It's a gas, gas, gas!

It began life in the in 1930s with the use of carbon dioxide to store beef and lamb carcasses shipped to the UK from Australia and New Zealand. Yet the use of modified atmosphere packaging, or MAP, is still growing. And packaging firms and gas suppliers still innovate with new developments in packaging machinery and experiments with new gases and gas mixtures.

Today, as consumers turn away from frozen foods to fresh foods, the pressure is on for food processors to extend shelf-life. As a result, many items of fresh food -- from raw meat and fish and prepared fruit and veg, to ready-to-bake breads and pizzas -- now come bathed in their own inert atmosphere.

Fresh food can be packed in a protective atmosphere of pure carbon dioxide, nitrogen, or oxygen; a mixture of any or all of them; or even nothing at all. By excluding air; by actively suffocating bacteria; and by maintaining respiration in sealed fruit and veg packs, MAP gases can extend shelf-life up to five times longer.

However, there has been one big disappointment with MAP since Marks & Spencer first kick-started the MAP revolution in supermarkets by using oxygen to keep its fresh meat looking bright red. It has failed to make any serious inroad into the ready-meals sector. Despite all sorts of gas mixtures, including exotic and expensive ones such as argon, no one has come up with the perfect mixture that suits all the separate components that make up today's ready meals.

But there is still steady growth in MAP. Gas supplier Air Products has just updated its industry bible on MAP, A fresh approach to modified atmosphere packaging, first produced in 1995. And its food gases business, Freshline, has just teamed up with Glasgow food traceability firm Traceall to offer a web-based food traceability scheme.

Carbon monoxide challenge

Meanwhile, the European Parliament's refusal 18 months ago to permit carbon monoxide as a MAP gas (it's wonderful at maintaining the red colour of fresh meat and tuna fish) is being challenged. Meat processors across Europe, led by the Norwegians, hope to persuade MEPs that a tiny percentage of carbon monoxide will improve the look of fresh meat during the increasingly extended supply chain routes across Europe. Carbon monoxide is already a permitted additive in the US.

And confusion and controversy surrounds the use by some Asian and Thailand tuna fish exporters of labels declaring that packs contain 'tasteless smoke', 'clear smoke', 'cold smoke' or 'filtered smoke'. In effect they are all carbon monoxide. But since smoke is a permitted food additive, food safety authorities view these labels as an attempt to get round the ban on carbon monoxide.

So while MAP isn't exactly rocketing skywards, it clearly has a future. "There has been steady year-on-year growth in the UK as consumers move away from frozen foods to fresh foods," says Lisa Bishop, European marketing manager for food at gas supplier BOC. "And over the next five years I have no reason to believe the market won't continue to grow steadily."

Cylinders or bulk gases?

One consequence is a shift in the way food processors buy their MAP gases, says Michelle Jackson, business development manager for MAP at Air Products. "Someone new to MAP will start with cylinders of premixed gas. As their use of MAP grows, we find they tend to move straight to micro-bulk supplies of liquid gases, mixing them on site themselves." It is cheaper. It avoids cylinder handling. And because the micro-bulk containers are stored and topped up outside the food processing area, there are no hygiene problems, says Jackson.

But MAP gases are classed as food additives, and new European food traceability rules apply as much to the harmless nitrogen in a packet of crisps as they do to Sudan 1 dye. So in order to help customers with all their food traceability responsibilities, including MAP gases, Air Products has just introduced an on-line food traceability service.

The Freshline traceability and data management system enables remote, real-time data collected from anywhere in the supply chain, from fishing vessel or farm, to be transmitted by GSM satellite and mobile phone to the customer's desk. The data is compiled into tailor-made reports which can be integrated into a company's existing management systems. It will provide customers with everything they need to comply with the new legislation, wherever they are in the food supply chain, says Air Products.

Down on the factory floor, there are two approaches to MAP packaging. The simplest is to flush out the air in a food pack with the chosen MAP gas and then seal the pack. It is quick, it doesn't involve a vacuum, and it is relatively cheap. And it can be done on flow wrapping machines which offer great versatility with regards to changes in product size. However, residual oxygen levels can be relatively high, so reducing shelf-life.

The alternative is to use a vacuum to remove the air before flushing with the MAP gas. This gives much better control of residual oxygen. But it is slower. And the use of a vacuum requires the food to be placed in a rigid tray which can be sealed. This can be done with pre-formed trays on a tray sealer machine. Alternatively, thermoform-fill-seal machines are used which mould the trays, fill, and seal them in one operation.

Now, however, Swiss packaging company Ilapak has developed a vacuum version of its popular Delta 3000 horizontal flow wrapping MAP machine. This incorporates a novel vacuum flushing system to achieve residual oxygen levels comparable to conventional thermoform-fill-seal MAP machines. According to Richard Tearle, director of horizontal machinery for Ilapak in the UK, the machine is now completing field trials at a bakery customer in the UK. He expects to see the first production models on sale before the end of the year.

Vacuum flushing

"We can now evacuate a product and flush it with gas -- in this customer's case carbon dioxide -- before the product goes through the normal flow wrapping process. On this particular product we can get residual oxygen levels below 0.5% and up to six months' shelf-life. But normally we'd expect to extend shelf-life for bakery products by 50% or more." This will be particularly valuable in extending the life of partly baked products, says Tearle. Over recent years there have been steady improvements to the speed and efficiency of MAP packaging machinery, says Neil Ashton, sales manager of Packaging Automation in Knutsford, Cheshire. "We have seen a 50% increase in speeds. MAP is obviously still slightly slower than normal atmospheric sealing, but it is not the huge bottleneck it was."

When the European Parliament's Environment Committee narrowly voted in June 2003 to outlaw carbon monoxide as a food additive, it ended a 20-year tradition among Norway's meat producers of adding a tiny percentage of carbon monoxide (0.3-0.5%) to MAP gas mixtures. The aim was to preserve the fresh look of raw meat by forming a stable, cherry-red colour so that meat producers could transport and sell fresh meat in all parts of the country.

But MEPs were worried that the use of carbon monoxide to maintain the red colour would mask the normal visual signs of meat that had gone past its sell by date. They also ignored practice in the USA where carbon monoxide is on the Food and Drug Administration's 'generally recognised as safe' (GRAS) list of food additives.

Part of the problem was the association of carbon monoxide with "hosepipes and car exhausts", suggests Peter Scott, director of the British Meat Processing Association. But last May, the Norwegian meat industry announced it was teaming up with its European Union counterparts, including the BMPA, to get the ban on carbon dioxide lifted. "We would find carbon monoxide useful in the UK because of our enormously complex delivery system," says Scott.

To complicate matters, last August, the UK's Food Standards Agency warned about imports of fresh and previously frozen tuna that had been treated with carbon monoxide. And it also warned against 'smoked' tuna fillets containing significant amounts of carbon monoxide gas. In some cases, it said, the fish was not properly labelled to indicate the gas. And in others the description 'cold smoked' or 'lightly smoked' could be misleading, it said.

The FSA was echoing fears in Brussels that labelling such as 'clear smoke technology' was an indirect way of adding banned carbon monoxide. Yet in the US, the FDA happily permits foods labelled 'tasteless smoke', 'clear smoke', or 'filtered smoke'.

Air Products, tel: 01932 249200

BOC, tel: 01276 807594

BMPA, tel: 020 7329 0776

Ilapak, tel: 020 8797 2000

Packaging Automation, tel: 01565 755000