Processed meat is considered to be any meat which has been modified in order either to improve its taste or to extend its shelf life. Methods of meat processing include salting, curing, fermentation, and smoking. Processed meat is usually composed of pork or beef, but also poultry, while it can also contain offal or meat by-products such as blood. Processed meat products include bacon, ham, sausages, salami, corned beef, jerky, canned meat and meat-based sauces. Meat processing includes all the processes that change fresh meat with the exception of simple mechanical processes such as cutting, grinding or mixing.
Meat processing began as soon as people realized that cooking and salting prolongs the life of fresh meat. It is not known when this took place; however, the process of salting and sun-drying was recorded in Ancient Egypt, while using ice and snow is credited to early Romans, and canning was developed by Nicolas Appert who in 1810 received a prize for his invention from the French government.
Relationship to cancer
The International Agency for Research on Cancer at the World Health Organization classifies processed meat as Group 1 (carcinogenic to humans), because the IARC has found sufficient evidence that consumption of processed meat by humans causes colorectal cancer.
A 2016 report by the American Institute for Cancer Research and the World Cancer Research Fund found that processed meat consumption increased the risk of stomach cancer. A 2012 paper by Bryan et. al. identified Helicobacter pylori as a potential causative agent that warranted further study.
The preservative sodium nitrite (E250) (mixed into curing-salt) is well known for its role in inhibiting the growth of clostridium botulinum bacteria spores in processed and refrigerated meats. A principal concern about sodium nitrite is the formation of carcinogenic nitrosamines in meats containing sodium nitrite when meat is charred or overcooked. Such carcinogenic nitrosamines can also be formed from the reaction of nitrite with secondary amines under acidic conditions (such as occurs in the human stomach) as well as during the curing process used to preserve meats.
Nitrate and nitrite are consumed from plant foods as well as animal foods, with 80% of a typical person's nitrate consumption coming from vegetables, especially leafy and root vegetables such as spinach and beets. Some nitrate is converted to nitrite in the human body. Nitrite is classified as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration, and is not directly carcinogenic. Yet, when nitrate or nitrite interact with certain components in red meat, such as heme iron, amines, and amides, they can form nitroso compounds, which may contribute to the association between consumption of processed meats and higher incidence of colorectal cancer.
- Pearson, A. M.; Tauber, F. W. (2012-12-06). Processed Meats. Springer Science & Business Media. ISBN 9789401096928.Introduction 
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- Oostindjer, Marije; Alexander, Jan; Amdam, Gro V.; Andersen, Grethe; Bryan, Nathan S.; Chen, Duan; Corpet, Denis E.; De Smet, Stefaan; Dragsted, Lars Ove; Haug, Anna; Karlsson, Anders H.; Kleter, Gijs; De Kok, Theo M.; Kulseng, Bård; Milkowski, Andrew L.; Martin, Roy J.; Pajari, Anne-Maria; Paulsen, Jan Erik; Pickova, Jana; Rudi, Knut; Sødring, Marianne; Weed, Douglas L.; Egelandsdal, Bjørg (2014). "The role of red and processed meat in colorectal cancer development: a perspective". Meat Science. 97 (4): 583–596. doi:10.1016/j.meatsci.2014.02.011. PMID 24769880.
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- Meat processing technology for small- to medium-scale producers Gunter Heinz, Peter Hautzinger, Food and Agriculture Organization of the United Nations (FAO) Regional Office for Asia and the Pacific (RAP), Bangkok, 2007, ISBN 978-974-7946-99-4
- Pearson, A. M.; Tauber, F. W. (2012-12-06). Processed Meats. Springer Science & Business Media. ISBN 9789401096928.Introduction