questions?

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