[ PROcessing ] tin can was invented. The British merchant Peter Durand had taken up the idea, only he did not put the food into jars, but sealed them airtight into metal containers. He sold the patent which he received for his invention in August 1810 to Bryan Donkin and John Hall who, three years later in Bermondsey opened the world’s first canning factory that used containers made of tinplated sheet iron to make food durable for a long time. In France, where the preserve was “invented” over 200 years ago, wellknown producers market their products in their own specialized shops.
is usually transparent and allows the consumer a visual assessment of the product in the jar. This may well be beneficial, but sometimes also a problem, depending on the state in which the product is presented and how it was processed. Whereas chunks and flakes of tuna, for example, are usually packed in cans, large attractive fillet pieces are often packed in glass jars that allow the consumer to see the outstanding quality of the contents. Another advantage of glass is that it can easily be recycled. The market share of glass jars would probably be even bigger if glass did not also have some significant disadvantages. For example: transparent material is not always suited to photosensitive products that fade or decompose under the influence of light. Glass is also relatively heavy, which puts a burden on the CO2 balance during transport, and also fragile, meaning that glass containers have to be handled with great care. The fragility of the material must also, of course, be taken into account already during the production of bottled preserves, although the process more or less corresponds to that of other types of food preserves. Canned foods can be strongly cooled immediately after autoclaving to prevent 50 Eurofish Magazine 6 / 2011
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overcooking which would have a negative effect on the consistency of the contents. This is often not possible in the case of glass containers because temperature changes of over 50 degrees put a strain on the glass and can cause it to break. Cost is another significant aspect: closing glass jars is a relatively expensive process. Twist-off metal lids are usually used today. The lid is held in position by the vacuum within the jar and by a slight turn which holds it firmly on the jar like a screw top. The safety of the seal depends on several factors. The upper edge of the jar must be clean and the rubber ring in the lid intact. The lid must be placed onto the jar perfectly horizontally and should snap into position correctly when twisted. Only then will the vacuum remain intact and this is the prerequisite for the perfect condition of the preserve. That is why there should an audible click when the twist-off lid of a jar of preserves is opened for the first time.
Tinplate, cold rolled thin steel sheet, whose surface is coated with tin by means of electrolysis to prevent corrosion, is still the preferred material for cans used in the food industry. The technology for producing tinplate is in the meantime so sophisticated that one gram of tin is enough to coat one square metre of steel plate with a 0.15 mm thin layer. For additional protection tin cans are often varnished on their interior or coated with a thin plastic film (full seal) because some foods that contain fruit acids can dissolve tin from the can metal. Although tin is vital for human beings and has to be absorbed with the diet the necessary intake is extremely low and can be covered easily. The World Health Organisation therefore recommends limiting the daily intake of tin from food to
2 milligrams per kilogram of body weight. Cans with an interior plastic coating release practically no tin into the food they contain. However, more recently, some of the substances that are used to coat food cans have come under criticism. The BADGE (bisphenol-A diglycidyl ether) that they contain can be passed on to the preserves in small amounts and this substance is suspected of being a possible carcinogen and mutagen. In the opinion of many experts this will not lead to any acute health hazard but the contamination is generally “undesirable.” The problem of slow poisoning by substances which pass from the cans into the food they contain is not new. In 1845, Sir John Franklin and his companions set out on an Arctic expedition to search for the Northwest Passage. Within three years, during which time they lived almost exclusively from canned food, they all died of lead poisoning. The contents of the cans were edible and not in any way spoilt, but at that time cans were soldered with lead.
Opening the cans remains a problem Today efforts are made to find better solutions to this problem and
Cans have to be laminated In the same year in which Napoleon bestowed on App ert the impressive prize for the successful testing over a number of years of his preservation process the
In Thailand and other supply countries tuna is generally packed in flat round cans. www.eurofishmagazine.com
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