Canning and Fish Packaging Technology

Unit 3 - Unit operations in canning

3.2.5. Heat processing or retorting of cans
Several developments have taken place after Nicholas Appert developed canning procedure especially with respect to techniques of heat processing and the equipments used. The heating medium used is either hot water or steam and use of tools such as pressure gauges, thermometers, recording equipments etc, it is possible to subject the closed cans to precise and accurate heat process.

As most of the fruits cans are have low pH less than 4.0 (acid products), they are subjected to heat processing at a temperature less than 100^oC using hot water. Closed fruit cans are kept in boiling water for definite duration of time in boiling water, then it is cooled. This process is known as pasteurization. The equipment is known as pasteurizer. Continuous pasteurizers are available for both heating and cooling of fruit cans in which agitation cooking takes place as the cans are rotated on its own axis by rollers.
Low and medium acid foods are sterilized using steam retorts, generally, at a temperature of more than 100^oC using steam under pressure. There are several types of retorts available like automatically regulated retorts, manually operated retorts, horizontal retorts, vertical retorts etc.