Extending shelf life and reducing costs the superchilling way

A team of Norwegian scientists have developed a better method of extending the shelf life of fish and meat products. Known as superchilling, the new technique also reduces associated storage and transport costs.

The scientists are based at SINTEF Energy Research in Norway. SINTEF is the country’s Foundation for Scientific and Industrial Research at the Norwegian Institute of Technology and is the largest independent research organisation in Scandinavia.

The new technique involves chilling fresh fish or meat to one or two degrees below zero so that it stays fresh for longer. Tests at SINTEF have shown that superchilled salmon fillets stay fresh four or five days longer than when treated with conventional chilling. The shelf life of pork chops treated in the same way can be extended by as much as 26 days.

“The technology is partly a matter of freezing, but the content of ice is so low that the products taste just like fresh food,” explained Anne Karin Torstveit Hemmingsen, who leads SINTEF’s superchilling efforts.

The secret is to chill the meat or fish to a much lower temperature than the fridge temperature of about 4°C or so that has been usual until now. SINTEF has shown that the products kept best if they are stored at a temperature of between one and two degrees below zero.

“The process results in what is known as ‘shell freezing’. Superchilling also makes it less likely that the products will disintegrate during the production and packing processes,” she added.

If fish is slowly frozen, large ice crystals form, which damage muscle structure. Fast and controlled superchilling, just below freezing point, will only freeze the loose-bound water, claims SINTEF. The amount of ice crystals that form will depend on the product type and conditions, but below a critical level.

The scientists have tested cold air tunnels to superchill food. Depending on the volume of products and other factors, food can be superchilled in minutes. Research is being conducted to find the optimum method of superchilling different products within different environments.

This year, the scientists are researching the use of brine as an ice substitute. They are testing whether superchilling using brine will form less ice crystals, providing another method for storing fish, in particular.

SINTEF claims an important discovery is that food stays fresher for longer if the post-superchilled temperature is kept constant, and therefore the ice structure remains unchanged for longer.

Several years of research on chilling technology of this sort have resulted in serious financial support from the Research Council of Norway and Norwegian industry. Together with colleagues from other departments of SINTEF, NTNU, Matforsk and industry, the SINTEF Energy Research scientists will be running a NOK30million research project (E3.7m) over the coming five years.

Superchilling is one of five work-packages that make up the project entitled ‘profitable food processing’.

The aim of the project is to make the Norwegian food-processing industry more competitive in the global market. A longer shelf-life will make it easier for the Norwegian fishing industry to export fresh fish, since it is a long way to European markets. Superchilling allows transport costs to be greatly reduced because ice is no longer needed in the fish boxes, which means that refrigerated trucks can carry more fish.

Nortura, a merger of the Gilde and Prior food companies, will soon open its first superchilling plant, and the company has great expectations of the new technology. The final goal is a superchilled chain all the way to the chilled-foods counter, and even better product quality that will benefit consumers.

SINTEF and NTNU’s superchilling work has already attracted international recognition with three of its researchers being awarded a diploma at a recent congress in Istanbul.

Accepting the award on behalf of his three colleagues, Anders Haughland explained that superchilling is a combination of fresh and frozen goods when it comes to durability. However, he added that the quality should be as good as fresh food and preferably better.

Haughland said food prepared from correctly superchilled raw materials is juicier and has more flavour. In tests carried out with Gilde on the production of seasonal ham, for example, it was found that keeping a lower temperature through the processing preserved the juice in the meat in a much more satisfactory way than when conventional methods are used.

As well as greater durability and better quality, the congress also got an insight into the way that production costs are affected by the new technique. Norway is a major exporter of unprocessed fresh salmon, although much of the cargo is the ice used to package the fish. More than 100 fully-laden trucks leave the country every week with the salmon and each costs about NOK25000 (E3000) in transport charges. However, when superchilling is used, there is no need for ice outside of the product. Each truck carries more fish, with overall savings in transport costs estimated to be in the region of millions of Kroner every year.

Atmospheric freeze drying

The superchilling success builds on earlier research carried out at SINTEF. Norwegian company Dtech is a spin-off of SINTEF and NTNU and its Hungarian plant uses atmospheric freeze drying technology developed by the two to supply the international food industry with dried maize and dried peas – ingredients that will end up in dried soups and powdered casserole dishes all over the world.

Today, Dtech is a market leader in atmospheric freeze drying technology, and seeks to become the preferred supplier to a number of key providers of dried fruit and vegetables by commercialising several patents.

Its novel atmospheric freeze drying technology has already been implemented at Aroma Dry's factory in Hungary which aims to be a reliable and profitable producer of freeze dried corn and peas in Europe. This factory was finished in spring 2005, and is currently 100 percent owned by Dtech. In addition to this, Dtech makes use of a pilot testing plant in Norway, at Arctic Aroma, which is using the same process.

Atmospheric freeze drying is a patented technology that uses heat pump systems in combination with a fluid bed dryer. The product undergoes a drying process in which the temperatures start below freezing-point and then rise above it. The heat pump dehumidifies the air, condenses the water vapour and conserves the heat. This way of drying, in addition to the fact that there is a very high mass and heat transfer, makes the process less expensive, easier and far more energy efficient than competitive methods.

The drying facilities are built in two separate drying steps that can operate independently of each other, normally with different drying temperatures. In the first step approximately 90percent of the water is removed, the rest of the water is removed in the second drying step.

Atmospheric freeze drying can be applied to a variety of products. A prime dried food product should retain its taste, colour and shape, and should have a short rehydration time.

The drying temperature is of great importance to the quality, and this can be precisely regulated in the heat pump dryer. The exact control of the drying parameters gives the ability to manipulate the quality of the product specified by each customer.

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