What is retorting, and why is it done?
Retorting is a process where food is heat-treated inside the package. The heat treatment is applied to generate a commercially sterile product that is stable in ambient conditions prior to opening.
Can paperboard-based carton packages be retorted?
Yes, carton packages can be retorted just like tin cans, glass jars and plastic pouches. The retortable carton is a one-piece container that is filled unsterile and is processed after the container has been sealed. The flat carton-fed system enables filling of a large range of viscous product and particle sizes dependent on the type of filler and machine platform used. It has a laser perforation to enable easy full-top opening of the package.
How does the retorting process work?
Food preparation can include steps such as peeling, cutting, blanching, soaking, frying mixing and so on. The prepared food product can be filled into the carton package in one or multiple steps, depending on the food type and the selected filling solution.
After sealing, the carton package is then heat-treated in a retort, also known as an autoclave, to achieve a commercially sterile product.
At what temperatures is food retorted, and for how long?
The ultimate aim is to produce safe food products of high quality. So the temperature and retorting time required for a specific food product needs to be thoroughly evaluated before being implemented. Generally, 121.1°C is required for sterilization. For products with pH below 4.5, pasteurization temperatures can be applied. A normal retort process usually takes between 60 and 180 minutes in total.
Are all products heat treated in the same way?
The goal when retorting is to retain the highest possible product quality without compromising on food safety. By using the lowest possible temperature in combination with the shortest possible heating time, the product is kept fresh. Therefore, the heat treatment process is optimised for each product.
Learn more about the heat treatment process in our infographic Understanding heat treatment.
What food products can be retorted in carton packages? Are there any limitations?
Tomato products, beans, fruits, vegetables soups, ready meals, baby food and even petfood can be found in carton packaging today. The process is ideal for any food that can be sterilised or pasteurised to make it safe on a microbial level. Limitations relate to if the food can maintain its taste and freshness after heat treatment.
Are there alternatives to retorting for shelf-stable food?
Yes – a continuous processing line with aseptic filling of carton-based packages. This method is commonly used for beverages and dairy products but is also suitable for viscous foods. The food product undergoes heat treatment in a steriliser, before being filled in sterilised packages in a completely aseptic environment.
The main difference between these packaging solutions is that a retortable carton is constructed to fully process the product inside the package when sealed, while aseptic packaging maintains a product that has been fully processed before filling. Both packaging solutions include barriers to maintain high product quality during shelf life.
What does the packaging material for retortable carton packages consist of?
It is made of six layers: four of polypropylene, one of aluminium, and one of paperboard. Paperboard – a renewable material – makes up at least 69% of the package.
The structure enables the material to withstand water exposure during the retort process and provides a suitable environment for a wide variety of products, while meeting demands for a long shelf life.
What are the sustainability credentials for retortable cartons?
It depends on the retortable carton, but typically, they offer a lower carbon footprint than cans and jars of equivalent sizes, while also being more logistically efficient. Cartons such as Tetra Recart® are also made up of up to 71%* renewable materials that come from responsibly managed sources.
In terms of carbon footprint, the carbon emissions from Tetra Recart over the lifetime of the package are 85% lower than steel cans, and 83% lower than glass jars**.
Regarding logistics, it’s typically possible to fit 10-20% more filled packages per truck, as the square shape means they stack more efficiently. With empty packages, it’s even more efficient, allowing for six to ten times more Tetra Recart packages to be transported on a single truck. This can contribute to reduced carbon emissions, as fewer trucks are required to transport the equivalent amount of packages and product.
What equipment is required for retorting carton packages?
The machine that heat-treats the package for sterilisation purposes is known as either a retort or an autoclave.
Steam water spray retorts are commonly used for retortable cartons. The retort equipment is standard for the industry, but the packages require a specific rack to enable an even heat treatment during processing, while maintaining the integrity of the packages.
During the retort process, it is important to maintain an outer overpressure high enough to balance the internal pressure in the package generated by the food product. Too low or lost pressure in the retort during processing will result in package deformation. Controlling the overpressure in the retort is important in all processing steps, including come-up, holding and cooling.
After retort processing, excess water on the packages is removed using a fan to dry the surfaces. The packages are then grouped into secondary packaging before being stacked on a pallet.
What are the benefits of carton packages for food products?
- The rectangular shape takes up 25-40% less space on the supermarket shelf than cans and glass jars.
- According to studies, consumers perceive cartons as a fresher package alternative.
- Cartons are significantly lighter than cans, resulting in efficient transportation. One truckload of Tetra Recart® cartons corresponds to approximately nine trucks delivering empty cans or glass jars. Once the packages are filled, a pallet will hold 20 percent more food compared with a pallet with cans.
- High quality printing on all sides creates opportunities for a billboard effect on the supermarket shelf
- Laser-perforated tear opening and simple re-closure make the package easy for consumers to handle.
- Tetra Recart carton packages are made of at least 69% renewable material (paperboard), while carbon emissions from Tetra Recart over the lifetime of the package are 81% lower than those of steel cans and glass jars. (Source:Life Cycle Assessment of food packaging, Europe 2017.)
Tetra Recart® carton packages
An innovative, future-proof packaging solution for shelf-stable foods, Tetra Recart® carton packages serves the evolving needs of consumers, producers, and retailers. Read more about our food carton packaging.
*Carton CO2 Calculator certified by the Carbon Trust.
** LCA report, 2020, European market