Freezing guarantees product quality and storage life

Cold chains are temperature controlled supply chains. That means that on their path from the producer to the consumer certain products have to be kept, transported and stored continuously under defined temperature conditions at each individual trade level. Cold chains guarantee the storage life of seafood products, linking up far-off regions of the world and thereby enabling global trade.

The theoretical shelf-life of many products can often only be achieved if they are kept constantly within a certain temperature regime. The list of temperature sensitive goods is long. It includes fresh foods such as fruits, vegetables and meat but also some chemical and pharmaceutical products. The cooling requirements of fish and seafood products are particularly high, however. They have to be kept constantly at low temperatures so avoid premature spoilage.

Heavy ice blocks weighing 10 to 25 kg have been produced using Linde’s freezing units for nearly 150 years. They are still in use today in some regions of the world.

Although the term “cold chain” is widespread today and most people are familiar with it, it only partly addresses the heart of the problem. Not all products are similarly sensitive, their temperature requirements and tolerances can differ. Some products have to be kept at a low temperature constantly to achieve a maximum shelf-life, while others tolerate slightly higher temperatures and even short-term temperature fluctuations. Some fruits, for example, last longest at temperatures of around 13°C. That is why in the food industry this temperature is often simply called “banana”. “Chilled” products are to be found in the range between 0 and 2°C. “Frozen” is used for products around -18°C and “deep frozen” is in North America even nearly -30°C. Because the term cold chain does not cover all temperature ranges and requirements the phrase “temperature controlled logistics” is more fitting today.

It has been known for centuries that keeping fish and seafood cool can lengthen their storage life. Reports from the year 1797 confirm that English fishermen already at that time cooled their catches with ice. In order to be able to cool the fish in summer, too, they stored sufficient ice during the winter. To this purpose blocks of ice were sawn from lakes and stored in cellars. The world’s first functioning refrigerating machine was built by John Gorrie in Florida in 1845. He applied for a patent in 1851. Gorrie’s invention was a commercial failure but Carl von Linde’s ammonia compressor refrigeration unit marked the breakthrough in 1874 and the beginning of the development of an independent refrigeration industry. Not long afterwards the cargo ship “Paraguay” transported frozen products across the Atlantic for the first time: 80 tonnes of frozen mutton were taken from Buenos Aires to France. In the year 1882 the “Dunedin”, the world’s first special vessel solely for the transport of frozen goods, went into operation. At the same time the first cold stores were built that were fitted with refrigeration facilities that made them fully independent. This provided the basis for the development of cold chains that today connect all regions of the earth in a tight network and constitute an elementary prerequisite for global trade with fresh, perishable and frozen products.

This development was encouraged on the one hand by the big colonial powers which could thereby promote trade with their colonies. In 1902 the United Food Company took the first refrigerated banana vessel into service. It was able to carry the exotic fruit in optimal ripeness to destinations all over the world. Great Britain obtained about 600,000 t of frozen meat from its colonies in 1910. The rapidly growing refrigeration capacities also enabled longer storage of food, making it possible to build up stocks and thus provide disadvantaged regions of large territorial states such as in the USA with better, more stable supplies.


Freezing fish caused problems at first

Whilst it was already common to cool fish a good hundred years ago, freezing fish still presented some problems at that time. Freezing meat and vegetables really worked right away with satisfactory results but in the case of fishes the results were not so good and varied considerably. We know today that this was mainly due to the freezing technique. The fish was simply put into cold storage at a temperature of minus 20°C. In this cold, motionless air it took 36 hours and more for it to freeze completely. When freezing takes so long, however, part of the tissue fluid is released from the muscle tissue. It accumulates between the muscle fibres and freezes there forming large ice crystals, thereby increasing the internal pressure in the muscle due to the increase in volume. This presses the muscle tissue together, causing even more fluid to be released and tearing the connective tissue. When the fish was thawed again later water was lost and with it also the salts and aroma products dissolved in it (drip loss). The damaged connective tissue offered less support and the meat often fell apart during filleting or when heated. Because the quality of the defrosted fishes was much reduced it was at first thought that fishes were not suited to deep freezing.

Cryogenic freezers that use liquid nitrogen or carbon dioxide as a refrigerant enable particularly fast deep freezing which also helps maintain quality.

This, however, was not consistent with observations made by the biologist Clarence Birdseye among the Inuit in Labrador. When fish was taken out of an ice hole there in the biting cold it froze within a few minutes and became rock hard but did not seem to lose any of its quality or flavour properties. The transfer of this observation into practice, its industrial use and exploitation was to take years, however.

Even experts saw deep freezing at that time only as a temporary method of preserving foods for the food industry, particularly for the storage of sensitive products and as a product buffer. That was understandable for, after freezing the products, the chain was broken. Trade with such products was hardly conceivable because the necessary infrastructure was lacking. In developed industrial countries the railway often already had refrigerated trucks but for road transport, i.e. for transport over the “last mile”, the prerequisites for appropriate presentation at the retailer’s or for storage at home in the deep freeze were completely lacking.

In spite of that, the history of today’s frozen food begins during those years. In 1911 the Danish fish importer A.J.A. Ottesen was granted a patent for the first viable industrial freezing technique. Ottesen froze the fish not in the air but packed it in an almost saturated brine solution (about 29% salt) that was cooled to -20 to -22°C. Under these conditions even large cod froze completely in one to three hours. Brine has a high density and a large heat absorption capacity. It wraps itself around the fish completely and has maximum surface contact. That is why the fish freezes much faster than in motionless air. With the Ottesen freezing technique (which anticipated today’s shock freezing) it was for the first time possible to freeze fish in high quality.

In April 1924 a specially founded consortium bought the Ottensen patents in Germany for the fast freezing of fish. Initial experience with the method was successful and the “Kühlfisch-Aktiengesellschaft”, the first German frozen food company, was founded in Wesermünde in May 1925. The company grew rapidly and soon hired a building in Bremerhaven. After necessary conversion to enable the freezing of fish the company was considered at that time to be the most modern fish processing company in Germany.


The first step was the development of national cold chains

Whilst the market for frozen fish grew slowly in Germany and other European countries things progressed much further in this field in the USA. The food industry had recognized in deep freezing the chance to solve the supply and transport problems satisfactorily in rural regions of the huge country. They used a technique that Clarence Birdseye had developed based on the freezing method practised by the Inuit: they had placed the fish onto the ice of the lake whereupon it froze almost instantly from the cold below. In Birdseye’s freezer the cold even acts on the fish from two sides for the fish is sandwiched between two movable aluminium plates in which liquid ammonia circulates as a refrigerant. During evaporation it absorbs so much heat from the fish between the plates that it freezes. An ingenious idea that Birdseye perfected further in the 1920s. When he sold the patents and brand rights on his invention in 1929 to the later General Foods Corporation it was already possible to freeze up to 6 t of foods per day using transportable plate freezers.

With regard to the development of cool and cold chains the USA were at that time also well ahead of the rest of the world. In 1913 a refrigerator with its own cooling system was sold for the first time in Chicago for home use. In the following years electrically and gas powered refrigerators competed for consumers' favour and it was not until after 1920 that the electrical devices asserted themselves when halogenated hydrocarbons, also called freons, came onto the market as new refrigerants. On 6 March 1930 a new era then began in ten food stores in Springfield (Massachusetts) when for the first time in the world industrially produced and packed frozen foods were offered for sale. The range of the brand “Birds Eye Frosted Foods” comprised mainly vegetable products such as spinach but also fish fillets. Later followed frozen fruit juices and components for ready meals. The frozen products were still presented for sale in deep freezes that were actually intended for ice cream. The appropriate infrastructure that would make trading frozen products successful and profitable was still lacking.

The term “cold chain” with which everybody is familiar today finally came into being in the 1930s. Already at that time it implied a continuous system for keeping products cool during transport and storage on their way from the producer to the end user. Whilst on shore freezing was at that time in principle conceivable, freezing at sea still presented problems. This did not change until the early 1930s when the first on board freezing technology became available and could be installed on fishing vessels. As from then completely new fisheries concepts were developed in Germany and other countries and fishing trips no longer only lasted a few days but could be extended to six to eight weeks. Instead of individual vessels, whole fleets could visit the fishing grounds in whose centre a parent vessel equipped like a factory was to be found. It took the catches of the smaller fishing vessels on board and processed them immediately to frozen fillets, fish oil, fishmeal and the like.


Specialisation in the frozen foods industry was inevitable

Although these projects were initially stalled or delayed by the outbreak of the war they already pointed to the future direction which developments in this field would take: the growth of large companies that were specialised solely in the production, transport and storage of chilled and frozen products. So developments moved away from all-rounders who occasionally froze some of their products to highly qualified specialists who have all the technical prerequisites and the necessary know-how for freezing.

With the exception of canned and dried products all seafood products are now traded chilled or frozen on the world market. A complex system of safe, reliable cold chains connects countries and continents, stretching into almost every corner of the earth. New technologies have made transport of temperature controlled goods on the road, in the air and by sea not only faster but also more easily predictable. What took a month in the past today often reaches its destination already in one week or ten days – whilst complying with all temperature requirements. Frozen seafood from Australia, Africa or Asia is in the meantime taken for granted in Europe as part of the range of available products at the retailer’s just as much as fresh fish that is caught directly off one’s own coast. And this development is by no means complete. Nearly everywhere in the world money is being invested in chilling and freezing technology to enable connection with existing trade channels and  improve opportunities within world trade. Without functioning cool or cold chains Chile’s export oriented seafood industry, for example, would be cut off from the important markets in North America and overseas.

Functioning cool and cold chains enable fish, seafood and other temperature sensitive foods to reach the consumer safely in top quality. At the same time they also constitute elementary components of the globalisation process. Worldwide exchange of goods demands from all participants adherence to certain standards – standards that have to be legally binding. All process-related data and parameters have to be measurable, analysable and controllable and they also have to be documented, for only then can the health risks connected to global supply chains be limited and individual product quality requirements guaranteed. In this respect cold chains today belong in a broader sense to Good Manufacturing Practice (GMP) and are mostly managed within the framework of in-company quality assurance. Numerous service and control companies have specialised in making procedures and processes within the cold chains controllable and, with the help of technical devices, validatable. Special test methods for checking the quality of transported products have been developed. Data loggers or RFID chips record temperature profiles meticulously during storage and transport, in containers, on trucks and within retail chains to enable conclusions to be drawn on the products’ remaining shelf-life.

The range of frozen seafood products, both individual components and complete ready meals, is constantly increasing and it is becoming more diverse and varied.


Logistical basis for cold chains is increasingly broad

Product packaging varies in respect of type and size. Depending on requirements the choice ranges from small temperature insulated polystyrene boxes that are kept cool with gel packs or dry ice to large independent containers with their own refrigeration systems. In the global freight business refrigerated containers have asserted themselves within just a few decades as the common transport unit. At the beginning of the 1980s containers were used for about one third of ship transports requiring temperature control. In the year 2013 they had a share of nearly three quarters of refrigerated freight. Containers are a universal and internationally standardized transport unit that is compatible with intermodal transport systems all over the world. Whether ship, train or truck: the ISO reefer container fits everywhere and can be easily carried. In 2011 about two million standardised 20 foot containers with their own refrigeration systems were in operation; that is equal to nearly 5 per cent of all TEUs (twenty foot equivalent units) in the global movement of goods. They practically constitute the backbone in the system of international cold chains and are completed by reefer ships in regular service, rail freight, refrigerated trucks and refrigerated transporters. The routine interplay of all participants makes it possible to close cold chains right up to the last mile and carry sensitive products safely and reliably to the retailer and the final consumer.

The growth prospects of chilled and frozen products are still far from exhausted in some regions of the world. Whilst frozen products are well accepted by consumers in industrialised countries, for example, in Asia they often still have the reputation of being a kind of food substitute. There, nutrition is mainly based on fresh products, and frozen food is almost meaningless. This is likely to change rapidly if the economic upswing continues and even more people migrate from rural areas to the big cities. Supplying large cities and urban centres will hardly be possible solely with fresh foods. And if the standard of living rises and demands on foods increase it will hardly be possible to get by there either without reliable cold chains. In the developed countries of Europe and America already 80 to 90 per cent of all foods are transported and traded within cold chains and the loss rate is below 5%. In contrast, only 25% of meat products and just 5% of fruit and vegetables are refrigerated in China. The share in the fish and seafood segment is even lower. That means there is a lot to do in this area in the coming years.