Retort Technology in Food Processing Industry
“One of the major advantages of retorting ready-meal package is that both food and package are thermally processed together, which allows the filled packages to be commercially sterile.”
What is Retorting?
Retorting is heating of low acid foods prone to microbial spoilage in hermetically sealed containers to extend their shelf life. The goal of retort processing is to obtain commercial sterilization by application of heat.
Advantages of using retortable flexible containers
01. Rapid heat transfer and hence, reduction in processing time
02. Fewer nutrient losses
03. No refrigeration or freezing required
Packaging Material
Foods can be sterilized in rigid containers like glass, metal cans and plastic or flexible retort pouches.
Cans and glass jars
Metal cans and glass jars are widely used for retort processes, because of their high mechanical strength, thermal stability, resistance to pressure, and excellent barrier properties.
Retortable plastic container/ Pouches
A typical retort-able plastic container is made of an oxygen barrier layer such as ethylene vinyl chloride (EVOH) or polyvinylidene chloride (PVdC) sandwiched between two polypropylene layers.Flexible retort-able pouches are laminated structures that must provide excellent barrier properties for long shelf life, seal integrity, puncture resistance and must withstand rigorous thermal processing.
“The materials for retort pouch must be inert, heat sealable, dimensionally stable and heat resistant (usually 115°C–125°C). They should have low oxygen and water-vapour permeability and be physically strong to resist penetration by the foodstuff contained and abuse during handling and storage.”
Steps involved in retort pouch processing include:
1. Printing the polyester film
2. Filling the pouches with the raw material
3. Removal of air
4. Sealing of pouch
5. Traying
6. Processing (Using autoclaves, steam, steam spray,water spray, etc)
The quality assurance for retort pouches is usually assessed according to the following tests:
1. A visual assessment is done by qualified, experienced personnel to make sure that the pouch is correctly formed and that there are no channels through the seals.
2. Seal strength is measured (usually mechanically) and must comply with specification.
3. Bond strength of the various laminate layers is assessed by physically tearing the layers apart.
4. Burst strength of the pouch is measured by filling it and then subjecting it to a specific force.
5. Oxygen permeability and water transmission rates are measured on bag samples before and after processing.
Commercial Application of Retort Technology
Retort technology can be applied to process ready meals, sauces, marinades, vegetables curry, soups, and rice.
Some of the popular commercial products include:
• South Indian food such as Upma, Sambar
• Biryani, fried rice
• Ginger Garlic paste