Appertisation

History marches on thanks to a competition

The French-German ‘confectioner’ Nicolas Appert (1749-1842) developed a completely new process for preserving food using heat. He carried out his research in the late 18^th century, at a time when the provision of food for armies posed a significant problem. The French government launched a competition with a prize of 12 000 gold francs for the person who could find a way of preserving food for soldiers. Appert won this prize in 1810 and, in the same year, he made his discoveries public in The Book for All Households or The Art of Preserving Animal and Vegetable Substances for Many Years.

Preserving food at home, tinned food

Pasteurisation and sterilisation of food involve heat treatment. Appertisation is a process which involves heat treatment and hermetic sealing. The food to be preserved is defined by its bacteriological status and its acidic or alkaline chemical nature, its pH. Depending on the type of food to be preserved, the heat treatment is performed at a higher or lower temperature (T) for a longer or shorter time (t). Appert’s book gives a list of foodstuffs and describes the temperature and the time needed for them to undergo this treatment.

The homemade preserves produced nowadays match the description given by Appert in his 1810 book The Art of Preserving. The process involves filling a glass container with the food to be preserved, sealing it carefully and hermetically and subjecting it to heat treatment at a specified temperature and for a specified length of time, then cooling it rapidly. Household sterilising pots can be used for appertisation at temperatures below 100°C. The reduction in pressure produced by condensation of the steam inside the container during cooling maintains the hermetic seal. Throughout the first half of the 20^th century, popular brochures and advertisements from glassware factories and home economics schools encouraged housewives to make preserves. Preparing homemade preserves was a national duty during both World Wars and was encouraged by the authorities and taught in classes in towns and villages.

In the 19^th century, Appert’s method of preserving food was applied before it was actually explained. He was unaware of the scientific principles behind it. In the 1850s, Louis Pasteur (1822-1895) a chemist and bacteriologist, demonstrated the biological laws of appertisation, which destroys micro-organisms and enables products to be preserved at room temperature. While Appert advocated the use of bottles and glass jars, the English soon developed the process using metal containers. These were filled and welded and then sterilised in an autoclave, a kind of large pressure cooker. This ensured the same pressure both inside and outside the tin during and after sterilisation, thus preventing it from becoming deformed. At that time, welding used a mix of lead and pewter which proved to be highly toxic, hence such welding was prohibited from 1879 onwards. Cases of botulism and food falsification created mistrust in consumers and slowed down the democratisation of tinned food until the First World War.