Equipment

Modified atmosphere packaging may have been around for 20 years, but some sectors of the food industry have yet to be persuaded of its value.

It’s easy to see why MAP has caught on throughout the UK food industry since it was introduced 20 years ago as a way to prevent red meat from turning brown.

The technology, which slows or halts the growth of bacteria and can prolong shelf life and increase the attractiveness of products, is now indispensable for producers in sectors ranging from salads and meat to pizza and cheese.

Some areas of the food industry have, however, been a little slow on the uptake. Take poultry for example. While their red meat counterparts are practically MAP veterans, poultry producers and packers have only submitted to MAP in the last three years. Even then it was only because they realised that packing chicken portions in polystyrene trays over-wrapped with clingfilm wasn’t the best way to avoid contamination, prompting an industry-wide shift to MAP.

However, there are still parts of the food industry that are relatively MAP-free zones, such as the ready meals sector, where the composite nature of the product often precludes its use, says Craig Holmes, sales manager with gas analysis equipment company Systech Instruments. “Because ready meals are often a complicated mixture of ingredients, many of which require different gas atmospheres to prolong their shelf-life, getting the right gas mixture can be impossible.”

Other barriers
There are barriers to the use of MAP in other applications too, though equipment manufacturers are working to overcome some of these issues.

For example, meat and fish products often contain residual liquid which doesn’t look particularly attractive when sliding around in a tray. Multivac, a manufacturer of thermoformers, tray sealers and vacuum packers, believes its skin packaging technology offers the solution to this problem. “We use a permeable draping material to hold the product in place,”says Jim Campbell, general sales manager (thermoforming and tray sealing). “Then we have a top web that we seal to the tray and we can gas into that middle layer, as the gas will permeate the skin material. So you get the dual benefit of the product being held in place and the shelf-life being prolonged.”

Residual oxygen can be another potential deterrent to the use of MAP. If the oxygen content in cooked, sliced meats is too high, for example, a green shimmering effect will form on the surface of the meat, which, although perfectly safe, is off-putting for consumers. Multivac has developed a machine capable of achieving ultra-low oxygen levels (0.02%) through double evacuation and flushing.

The ability to guarantee seal integrity is perhaps the single most critical factor to success for the manufacturers of MAP packaging machinery, as a leaky seal will completely nullify all of MAP’s advantages.

Campbell says three factors – sealing temperature, pressure and time – affect seal integrity. On Multivac’s machines a constant sealing temperature is maintained with a water cooling system and high pressure applied through the sealing dies. The machines are also microprocessor controlled, giving tight control over the sealing operation.

The company has also developed its Twinseal “belt and braces” system for MAP packs. Instead of forming one seal around the outer edge of the pack, it forms two narrower seals that allow for greater pressure. “If you were packing a salad and a piece of lettuce strayed into the seal area, if the first seal didn’t catch it, the second seal would,” says Campbell.

Although in its infancy, radio frequency technology has been touted as one potential solution to seal integrity issues. It can seal through contaminants such as fat, oil and sauce, eliminating the problem of leaking packs. Heat sealing equipment manufacturer Proseal is developing a tray sealer which incorporates the technology.

Rose Forgrove says its Integra HS system has the edge over other flow-wrappers in seal integrity because the sealing time and temperature are not affected by changes in speed. “On most MAP machines, sealing time is proportional to the machine’s speed,” says Steve Moore, sales manager UK south and export. “To compensate for that, historically you had to adjust the sealing temperature, but it takes a while for the temperature to change. On our machine, the sealing time remains the same regardless of the machine speed.”

Keeping up with production
If speed was ever an issue with MAP packaging machines, it doesn’t appear to be anymore.
The Integra HS is capable of processing up to 200 packs per minute, almost double that of its predecessor. “We’ve achieved it by reducing the machine’s size capability, so maximum pack width is 270mm rather than 400mm, and we’ve cut the weight of the moving parts by 50% so they move faster,” says Moore.

Proseal, meanwhile, has taken another route to increased speed with the ‘free flow’ gas purging system on its tray sealers. The system doesn’t require a vacuum to be pulled, reducing the cycle time as well as tooling costs while still achieving good residual gas levels.

Ishida Europe says the increased production speeds demanded by the industry have led it to develop a high capacity MAP tray sealer, the QX-1100, which combines quick changeover with quality control features such as checkweighing, gas mixing, product coding and gas analysing. The QX-1100 is capable of sealing 200 trays per minute.

Ultimately, though, as with any technology, the capital outlay for equipment and the running costs can deter some manufacturers from investing in MAP. However, technological advancements are making it cheaper to adopt.

Closed loop gas injection technology from gas analysis equipment companies such as Witt Gas can save users money by analysing and controlling the residual oxygen in the pack as it is being flow-wrapped.
“After the gas flushing lance fills the pack with gas, an analysis tube measures the amount of oxygen around the pack prior to the second seal being made and controls it to a set point,” says Carl Long, general manager with Witt. “Without such a system people often use more gas than they need to.”

Generating nitrogen on-site rather than buying cylinders is another way to reduce the ongoing costs of MAP. Domnick Hunter has just upgraded its Maxigas nitrogen generator (pictured), incorporating equalisation technology and a user-friendly interface into the system. Equalisation works by capturing and recycling some of the exhaust gas, reducing the amount of air needed to drive the generator.

“Equalisation technology gives two benefits: it allows us to get more nitrogen out of the generator and use less air to drive it,” says Bill Zorlutuna, the company’s market sector manager. “Because you need less air, your compressor can be smaller, saving on energy costs. So you get more bang for your buck.”
Another way of easing the investment burden is to try before you buy. This is what Irish poultry producer Oaktree Foods did when it was launching a new line of chicken burgers for Marks & Spencer. In case the launch didn’t go to plan, it leased a MAP heat sealing machine from Packaging Automation.

“We weren’t sure if the range would be a success, which is why the hire option was so appealing to us in the first instance – it allowed us to market a new line without the financial risk,” says Brian Turkington, maintenance manager at Oaktree.

Packaging Automation says the PA2016 MAP-V is one of the most popular machines in its hire fleet. Oaktree uses the machine to pack fresh produce in vacuum format, and switches to atmospheric for frozen products.


Feeling flush
With the major retailers increasingly specifying MAP, snack manufacturer Largo Foods decided to invest in gas flushing equipment for its Ashbourne plant in County Meath, Ireland.

It ruled out gas cylinders on the basis of cost as well as health and safety; the high-pressure cylinders would have needed to be stored and handled. Instead the company turned to Dalco Nitrogen Systems, exclusive distributor of Domnick Hunter Maxigas gas generators.

The Maxigas system generates nitrogen from compressed air by using the pressure swing absorption principle to separate nitrogen molecules from the air stream.

Largo’s customers have strict quality controls, typically demanding a residual oxygen content of less than 4%, so nitrogen reliability was crucial. Dalco installed a dual bank N2MAX116 and 110 to produce nitrogen gas at a purity of 99% – well within Largo’s specification. Gas is flushed into hoppers that are attached to form-fill-seal packaging machines just before sealing.

Tony Gallagher, maintenance manager at Largo, says: “When we investigated the costs of bulk cylinder supplies, it just wasn’t viable; they were 10 times more expensive than gas from Maxigas.”