Essentials of Thermal Processing. Gary Tucker S.

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1 History of Thermal Processing

      The application of high temperatures is one of the most commonly used methods to kill or control the numbers of micro‐organisms present within foods and on packaging surfaces. Evidence for its importance in today's food industry can be seen in the percentage of shelf space taken up in any retailer by foods preserved by heat. Along with low temperature storage (e.g. refrigeration and freezing) and dried foods, thermal processing remains of key importance to the worldwide food industry. There have been many attempts to introduce foods preserved by new technologies (e.g. ultra high pressure, pulsed electric fields) into retail food markets, but their significance is still relatively minor in comparison with thermal processing.

      Thermal processing is a general term that describes all forms of heat treatments in which micro‐organism numbers are controlled by heat. This includes heat processed container types such as metal cans, plastic trays, pouches, glass jars, and even cartons. It also includes continuous thermal processes that take place outside of the package and are usually linked with aseptic or hot filling. Nowadays, the terms ‘canning’ and ‘thermal processing’ are often used interchangeably; however, as most of the original work was done in cans, thermally processed foods that are in other packaging formats are still often referred to as ‘canned’.

1.1 A BRIEF HISTORY OF THE SCIENCE AND TECHNOLOGY OF THERMAL PROCESSING

The early Greeks believed in ‘spontaneous generation’ (that living things could originate from non‐living matter). Although Aristotle discarded this notion, he still believed that animals could arise spontaneously from other unlike organisms or from soil. His influence regarding this concept of spontaneous generation was still felt as late as the seventeenth century.

      The sixteenth and seventeenth centuries were a time of great scientific advancement in areas of chemistry, mathematics, and physics. This was known as the Scientific Revolution which laid the foundations for the Age of Enlightenment in the eighteenth century, a period where science became popular with the ordinary person, and an increasingly literate population was hungry for knowledge, information, and to learn. Evening Science lectures, with demonstrations, were very popular as a form of entertainment for the working class.

      In addition at that time, the Industrial Revolution was taking place in Europe in the eighteenth and nineteenth centuries. Great strides were made in the areas of textiles, steam generation, and metallurgy. Steam generation was much more efficient; fossil fuels were used for the first time, instead of wood based fuel, resulting in a much more efficient source of energy. Advances in mining techniques and metal‐working, especially iron founding, resulted in many new uses for metals like iron, copper, and tin (http://www.wikipedia.org).

Towards the end of the seventeenth century, a chain of observations, experiments, and arguments began that disproved the belief that life could be generated from non‐life. Microbiology, as a science, can be said to have begun with the development of the microscope. In the mid‐seventeenth century, although not the inventor of the microscope, Antonie van Leeuwenhoek (1632–1723) (Fig. 1.1), a Dutch draper, ground his own lenses and made small microscopes that could magnify up to 500 times. He had exceptional attention to detail and was the first to provide proper descriptions of his observations, which included protozoans from the guts of animals and bacteria from teeth scrapings. His descriptions and drawings were excellent, and he conveyed his findings in a series of letters to the British Royal Society during the mid‐1670s. Although the observation of his ‘animalcules’ stimulated much interest, it remained as an oddity until the eighteenth century.

      In France, the French Revolution (1789–1799) took place, largely as a result of growing dissatisfaction due to poverty and a shortage of food and increasing malnutrition. The Napoleonic Wars (1803–1815) further influenced the economy and developments in Europe.

It was in this time that Nicolas Appert was working as a confectioner. He was born on 17 November 1749 at Charlon‐sur‐Marne. His family were not wealthy, and young Nicolas acquired an education largely through personal effort. He was trained as a chef and worked and experimented with different kinds of food processes (fermenting, distilling, and preserving) for his own interest all of his life (http://www.appert‐aina.com).