When things heat up: packaging for heat sterilization

The requirements that apply to packaging materials in the food industry are as varied as the products themselves. Some products have particularly high packaging requirements because they not only need to be protected, but must also remain shelf-stable for long periods of time, often without refrigeration. This impacts not only freshness, but primarily (food) safety: the purpose of such packaging is to prevent germs from growing.

This is where retort sterilisation comes into play. In this process, the packaged food is sterilized in a pressure boiler at high temperatures and while saturated with water vapor. This keeps the product shelf stable for months or even years – without the need for preservatives. However, for this process to work the packaging materials need to withstand these extreme conditions without losing their protective function.

The solution? Retort barrier packaging – a specially developed packaging solution created precisely to meet these requirements.

Retort barrier packaging is an innovative solution for foods that must withstand thermal sterilization. They have been specially developed to handle high temperatures in retorts – while reliably protecting against oxygen, moisture, and light. This barrier is essential to ensure the long-term quality of sensitive products: the taste, color and nutrients are retained, while oxidation – one of the greatest enemies of shelf-stable foods – is effectively prevented.

Another key advantage, is that products in such packaging require no refrigeration, and offer consistent, long shelf lives. This makes storage and distribution significantly simpler – and ensures reliable freshness whenever it is needed.

In comparison to traditional containers like cans or glass packaging materials, there is another practical and economic benefit: retort barrier packaging made of plastic is lighter, and results in lower material and transportation costs. Thanks to this combination of efficiency, functional protection and comfort, it is a state-of-the-art answer to the demands placed on modern food packaging.

Retort barrier packaging is based on a seven-layer foil structure specially developed to meet the requirements of the retort process. The outer layer is generally made of polypropylene (PP), which is known for its flexibility and stability.

This layer protects the product against outer mechanical influences and ensures that the packaging remains intact during the entire process. Inside this, there is a layer of recycled polypropylene. This not only helps improve packaging durability, but also helps make the entire manufacturing process more environmentally-friendly.

The central barrier layer made of ethylene-vinyl-alcohol (EVOH) plays a key role. EVOH provides outstanding protection against oxygen and moisture, thereby preventing oxidation and the loss of taste and nutrients. This layer ensures the packaged product retains its original quality even after a long period of storage. It also protects against the growth of microorganisms that could impact food safety.

The other layers of the packaging are used for adhesion and stability, so that the different material layers remain reliably bonded.

Greiner Packaging offers its customers the choice between symmetrical and asymmetrical foil structures. 

Symmetrical structures are characterized by individual material layers of the same thickness. This even distribution gives the packaging a stable form, while allowing it to consistently serve its function as a barrier. One unique characteristic of this structure is the use of additives in the central EVOH layer. They improve the barrier properties of the EVOH layer at high temperatures, helping the layer to remain stable during the retort process and preventing oxygen exchange. This is key to extending the product’s shelf life.

Thanks to the even distribution of layers, the packaging can be thinner, thereby making material usage more efficient and reducing production costs. This structure is also advantageous from a sustainability standpoint, since the small percentage of EVOH has little impact on the recycling process, thereby improving recyclability.

The asymmetrical structure also serves as an outstanding barrier for retort sterilization; this is achieved through a varied distribution of layer thicknesses. The inner PP layers, which are closer to the food, are thicker than the outer ones. This optimally protects the EVOH barrier against temperatures and moisture. One advantage of this structure is the flexibility in constructing the EVOH layer: depending on the use of additives, it can be made thicker, the same thickness, or even thinner than in the symmetrical version. This allows the use of additives to be reduced or even eliminated altogether, depending on product requirements and customer needs. This can further enhance the sustainability of the packaging.

Both types of structures have their own advantages, as well as unique challenges. Using additives in the EVOH layer can offer functional advantages, but can also negatively impact recyclability and change coloration – an issue for brand-specific designs. The additive-free alternative, in contrast, requires thicker inner layers. This increases material consumption. One thing is clear: neither solution is entirely superior to the other. Instead, what is most important is developing flexible concepts that can be tailored precisely to specific product requirements.

Greiner Packaging offers a wide range of production technologies for multi-layer, rigid barrier packaging – each of them carefully designed to meet the diverse requirements of modern packaging solutions. The so-called inline process is one particularly pioneering method which stands out not only for its efficiency but also for its remarkable flexibility. The inline process facilitates efficient, cost-saving production since all steps – from extrusion to forming and processing – are connected directly in a continuous production line. This approach minimizes conversion times and ensures rapid production, saving time and resources. In addition, the inline process offers high flexibility in packaging design, in particular in adjusting the thicknesses of all layers to optimally coordinate the packaging to applicable product requirements.

Another advantage of the inline process is reduced material waste. Residual materials during production can be reused immediately and integrated into the materials cycle. This makes production more environmentally-friendly by minimizing waste and ensuring resources are used efficiently. Quick and continuous production also increases capacity and results in a faster time-to-market, giving companies a competitive advantage. Thanks to this efficiency and flexibility, the inline process is a cost-effective and sustainable solution for manufacturing retort barrier packaging.

High-quality wet pet food places high demands on packaging materials. Pet owners expect food to not only remain fresh and safe, but to also be packaged in an environmentally-friendly manner. Retort barrier packaging is excellent at meeting all of these expectations by extending the shelf life of the wet food – without the need for artificial preservatives. The food remains fresh over long periods without changing its taste, simplifying both storage and transportation. In addition, this packaging offers a sustainable solution and helps reduce food waste. Since less frequent deliveries are required, and since packaging materials can be recycled efficiently, they are also good for the environment.

Retort barrier packaging is also a suitable solution for ready-to-cook meals. Consumers want products that are not only fast and practical, but also safe and high-quality. This packaging keeps ready-to-cook meals shelf-stable for longer without the need for preservatives, while the taste of and nutrients in the product are preserved. Thanks to the packaging’s high temperature-resistance, ready-to-eat meals remain safe even after sterilization or pasteurization, and retain their original quality. In addition, this packaging solution helps reduce the CO₂ footprint of the product.

For products like infant and toddler foods and medical nutrition, which are often used to care for older persons or persons dependent on that special care, retort barrier packaging is an ideal solution. It reliably protects these sensitive foods against external influences that could negatively impact their quality and nutrient composition. Protection against oxygen and moisture, which could destroy valuable nutrients, is particularly essential. Thanks to this specialized packaging, the nutrient content remains stable even during long storage or transportation terms, ensuring consistent product quality.