The barrier calculator is a useful tool for different geometries like film, cup, bottle and cuboid. It enables you to simulate your target package design.

The main idea of food packaging is to contain and protect the food through the distribution and retail chain to the consumer. The time a product can remain fresh for consumption is its “shelf life” and this article discuss how this is influenced and how you can simulate this.

Food are produced or prepared and packed in many different ways. The food can be:

• Fresh meat, poultry, fish
• Cooked, cured, dry, salted
• Fresh vegetables
• Dry flour, rice or pasta
• Prepared foods, ready meals
• Liquid juice, milk and beverages

In this article we will look specifically on plastics barrier packaging and how to estimate the shelf life by simulation.

Shelf life

A good definition of shelf life is: “The period between the manufacture and the retail purchase of food product, during which time the product is of satisfactory quality in terms of nutritional value, flavour, texture, appearance and safety.”

Obviously, the shelf life of a packed product will have a complex dependency of several factors such as:

• The products nature and “activity”
• The environment in the distribution chain and especially temperature
• The properties of the package and especially its permeability

The way a product deteriorate is also many including: microbiological and/or enzymatic deterioration (aerobe and anaerobe), oxidation e.g. Lipidic oxidation of fish or Rancidification of fatty foods, moistening, drying and other changes in taste, odour or colour.

A key aspect of the package is its barrier against gas permeation and how well it can maintain a specific inner atmosphere with concentrations of O2, H2O, CO2, N2. In particular, we will look at examples of meat products where oxygen permeability is of high importance and cereal products where moisture permeability is the key.

Permeability

Plastics seems impermeable but that is not correct. Conventional packaging polymers such as PET, PE or PP have a rather high permeability for O2 and give limited protection while for moisture they give a good protection. Some other polymers like PA and EVOH on the other hand have high barrier against O2 and protects food well. These different materials can be combined in order to obtain the right performance - like in below figure.

Simulation

Norner has developed a web based calculation tool for oxygen transmission rate (OTR) and water vapour transmission rate (WVTR). The calculator is available at www.barrier.norner.no. It allows the user to specify:

Various package types

• The package dimensions
• The type and thickness of different polymers in the wall of the pack
• The (storage) temperature and relative humidity
• The time for which permeation shall be calculated.

Benefits

The calculator is easy to use and flexible in how you can specify the package and conditions which allows:

• Storage/transport condition can be specified and varied
• You can use it to generate data for your packaging system as a basis for correlation curves
• When you know the product tolerances, shelf life can be estimated
• Virtual testing of various package types and layer constructions
• Compare performance of structures to their anticipated costs 

Examples of calculation and simulation

OTR of Vacuum packaged red meat

Meat has a natural high activity and is affected by the presence of oxygen, which may lead to microbiological activity and turn the meat bad.

We shall calculate the shelf life of a piece of beef in a vacuum pack. The packaging film is a 7 later PE/PA/EVOH structure.

The input data for the calculation is:

The following 7-layer structure:

• 40μm PE / 4μm Tie / 5μm PA6 / 3μm EVOH32 / 5μm PA6 / 4μm Tie / 40μmPE
• Film surface area 25x40cm2
• Relative humidity 65%

We calculate the O2 ingress at different times and storage temperature and plot the results as shown to the right. We specify the O2 limit to 1ml

Conclusions

Under the specified conditions:

• The shelf life is >60 days at 2°C
• At 10°C the shelf life is only half

Similar calculations can be made for alternative packages.

WVTR of a pouch for cereals

Cereals are dry and with a very low activity. Their shelf life will naturally be long but a critical issue is moisture ingress by which they may turn soft.

We shall calculate the shelf life of cereals in a PE pouch.

The input data for the calculation is:

• The following 3-layer structure: 10μm HDPE / 10μm HDPE / 10μm LDPE
• Film surface area 30x50cm2
• Temperature 20°C
• Relative humidity inside 0%

We calculate the H2O ingress at different relative humidity in the storage and plot the results as shown to the right. We specify the H2O limit to 15g

Conclusions

Under the specified conditions:

• The shelf life is 700 days at 20% RH
• At 50% the shelf life is only half

Similar calculations can be made for alternative structures or thickness.

You can find more information at Norner Barrier Calculator.