Example: Yesterday I bought some Salsa which contains tomatoes, how does a jar of tomatoes stay fresh and safe to eat for months in store shelves where actual tomatoes only last a week or two?
In: Chemistry
That salsa is canned at boiling (or higher) temperatures and has the pH lowered below 4.6 by adding vinegar, lemon juice or citric acid. The jar is sealed during the canning process by a wax-like gasket in the lid that forms an air tight seal with the top of the jar.
Jars are commonly canned with water, which boild at 100 deg C (at sea level). But at higher pressures, water has a higher boiling temperature. So sometimes jars are canned in a higher pressure environment.
The high temperature kills bacterial, mold and fungi (except for Clostridium botulinum, which produces boil resistant spores). Clostridium botulinum produces the deadly toxin botulism, but cannot grow at pH lower than 4.6.
The National Center for Home Food Preservation (NCHFP), which operates at the University of Georgia in conjunction with the US Department of Agriculture (USDA), has a lot of information on this, including tested safe recipes:
* https://nchfp.uga.edu/how/can_home.html
* https://nchfp.uga.edu/how/general/ensuring_safe_canned_foods.html
Latest Answers