• Retorts/Autoclaves
  • Shuttle And Loading/Unloading Machine
  • Vacuum Fryer

Thermal Processing Methods For Food Preservation


Basic food preservation involves either destroying spoilage and disease-causing microorganisms or inhibiting them from growing. Microorganisms are present on virtually all raw food ingredients, but since they are living organisms, they cannot grow under adverse conditions and will die if their surroundings become unfit. The most easily regulated feature of their environment is temperature, although other sterilization agents such as chemicals or high energy radiation may be used. Simply stated, thermally processed foods are typically preserved by using heat for a certain length of time to kill the microorganisms present in the food and by using a sealed container to prevent recontamination of the food.

cans being prepared for use in heat penetration test

Two different methods are used to produce canned foods: conventional canning or aseptic processing and packaging. For conventional canning, the product is filled into the container, the container is hermetically sealed, and the container and product are thermally processed together. For aseptic processing, packages and food product are sterilized in separate systems. The sterile package is then filled with sterile product, closed and hermetically sealed in a sterile chamber. Either of these methods may be used for acidified or low-acid products.

Canned foods are processed to a condition of 'commercial sterility' or as it is sometimes referred to," "shelf stability." Commercial sterility is defined as the condition achieved by application of heat, sufficient, alone or in combination with other ingredients and/or treatments, to render the product free of microorganisms capable of growing in the product at normal non-refrigerated conditions (over 50°F or 10°C) at which the product is intended to be held during distribution and storage.

Many methods exist for delivering the thermal process for commercially sterile products. These thermal processing methods will vary depending on whether the processing method is conventional canning in a retort, aseptic processing, or pasteurization techniques for acidified products. There are various retort systems and aseptic processing and packaging systems, but we only discuss retort systems herein.


Retort Processing

In simplest terms, a retort is a closed pressurized vessel used for heating foods sealed in containers. Many different retorting systems are used for processing commercially sterile foods packaged in hermetically sealed containers. Retort systems have a few common characteristics.


The systems are pressurized and the temperatures delivered are much higher than boiling water. The systems use a medium (referred to as heating medium or processing medium) as the means to transfer heat to the product. The heating media used in retorts include pure steam, hot water (with the containers being completely immersed in water, sprayed with water or cascaded(showered) with water), and steam/air mixture.

Some systems provide overpressure during processing and cooling to maintain the integrity of containers and counterbalance the buildup of pressure inside the container. This may be necessary because some packages have limited resistance to internal pressure. Some examples of containers processed with overpressure are semirigid plastic containers with heat sealed lids or metal double seamed ends, flexible pouches, metal trays, paperboard containers, and glass jars. The term “overpressure” refers to the pressure supplied to a retort in excess of that exerted by the heating medium at a given process temperature. In a steam retort, the pressure at 250°F is about 15 psig (pounds per square inch gauge); any pressure supplied to the retort in excess of that 15 psig is referred to as overpressure. Retort systems providing overpressure will operate at higher pressures, for example 25-35 psig.

The retort must be operated properly to ensure that the containers are processed to achieve commercial sterility.

Innovaster custom designs and manufactures solutions of all types of retort processing systems starting with your containers. More on commercial sterilization, please contact with our sales consultant.


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