Advanced Retort Packaging Solutions for Food

Posted on Jul 17, 2025 in Technology

Plastic Retort Containers

Retort packaging encompasses various forms designed for sterilization, including:

  • Flexible retort pouches
  • Rolled Aluminum/PE trays
  • Semi-rigid trays
  • Thermoformed trays with lids
  • Tubs with double-locking metal lids
  • Complex cardboard boxes

Flexible Retort Pouch Characteristics

Compared to conventional packaging, flexible retort pouches offer distinct advantages due to their flat cross-section and reduced product thickness:

  • Rapid heat transfer, leading to reduced sterilization time.
  • Improved food quality with less thermal damage to retail packaging.
  • Ability to integrate package formation and filling (saving storage space for empties).
  • Reduced weight and space for transport and storage.
  • Easy opening feature.

Barrier Packaging Materials Explained

While metallic materials and glass provide almost complete barrier properties, plastic materials exhibit varying barrier capabilities, generally not matching metal or glass. Most conventional plastics offer an adequate water barrier for many applications. However, very few provide a high oxygen barrier. A plastic material is considered high-barrier if its oxygen permeability (PO2) is less than 10 cc/m2.day.atm.

High-Barrier Plastic Materials

Simple Polymeric Materials
  • PVDC (Polyvinylidene Chloride)
  • EVOH (Ethylene-Vinyl Alcohol Copolymer) and PVOH (Polyvinyl Alcohol)
  • Certain Nylon compositions
  • Polyketones
  • Polyacrylonitrile
Complex Barrier Structures
  • Laminates with Aluminum (Al)
  • Plastics metallized with Aluminum (Al)
  • SiOxy (Silicon Oxide) and Alox (Aluminum Oxide) coatings
  • Plastics incorporating nanoparticles (e.g., functionalized clays)
  • Multilayer plastic structures

Ethylene-Vinyl Alcohol Copolymer (EVOH)

The polyvinyl alcohol (PVOH) homopolymer is an excellent polymeric barrier to permanent gases. However, it is challenging to process and is water-soluble and moisture-sensitive. Therefore, hydrolyzed ethylene-vinyl alcohol copolymers (obtained from EVA hydrolysis) are commonly used. These copolymers are marketed with varying ethylene percentages, typically 29%, 32%, 38%, 44%, and 48%. The material properties are a function of the alcohol percentage. Compared to PVdC, EVOH copolymers are easier to process by extrusion, are less dense, and do not pose the same environmental impacts during incineration.

Disadvantages of Flexible Retort Pouches

  • Low operating speed of packaging lines (60-120 units/min).
  • Requires strict sterilization control (e.g., backpressure steam-air mixtures).
  • Requires individual handling of filled containers during sterilization and packaging transport.
  • Limitation of available formats.
  • High investment for installing new lines.
  • Need for over-packaging for commercial handling.
  • Shorter product shelf life compared to products packaged in metal or glass.

Sterilizable Trays and Tubs

The development of sterilizable trays and tubs began in the 1970s as an alternative to retort pouches.

Lamipack: Early Retort Tray Example

Lamipack was one of the first examples developed by Japanese manufacturers. It consisted of a multilayer structure of PP/PVDC/PP. Subsequently, PVDC was replaced by EVOH. These containers can be sterilized up to 135°C, providing an excellent barrier to gases and ensuring food stability for at least one year of storage at room temperature.

Sterile Thermoformed Trays

These are flat trays thermoformed from high-barrier multilayer material with a heat-sealed flexible lid.

Key Requirements for Sterile Trays

  • Sterilization temperature tolerance: 121-135°C.
  • Tight seal against microorganisms and gases.
  • Low oxygen permeability.
  • Low moisture permeability.
  • Possibility of multi-chamber designs.
  • Microwave/convection oven compatibility.
  • Heat-seal closure traction resistance > 25N/25mm.

Tetra Recart Packaging System

The Tetra Recart system is composed of six layers and can withstand temperatures of 128°C, humidity, and pressure for two hours.

Tetra Recart Laminate Structure

The Tetra Recart laminate typically includes:

  • Fibrous cardboard
  • Two adhesive layers
  • An aluminum layer
  • Patented ink with a peel-strength lacquer coating
  • A polypropylene layer