Retort processing is a new advance in making packages that have begun to transform the marketing and goods of food and beverage products. Retort technology is the solution to meet consumer’s demands that will help consumers save time and energy.
This article will discuss deeply what retort processing is, its operating principles and three main types of retort processing. You can develop a basic understanding of retorting and consider applying this process to your manufacturing.
What is the retort process?
Retort technology systems use steam or superheated water for cooking in their package
Retorting is heating low acid food and beverages 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.
Retort technology systems use steam or superheated water for cooking in their package, thus extending shelflife and ensuring safety. Manufacturers of food and beverage products who face a challenge in making their packaging products attractive should design packages with an innovative look. The revolution in packaging technology has to boost suppliers’ minds to be creative in providing convenient products to the consumer.
Read more: Top 20 great beverage packaging suppliers that you should know to enhance your beverage business
What are retort operating principles?
The retort processing techniques also differ from the normal production process.
The retort is the main processing chamber where the packed is sterilized, pasteurized or cooked properly to achieve safety and quality. The primary objective of this thermal processing is to destroy microorganisms and deactivate the enzymatic activity, which is responsible for a shortage of shelf life and changing the physical and chemical properties of the product. Retort consists of a basket in which packaged food is kept. Then these products are exposed to the sterilizing temperature mainly by applying steam, and high pressure compressed air and water for sterilizing and cooling the products, respectively. Principally, it includes seven steps.
- Preparing the retorting: Cleaning by washing and steaming, checking all the pieces of equipment before loading the cans
- Loading: Can are jumble stacked for better steam circulation, reducing the retort capacity by about 25%.
- Venting: Remove air from the retort before process timing begins.
- Come-up-time: It’s time to bring the retort to processing temperature after steam is turned on. The most critical thing is to see that all air is driven out through vents before processing starts. The vent should be closed when the processing time starts.
- Processing: If there is no automatic control, the retort temperature should not fluctuate more than 0.50C during the process.
- Blowing Down: Stopping steam income and opening the vents. The pressure should be gradually brought to ‘zero.’ Too quick blowing down may result in buckling cans. Open the retort only when the pressure reaches zero.
- Unloading: Unload the cans and cool the outside promptly.
The retort processing techniques also differ from the normal production process. Hence, the retort designs and operating principles also differ. Traditionally, metal cans were for retort processing because of their rigidity. Still, they could not efficiently transfer the heat because the product in the middle takes more time to get sterilized. Therefore, retort pouches were developed to combat this problem of uneven heating, which provides efficient heat transfer.
3 Basic retort processes:
Retort packaging is used for ready-meal production
There are three basic retort processes: steam, falling water and total water immersion. There are also subdivisions within each category, including steam/ air, steam spray, water spray and half immersion. All the processes, bar simple steam, will work on all of the current container formats, so there is not necessarily a ‘wrong’ process for novel applications. However, some principles of transferring heat to sealed containers have advantages over others when specifying particular packaging media. This is particularly so when choosing between rigid, semi-rigid and flexible formats. While the tin can is processed in all three heating mediums, plastic pouches and CPET (crystalline polyethylene terephthalate) trays used for ready-meal production have different requirements
Steam: This is the oldest form of autoclave and is usually a top-loaded, vertical pressure vessel with straightforward controls. Pressurized steam is admitted to the chamber, driving the air atmosphere out of the top of the vessel in a ‘vent’ phase lasting up to ten minutes. This valve is then closed, and the temperature is raised by injecting steam, creating overpressure from the temperature increase. Thus there is no independent control of temperature and pressure. Because the gaseous medium is not mixed or agitated, air must be eliminated during the venting phase to ensure no ‘cold spots’ – pockets where the temperature is significantly lower due to stratification – since air and steam do not readily mix without assistance. Cooling is achieved by flooding the chamber. The technology used in this type of retort presents significant challenges for modern processors. The venting procedure is expensive because up to 36% of the steam is required for the process. The pressure fluctuations mean that it is virtually impossible to process pouches, semi-rigid pots and trays without distortion of the packs or the risk of cold spots occurring if compressed air is used to create overpressure artificially. The vertical orientation of the retort means that full automation of basket loading is not achievable.
A demographic of steam retort machine
Steam/air: The steam/air process is a highly effective development of the steam process. Significant differences from the steam retort are horizontal vessels with quick-opening doors to facilitate basket loading and unloading, forced steam circulation, and, most importantly, independent temperature and pressure control. Lagarde Autoclaves patented the steam/air process in 1972. The steam is injected directly into the vessel. A reduced venting time is achieved by using a high-velocity fan to re-circulate and mix the steam with any residual air, eliminating the occurrence of cold spots. This highly efficient process was specifically developed for flexible and semi-rigid containers, initially for military rations in aluminum foil packs, but has seen many applications on stand-up pouches and ready meals. It offers rapid heating to give the shortest process times to maximize product quality. Cooling consists of two steps – a pre-cooling step that first cools the retort chamber, gradually replacing the pressurized steam environment with compressed air, and a second step that shows the hot containers with cold water re-circulated through an energy recovering heat exchanger (Figure.1). With the latest technology in automation, using robots, the production from these types of retorts is highly efficient, with short cycle times.
● Falling water
Steam/spray: This is a relative newcomer to batch retorting processes. In 1983, Surgery of Spain patented a process that combined steam and water in an atomized spray. The atomized environment gives a perfect heat transfer on rigid containers during the come-up or heating phase, as the water transfers its heat very quickly. A fan is not utilized to mix the atmosphere. Atomizing nozzles placed around the circumference of the retort take water from a pump, re-circulating the condensate, and mix it with steam directly injected into the chamber. Whilst rapid heating can be achieved, the atomizing nozzles, by their design, tend to restrict the water during cooling, leading to longer processing times than conventional cascading water, immersion or water spray types. To get around this restriction, other manufacturers of this type of retort have considered and implemented separate heating and cooling circuits to maximize the efficiency of the process.
A demographic of rain or cascading water system
Raining or cascading water: The rain or cascading water system uses superheated water to achieve sterilization temperatures under overpressure. Water is heated through a heat exchanger, pumped through a distribution plate, and showers under low pressure onto the containers below. This methodology is widely used in the processing of glass containers as the water can pass between the containers as it falls, transferring heat through the sidewalls of the container. Barriquand of France first introduced the cascading water process in 1975. The exchanger in the circuit allows steam that is used to heat the process water to be recovered as condensate, and it can then be returned to the boiler for re-heating.
● Full water immersion
Full water immersion: Another technology in widespread use is the full water immersion retort. This technology is comprised of a processing vessel and a pressurized water reservoir. Hot water from the reservoir floods the lower chamber at the start of the process and is then re-heated to sterilization temperatures. After the cooking process, the water is returned to the reservoir, ready for the following procedure. A small amount of water is retained in the processing vessel and then re-circulated and cooled through an exchanger to spray the products for cooling. Pouches and trays have tended to work against this process as the flotation of packs needs to be controlled, leading to increased costs in basket manufacture and reduced flexibility.
A demographic of full water immersion
Half water immersion: Half immersion is where the vessel is half-filled with water, and part of the rotation is in water and part out of the water. This process can give advantages when rotation speeds are high, as the cage creates less turbulence.
To wrap up
It is impossible to select a single retort process and conclude that it is optimal for every container type. However, there are distinct advantages and disadvantages when choosing a process type.
The increasing use of organic ingredients, some with high initial microbial counts, has led to decontaminating by using pasteurization or sterilization. Many foods and beverages ingredient manufacturers now use retorts as an optimal choice.
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