A Brief Overview of Canning
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Although it may seem like a quaint pastime now, the invention of canning was a
revolutionary event in the history of food systems. The process as we know it today was invented in France in 1809 as a response to a contest spearheaded by Napoleon Boneparte. Napoleon was having a difficult time maintaining supply lines to his enormous army and needed new technologies for preserving and transporting food. The winning contestant, Nicolas Appert, invented canning, and the rest is history. Today canned food is a 94 billion dollar industry and about 97% of us will have canned food in our pantries at any given time. It is an often
overlooked technology, but our global food system is thoroughly reliant on it. As a food preservation technique, it is second in importance only to freezing/refrigeration.
How does canning work?
Canning works based on two basic principles that we all understand intuitively:
1) Heat kills microorganisms
2) New microorganisms cannot get inside of a container if it is sealed
Those two simple facts explain canning at a basic level. When we preserve food through canning, we use either a boiling water bath or a pressure canner to apply heat which kills the microorganisms inside the food. We also used specialized jars that seal up after they are heated, thus making sure that new microorganisms cannot get into the food after it has been heat treated. The combination of killing existing microbes and preventing new ones from getting into the jar, means that the food is effectively preserved from microbial deterioration.
What is the difference between a boiling water bath canner and a pressure canner?
A boiling water bath canner is exactly what it sounds like – a pot filled with boiling water. Since it uses boiling water, it can reach a temperature of 212 degrees fahrenheit (but no higher). Instead of boiling water, pressure canners rely on trapping steam pressure inside a vessel, and thus can generate temperatures much higher than boiling water. When we use a pressure canner, we are shooting for a temperature of 240 degrees fahrenheit. That explains the difference between the two types of canners, but why are the two types needed? Why not just use one of them? The answer lies with another important feature of canned foods: their pH
The importance of pH in canned foods
pH is a measurement of how many free hydrogen ions are present in a solution. In more conventional language, it is a measure of how acidic or basic something is. Acidic food ingredients like vinegar or lemon juice have very low pH (between 2-3), and basic food ingredients like baking powder have very high pH.
If the pH of a food is below 4.6 it can safely be preserved using a boiling water bath canner, because spore forming bacteria that can survive the temperature of boiling water cannot grow at a pH of 4.6 or lower. If the pH of a food is above 4.6, it must be processed in a pressure canner which can generate temperatures high enough to kill spore forming bacteria. Ultimately, that is why some canning recipes call for a water bath and some call for a pressure canner.
Why you must only use tested recipes from trusted sources
If food is canned properly it can be safe to consume for years. However, improperly canned food can be deadly. Without expensive lab equipment, it is impossible to be certain that a recipe has the right pH and the right time of heat treatment to be safe. That is why it is so important for us to only use canning recipes that have been developed and tested by reputable sources, like the NC State extension and other state extensions.
The link below will bring you to the website for the National Center for Home Food Preservation, which is a great source of tested canning recipes from trusted sources. If you employ proper technique, and follow the recipes from their site, you can feel confident that your canned food will be safe to consume.
National Center for Home Food Preservation Website: Nchfp.uga.edu