The role of gases such as liquid nitrogen and CO2 in the food processing sector is imperative to the quick, economical and high-quality delivery of food products to supermarkets and our households, as Rob Cockerill finds out.

Believe it or not, the industrial gases industry plays a significant and economically beneficial role in almost every aspect of our everyday lives.

While the many applications in the metallurgical, medical and semiconductor industry’s among others are perhaps those that spring to mind first and foremost, the role of industrial gases in the food processing sector is equally noteworthy.

Uses in the chilling, freezing and packaging of fresh, cooked and prepared foods are essential and far more important than many may be aware of. There are also the uses for alcoholic and
non-alcoholic beverages and freeze-dried products such as coffee or gravy granules.

Food processing
Food preservation has become an important and growing need across all sectors. Industrial gases have a strong association with fresh food, cooked or prepared food and frozen goods. All three of these aspects have been users or consumers of industrial gases and this is likely to continue long into the future yet.

Chilling applies to a whole variety of fresh foods including meats, cheese, fish and other prepared foods, with the aim of trying to keep food fresh at around 4oC and extend its shelf-life without freezing the produce.

Cook-chill methods are quite self-explanatory and involve cooked, prepared and hot foods which are then left to cool gradually and chilled much later. At least that’s how the old process used to work, the new process now taking the hot food and chilling it straight away to between 0oC and 4oC ideally, using either mechanical refrigeration or gaseous techniques.

In the case of freezing, this could include anything from peas and prawns to burgers and pizzas and could also use either mechanical or cryogenic (gases) refrigeration. The aim is invariably the same, whether cooked or prepared food: to get the product down to -18oC as soon as possible and therefore retain as much of the quality as possible. This is most commonly achieved through the mechanical refrigeration method, though the cryogenic technique of Individually Quick Frozen (IQF) or ‘Crust Frozen’ is something of an instant, optimum answer and also maintains the high food quality as it does not allow large ice crystals to form in cells.

Naturally, different foods require different processing methods and gases but cryogenic forms of freezing and refrigeration may be the most obvious choice, depending on the use.

While this may be a somewhat expensive method to operate on the basis of ongoing running costs, the freezing properties of liquid nitrogen for example at -196oC are instantly advantageous. A similarly fast process, using the direct effect of CO2 at -80oC and injecting dry ice ‘snow’ on to the food is just as cheap and effective. Rather than generating the cold as in mechanical refrigeration processing (using significant power and requiring large factory space), the cold is in the gas!

It is not just in the freezing or chilling of foodstuffs that gases are active participants. There is also a fundamental role to be played in the actual delivery of the product, as almost every single food item requires packaging.

Modified Atmospheric Packaging (MAP) is a rapidly growing method with what appears to be a strong future in the food industry. Modifying the air composition surrounding the food item, the level of oxygen is reduced and deterioration vastly slowed down, extending the shelf-life.

Emma Guthrie, European marketing manager of food and industrial cryogenics for Air Products, notes that the technology is already well established and a promising future ahead is likely.
“MAP has become one of the most successful ways of packaging and an effective way of increasing the shelf life of many food products, both chilled and ambient. It is well established in a lot of European countries like the UK and Ireland, France, Germany and Spain. For emerging nations like Poland, the Czech Republic and Portugal, the future of MAP is looking very bright as lessons learned from machinery and packaging film suppliers are used,” Guthrie comments.

MAP is an innovative technique for prolonging the shelf-life period of various types of products, predominantly fresh or minimally processed foods and maintains or extends the initial fresh state of the product.
Simply a practice of alteration to the internal atmosphere of packaged goods, a food item is placed in a container or the desired packaging and surrounded by a gas mixture much lower in oxygen to the air we breathe, and then sealed. Nitrogen accounts for 78% of the air and oxygen around 20% and in the process of MAP, it is the target to reduce this oxygen from 20% to as low as 0%. This significant reduction of oxygen means that the Aerobic bacteria, which thrive on oxygen and damage foods, cannot survive and little or no deterioration can take place.
The most common gas mixtures for these packaging requirements tend to involve CO2, as this is an acidic gas and an effective bacterial inhibitor, though nitrogen and a nitrogen and CO2 combination are also widely used.

High CO2 levels are extremely effective in the packaging of meat, fish and other similar fresh produce. This ratio of gases is also effective for reducing respiration and ethylene production rates in fruit and vegetables, therefore delaying the ripening process. However, low levels of oxygen (3-5%) are still essential when packaging fresh fruit and vegetables, as the absence of oxygen can lead to Anaerobic respiration in the package and the acceleration of senescence and spoilage.

In many instances, the removed oxygen in an atmospheric gas mixture can be replaced by nitrogen as this is commonly acknowledged as an inert gas. Used as something of a filler gas, nitrogen neither encourages nor discourages bacterial growth and is present in most packaged products.

Cryogenic or mechanical?
While MAP techniques are fundamental to the actual delivery and storage of food items and would appear to have an increasingly bright future ahead, the role of industrial gases in the chilling and freezing aspect of the food industry is not so clear.

We’ve already established how integral industrial gases are to the methods of refrigeration, but it is which method is likely to figure prominently in the years to come that is the question.

In light of rising gases costs and distribution expenses, it is suggested that preferences are switching back towards mechanical refrigeration and it is this which raises doubts about the direct involvement of industrial gases in the future. The investment costs and initial outlay for mechanical refrigeration may be much more expensive, but the regular running and operation costs of liquid nitrogen (LIN) and other such gases work out similarly expensive and if anything, are increasing in price.

So what is the current trend in the industry?
Increased costs of using cryogenic refrigeration and the technical improvements of mechanical refrigeration are important factors in determining which of these methods is favourable at any given period.

A company well-placed to assess these technical improvements and the current trend in refrigeration, is Belgium-based Cryogenic Equipment & Services (CES). CES is the major independent supplier of cryogenic equipment for the food, metal and pharmaceutical industry and a respected world leader in the design, engineering and manufacture of cryogenic and mechanical chilling and freezing equipment.
Hans Vanackere, director of CES, believes that although cryogenic refrigeration has its many merits, the preference at present is moving towards mechanical refrigeration.
The current trend is mechanical refrigeration. There are miscellaneous reasons we could mention. Cryogenic refrigeration is always superior and quicker, but mechanical refrigeration has made a lot of progress and for companies operating at a larger scale due to mergers and fusions, mechanical refrigeration is more advantageous,” Vanackere explained.

A modern day tendency to rely on pre-cooked, chilled foods is also seen as a contributory factor in favour of mechanical methods. Vanackere comments, “For a tendency for ready-to-eat meals that are not frozen but fresh, where only cooling is needed and not freezing, again it is better to use mechanical.”

This trend towards mechanical refrigeration is also consistent in the US, where this method of food processing would seem to be the dominant option across the board for a number of reasons.
“In the US and Canada, mechanical refrigeration represents about 90% of the market and cryogenic refrigeration rounds out the other 10%,” comments Phil Davis, communications manager for North American Industrial Gases Division of , Praxair Inc.

“Many factors determine the selection in type of refrigeration that a company makes. These include production rate, cleanability, yield, capital investment, local utility rates and space consideration. The value of the product can also determine the type of refrigeration selected, including the expected post-freeze or post-chill condition of the product.”

Approximately 8% of Praxair’s total industrial gas business is attributed to food and beverage and the company also manufactures its own line of cryogenic freezers, chillers, and vessel and piping systems to serve the entire needs of its food customers. From the company’s position and perspective, it seems that mechanical is indeed popular at present and the customers’ choice, though changes in circumstance and environment can sway trends.
Davis comments, “The mechanical system is an easier sale due in part to the market position, existing equipment in use and traditional processing. As new products are developed or customer expectations change, so must the way frozen and refrigerated foods are produced.”

In contrast, Derrick Norvill, head of food treatment at Linde Gas, believes there is an increase in both methods of refrigeration and concurs that any preference is purely regional. If anything, it is suggested that cryogenic refrigeration is in fact on the increase. “We have seen a general upturn in demand for refrigeration systems across all geographies, both for mechanical and cryogenic,” comments Norvill.

“Current trends vary from region to region and depend on factors such as government subsidies, cost and reliability of power and type of product to be chilled or frozen. We are seeing a growing demand for cryogenic systems as they can be delivered and installed more quickly than mechanical. I am convinced that cryogenic food freezing and cooling will have a major part to play in the industry for many years to come but it is also important for the gas companies to be innovative and creative in developing new applications and systems.”

Air products, a global provider of industrial gases, has been working closely with the food industry since 1965, and seems to agree with this view, as Emma Guthrie says, “The trend is for both. We at Air Products are always looking to support applications where the customer can achieve a value with the cryogenic solution. This can be seen with our range of cryogenic tunnel freezers, which include tunnels designed for stand-alone use or for integration into processing equipment.”

“Additionally, Air Products is always looking to develop innovative solutions that can bring value to the food processing market. These include cryogenic coating and mixing systems and most recently a sauce chiller that can rapidly chill sauces and mayonnaise products using the power of liquid nitrogen,” Guthrie adds.

The size and scale of a company and its operations are also likely to be influential in deciding which method is best suited to the application, as any new enterprises are likely to opt for cryogenic refrigeration due to its lesser initial investment costs. This is reinforced by Vanackere as he says, “For start-up companies in the food industry, the capital outlay (of cryogenic refrigeration) is a lot lower.”

Industrial gases in the future
The current dynamics of the food processing industry and global economic position had seemed to suggest an emerging preference for mechanical refrigeration, but on reflection it appears that cryogenic methods are still bringing home the bacon too.

Trends, like fashion, can change very quickly and the role of industrial gases in the long term should not be ruled out. Vanackere reassures as he comments,
“Industrial gases will always be used in the food industry for the following reasons: it is a superior way of freezing and chilling with a better quality final product; it is more flexible than mechanical freezing and you can start right away; certain food products can only be frozen cryogenically; and for companies with a lack of space, this can be the solution.”

And this view is supported by Messer’s Lammertz as she says, “Very flexible transport cooling systems with dry ice, like the Messer Siber Container Cooling System, maintain the temperature for chilled or frozen products. Messer see a good future for industrial gases in the food processing industry. This is confirmed by our business development where food is one of the fastest growing segments supplied by Messer.”

So while new systems, techniques and innovations may come and invariably go, it’s clear that the industrial gases industry will still have a significant role to play in the future of food processing, in both cryogenic freezing and the increasingly popular MAP technologies.

CO2 versus LIN?
Both gases have their merits but when to use either, depends on the availability and cost of supply of each. In Thailand, for example, there is plenty of CO2 available from natural gas rejection and so has been used for freezing and chilling prawns on a large scale (>400 000 tons per year). However, there is more to it and sea food processors have found that the use of LIN is too extreme (too cold), causing the prawn tails to fracture or shatter compared with the warmer CO2 refrigerant gas which produces a better quality product – so CO2 wins the day on that application.

Drinks Carbonation
To deliver the fizz in many of the drinks we know and love, a high quantity of dissolved CO2 is required. This carbonation can be obtained naturally of course, in drinks such as beer or sparkling wine, or artificially achieved by injecting CO2 into a liquid, as is the case with many soft drinks and in most pubs, bars and nightclubs.

The CO2 reacts chemically with water molecules to form carbonic acid (H2CO3) and works well when the water or liquid is under pressure, providing that tingling, gaseous fizz to our drinks.