In 1857 Pasteur left Lille and returned to Paris, having been appointed manager and director of scientific studies at the École Normale Supérieure. That same year he presented experimental evidence for the participation of living organisms in all fermentative processes and showed that a specific organism was associated with each particular fermentation. This evidence gave rise to the germ theory of fermentation.
In 1863, at the request of the emperor of France, Napoleon III, Pasteur studied wine contamination and showed it to be caused by microbes. In 1864 Pasteur discovered that heating beer and wine was enough to kill most of the bacteria that caused spoilage, preventing these beverages from turning sour. The process achieves this by eliminating pathogenic microbes and lowering microbial numbers to prolong the quality of the beverage.
He then invented a process where bacteria could be removed by heating the wine to 50–60 °C (120–140 °F) then cooling liquid, a process now known universally as pasteurization. He completed the first test on April 20, 1862. Today, pasteurization is used widely in the dairy industry and other food processing industries to achieve food preservation and food safety.
The custom of preserving milk by heat may be ‘as old as the cow and the use of fire'. William Dewes recommended heating milk in the home before feeding to infants some 40 years before Pasteur conducted his experiments. Dewes observed that if the milk was heated to boiling point and cooled quickly, the tendency to spoil was reduced. Also preceding Pasteur was the contribution of Gail Borden who, in 1853, patented a process for heating and condensing milk under vacuum followed by addition of sugar for preservation.
Pasteurization was named after Louis Pasteur, who applied heat treatment to improve the shelf life of wine. Later, the process was applied to milk. Originally, the temperature–time combination for pasteurization was based on the amount of heat treatment required to destroy Mycobacterium tuberculosis var. bovis, which caused tuberculosis and was considered to be the most heat-resistant pathogen in milk at the time. Currently, the temperature–time setting is based on thermal death time studies for the most heat-resistant pathogen found in milk, Coxiella burnetii, which causes Q fever.
Invention
of pasteurization process by Louis Pasteur
