Retort Processing

INTRODUCTION  ​

  • The demand for ready-to-eat processed food is skyrocketing in emerging nations like India due to changing lifestyles, rising job demands, and nuclear families.​
  • Thermal processing is one of the most important methods for producing packaged, shelf-stable food goods. ​
  • Food preservation through canning has advanced to include the retort processing of foods in semi-rigid, flexible laminates. It is a thermal procedure that gives products a longer shelf life while maintaining appropriate nutritional and sensory properties [1]. ​

Types of Retort ​​ 

The three fundamental retort processes are​

  • Steam​
  • Total Immersion. ​
  • Falling Water​
  • Each category has further subcategories for steam/air, steam spray, water spray, and partial immersion. ​
  • When choosing a particular packaging medium, it is evident that some principles of heat transmission to sealed containers have benefits over others [2].​

Steam Retort​  

  • The first technique for in-container sterilisation is the saturated steam process. ​
  • The technique requires the retort vessel to be saturated with steam since air is considered an insulating medium.​
  •  It is necessary for the procedure that all air be let out of the retort by filling the vessel with steam and opening vent valves. ​
  • Since air is not allowed to enter the vessel at any point during any sterilisation stage, there is no overpressure during the sterilisation steps of this procedure. ​
  • Air overpressure may be supplied throughout the cooling process to avoid container deformation [3].​

 Saturated steam retorts

Water Immersion Retort​​   

  • The water immersion technology is the overpressure technology most frequently used to sterilise products. ​
  • The product is completely shielded from any impact of cooling air during the water immersion process, similar to a saturated steam process in which the product is completely submerged in water. ​
  • In contrast to saturated steam, air can be injected into the vessel during sterilisation, adding air (or steam) on top of the water creates overpressure. ​
  • In some cases, the steam is heated by the addition of air; the hot air pressurises the processing load and stirs the water as it rises to the surface [4].​

Water-immersion-retort

Water Spray Retort ​​    

  • Like water immersion, the water spray method likewise uses overpressure, but the product is subjected to the effects of overpressure air. ​
  • In water spray retorts, steam is the driving force for getting to the centre of the load, and it is comparable to the saturated steam process. ​
  • Air can enter the vessel during sterilisation with the Water Spray method, unlike saturated steam, which cannot. ​
  • By injecting air (or steam) into the retort, overpressure is created. The spray nozzles vaporise the steam and combine it with the air to overcome the insulating properties of the air [5]. ​

 

Water-spray-retorts

Retort Pouches ​    

  • The Reynolds Metals Company, Continental Flexible Packaging, and the United States Army Natick R&D Command developed the retort pouch. ​
  • A retort pouch is made of laminated plastic and metal foil with three or four wide seals typically produced through aseptic processing. This makes it possible to package a wide range of beverages in a sterile manner, including everything from water to fully prepared, thermostabilised meals like ready-to-eat meals.  ​
  • Using this method, cooked or raw food is first prepared and then sealed in a retort pouch.​
  • The pouch is heated inside retort or autoclave machines to 240–250°F (116–121°C) for several minutes under high pressure. This method reliably eliminates all typically present microorganisms, especially Clostridium botulinum, preventing spoilage [6].​
  • Propylene, the first layer, is a heat-seal surface and offers strength and flexibility. ​
  • The nylon layer, which is the following layer, provides abrasion protection. ​
  • The aluminium coating enhances the product’s shelf life and shields it from light, gases, and odour. ​
  • Excellent strength is provided by the last polyester layer, which is also extremely simple to print on. In addition, FDA-approved materials are used for packaging retort pouches, and sterilisation procedures boost the packaging’s tensile strength [7]. ​

 

Schematic diagram of a retort pouch

Advantages ​    

  • Different sizes and shapes​
  • Improved graphics capabilities;​
  • 85% reduction in empty weight and space; lower cost per pouch; ​
  • Easy, safe, and less expensive transportation; ​
  • Shelf life equal to or better than cans; ​
  • No refrigeration or freezing; ​
  • Easy opening facility;​
  •  Environmental safety; ​
  • Destruction by incineration; ​
  • Easy reheating before consumption; ​
  • No refrigeration or freezing​

Disadvantages ​​

  • Not as durable as cans, ​
  • Higher packing costs lower processing line speed; ​
  • Higher investment cost; ​
  • The possibility of rodent and insect assault and challenging leakage detection [7].​