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Hydrostatic retort for continuous in-pack thermal processing


Key words pasteurisation, sterilisation, thermal processing, continuous retort, hydrostatic retort, packed foods and beverages
Latest version 2010/12/14
Completed by KU Leuven LFT

How does it work?

Primary objective Continuous thermal pasteurisation or sterilization of packed food products using a hydrostatic retort
Working principle The essential principle of a hydrostatic retort is the use of hydrostatic columns of water of sufficient height to counter-balance the pressure of the steam used in the sterilization zone. A typical hydrostatic retort consists of a preheating leg, a steam sterilizing chamber and one or more cooling legs. However, there are many different arrangements of the legs, depending on the nature of the product being thermally processed.

The packages are transported on long horizontal carrier bars (which may or may not impart rotary motion) chained together. The carrier bars enter the preheat leg at the top and progress down until they reach the steam chamber, where they make at least one double pass before emerging upwards through the cooling leg. The chain speed of the carrier bars determines the sterilization time, and can be varied as needed. An automatic loading and unloading system brings the containers in and out of the carrier bars. An hydrostatic retort is available in either a container-dedicated or a super-flexible execution. In pure steam hydrostatic retorts, the sterilization temperature is directly related to the pressure of the saturated steam. By varying the pressure, the temperature can be controlled. Nowadays, hydrostatic retorts using superheated water cascading with air overpressure and pressure preheating and cooling are available.

Additional effects As a hydrostatic retort is a continuous retort, a high throughput can be realized, ranging from 60 to 2000 containers per minute.

As they are vertically oriented, they require relatively little floor space.

Important process parameters temperature, chain speed of carrier bars (time)
Important product parameters thermal diffusivity, geometry and dimensions, viscosity, head space

What can it be used for?

Products Food industry: packaged foods and beverages

An hydrostatic retort is ideal for processing products that require long cook and cool times, high throughputs and for those deriving limited benefit from agitation

Operations Thermal pasteurisation or sterilisation of packaged products
Solutions for short comings This technology solves the problem of low productivity of batch retort and provides better temperature uniformity in packed product by moving the packages in heat transfer media.

What can it NOT be used for?

Products Not suited for non-packed products
Operations No information available
Other limitations This system is not flexible for changing demands on sterilisation time of different products (the system has to be emptying first before introducing new product).
Risks or hazards No risks/hazards


Maturity Available at industrial scale
Modularity /Implementation As an hydrostatic retort requires a dedicated loading and unloading system, it replaces the major part of a production line.
Consumer aspects No information available. No problems expected.
Legal aspects No information available, but no regulatory hurdles are anticipated.
Environmental aspects No information available. No problems expected.

Further Information

Institutes Campden BRI, KU Leuven LFT
References Holdsworth, S.D. (1997). Thermal processing of packaged foods. Blackie Academic & Professional, London, pp. 283, (ISBN 0 7514 0375 X)

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Created by LiesbethV on 29 January 2011, at 02:43