New to Gas Flushing

New to Gas FlushingWhat is Modified Atmosphere Packaging?

Why Use It?

MAP – Modified Atmosphere Packaging – is a packaging method where the gas surrounding the packed food product is exchanged for a single gas, or another mixture of gasses. In Europe the MAP gasses almost exclusively used are those that we normally breathe in the atmosphere, nitrogen (N2), oxygen (O2) and carbon dioxide (CO2).  Normal atmospheric air contains 78% nitrogen, 20.9% oxygen, 0.9% argon, 0.04% carbon dioxide.

Transport & Extended Shelf LifeThe primary purpose of using MAP is to extend the shelf life of the product being packed, giving more time for it to pass through the distribution chain and be safely consumed. MAP is commonly used in conjunction with storage at lower temperatures.

“ Gas packing” was first used in the 1930’s for the bulk transport of meat from Australia & New Zealand to the UK. and in the 1940’s & 1950’s similar controlled atmospheres were used for storing fruit. It was in UK & Denmark during the 1970’s that MAP started to be used in retail packs, a process that has now been adopted around the world.

Benefits in Food Presentation – In addition to maintaining product shelf life and reducing health hazards related to food, MAP has the huge presentation advantage over other packaging methods because it helps to maintain the natural colour of the food and thereby it’s appeal to the consumer. Other benefits are as an alternative to using artificial preservatives, reduces product & packaging waste because the product has a long time in which it can be consumed and also enables users to sell their product into markets that are more remote from the point of production.

Dansensor MAP Quality Control for SaladWhat Does Each MAP Gas Do?

Nitrogen (N2)  – an inert gas with two principal MAP functions.

  1. As a replacement for air, and primarily to exclude oxygen.
  2. As a filler gas – nitrogen is not soluble. Carbon dioxide for example is both water & fat soluble and it’s use can cause packs to deflate.

Carbon Dioxide (CO2) – has the primary MAP function of inhibiting the growth of aerobic bacteria. However, because of the solubility of carbon dioxide in water & fat, packs collapse from a reduction in internal pressure as the gas dissolves, and a slight tainting of the product may result.

Oxygen (O2) – usually, oxygen is excluded in MAP packaging, because it causes oxidative deterioration of foods. However, it maybe used as an MAP gas to:

  1. Inhibit anaerobic organism growth
  2. Allow respiration to occur (important for fruit & vegetables)
  3. Maintain colour (particularly in red meats)

Which Gas Mix Should Be Used?

A general guide is shown below, but expert advice should be obtained to ensure that the most appropriate gas mix is used for packing each specific product.  We recommend speaking to the MAP specialist at a gas supply company, or at the Food Research Company. Those offering advice include:

Dansensor MAP & Flow Wrap MachinesWhy Are The Packaging Materials Used So Important?

Different types of materials have different properties. The most commonly used formats for packaging materials include types of tray and /or film. The most important properties include:

  1. Barrier to gas & water vapour transmission. The barrier properties, as measured by their permeation rates, have to be sufficient to ensure that the environment within the pack is maintained within the required limits for a period exceeding the shelf life of the product.
  2. Sealability is critical to maintaining the internal environment within the pack. An hermetical seal must be formed to ensure that the MAP gas remains in the pack and does not leak out. Different films have different sealing characteristics and so should be chosen with care, taking into consideration packaging line speed & dwell time of the film in the sealing jaws.
  3. Thermoformability. Important if a thermoformer packaging format is being used. The film must be able to withstand being heated & deformed to make a pouch while maintaining the integrity of it’s barrier.
  4. Transparency. As visual presentation is one of the advantages of using MAP, anti-mist coatings can be applied to prevent unsightly water droplets forming and detracting for the product’s appearance. Care should used, as excessive quantities of anti-mist coating can affect the sealability of the film.

Specialist advice can be obtained from packaging film suppliers including:

What Types of MAP Packaging Machine Are There?

The four most common types of packaging machines used in Modified Atmosphere Packaging are:

1. Tray Sealing – The food product is placed in a pre-made rigid tray and the air within the tray is either vacuumed out & then the tray is either:

  1. flushed with the modified gas and film is top sealed on the tray
  2. simply flushed with modified gas to push the atmosphere out and top sealed with a film.

Tray Sealing machines are available in a range of sizes from small manually operated to fully automated twin lines. Tray seal packaging machine suppliers include:

Sealpac A6 Machine in Action

Sealpac A6 Machine

2. Thermoform-fill-seal (TFFS ) – This is a stage process, where the thermo-deformable thicker base web is unwound, heated and drawn into a set of dies to form a series of pockets. The product is placed into the pockets. The filled pockets are then moved to the second stage station where the atmosphere is evacuated from the pockets and the MAP gas is flushed into the pockets, which are then sealed with top film. The outer edge of the packages are then cut free from the base web. Thermoform package machine suppliers include:

Sealpac RE30 Thermoformer in action

Sealpac RE30 Thermoformer

3 – Horizontal form-fill-seal ( HFFS ) – or more commonly known as Flow Wrapping machines. A single film
web is fed horizontally and formed into a travelling “tube” of film. The film tube is sealed  along it’s back (fin) seal
and over wraps the individual products. The MAP gas is flush into this tube, pushing the air back out of the tube,
which is then sealed in front of and behind the product to form gas flushed individual packs. Flow wrap machine suppliers include:

Horizontal Flow Wrap

PFM Horizontal Flow Wrap

4 – Vertical form-fill—seal ( VFFS ) – commonly known as ‘Baggers’, this is where a single film web is fed vertically around the outside of a forming tube and is sealed vertically to form a tube of film. Product is dropped down the inside of the forming tube, coming to rest on the bottom seal of the tube, which has already formed when the top seal of the preceding bag was made. The tube is either continuously, or pulse flushed, with MAP gas to expel the atmospheric air and then the top seal is made, producing a hermetical sealed package with a protective atmosphere inside. Bagging machine suppliers include:

Vegatronic 4000

Ilapak Vegatronic 4000

Dansensor MAP Gas FlowHow Do I Deliver Mixed Gas To The Packaging Line?

The 3 principle options for delivering mixed gas to the packaging lines:

1 – Pre-mixed gas bought from the gas company – this option is useful and cost effective, when using small quantities of gas. It avoids the need to buy separate gas storage for each gas being used and also avoids having to buy a gas mixer to do the mixing. However, the cost per litre is expensive and so it is not economic when using anything but small quantities.

2 – Master gas mixer & buffer tank – this requires having a sufficiently large gas mixing capacity feeding a buffer tank, which then feeds a number of individual packaging lines. This method requires that all packaging lines always use exactly the same gas mix. It has the advantage of avoiding the need to purchase and maintain a gas mixer for each packaging line, but reduces plant flexibility and runs the risk of shutting down all of the lines in the event of a failure, with no spare being available.