The Science of How Home Canning Works

Home canning is a fun and safe way to preserve the summer's garden produce! Here's exactly how it works and the science behind it at Crunchy Mama Science!I got into home canning almost immediately after I got married. It was the first natural living thing I ever did and I instantly fell in love with it. For any of you who have canned, you know that it is a huge trial and error process. I can’t tell you how many times I had a scalding pot of water on the stove boiling over, food everywhere, and a thousand wet paper towels stacked up on my counter. However, there is nothing more satisfying than listening to those jars pop, pop, pop as they seal. And then, you have a pantry full of goodness that you created! However, if you are like me, you want to know why and how this works before ever touching the food in those jars.

During canning three things that must happen:

  • Enzymes must be destroyed
  • Microorganisms must be killed
  • Air must be prevented from re-entering

 How is this done?Home canning is a fun and safe way to preserve the summer's garden produce! Here's exactly how it works and the science behind it at Crunchy Mama Science!

Temperature and pH

pH is a number used to indicate the number of hydrogen ions in a solution.

0-6 is considered acidic, low pH

7 is neutral–water

8-14 is considered alkaline, high pH

As far as canning is concerned, anything less than 4.6 is high-acid  and anything greater than 4.6 is low acid.

High acid foods generally include anything with fruit and sugar including jams, jellies, chutneys, pie fillings, preserves, as well as anything with vinegar including all types of pickles, salsas, juices, and relishes. Low-acid foods include meats, vegetables, and some tomato sauces. Please consult the recipe to determine whether it is high-acid or low-acid.


Let’s start with enzymes. What are they? Enzymes are a special type of protein designed to catalyze (assist) in a chemical reaction.

Enzymes work at a specific pH and temperature. As the pH or temperature in which an enzyme functions increases or decreases, eventually the protein will denature (fall apart) and the enzyme is inactivated. For canning purpose, high heat is responsible for denaturing the enzymes in the food, thus stopping spoilage.

Vacuum Seal

This is very straightforward. As you fill jars when canning, you leave space for the food to expand. As it heats up the molecules spread out in response to the heat energy. When the jars are taken out of the water, the food cools off and the molecules begin to contract, sucking in the lid and forming a vacuum seal. This keeps any airborne particles from re-entering the jar in storage.

Home canning is a fun and safe way to preserve the summer's garden produce! Here's exactly how it works and the science behind it at Crunchy Mama Science!


Microbes cover much of our food, just as they cover our environment and our bodies. The problems occur when they are allowed to grow unchecked. It is generally agreed upon that at a pH of less than 4.6 food can be held at boiling (212 degrees F) for an allotted time to kill most of the bacteria and mold that will cause trouble. However, at pH levels of above 4.6, our friend Clostridium botulinum can grow.       

 C. botulinum is a bacterium that causes botulism, a deadly form of food poisoning that may cause muscle paralysis. Many people think of this when they think of home canning. It is in the same genus as both the bacteria that cause tetanus and the debilitating diarrhea people get after antibiotic use. C. botulinum is an anaerobic organism, which means it only grows in the absence of oxygen. Otherwise, it exists as a spore, which is kind of like a seed. These spores cannot grow in an acidic environment; however, they flourish in the low-acid environment of canned meats, vegetables, and anything greater than 4.6 on the pH scale. These spores are not killed at 212 degree F. If a jar is vacuum sealed (no oxygen) and left at room temperature, this creates the environment for C. botulinum to grow from the spores and produce the dangerous botulinum toxin. Ironically, this is the very toxin used in botox injections. A temperature of around 240 degrees F will kill the spores, and this is done with a pressure canner. All low-acid foods must be processed with a pressure canner for this reason.

Home canning is one of my favorite hobbies. I can preserve my garden produce, make fresh pressed apple juice for the year, sauces, condiments, canned tomatoes, and excellent Christmas gifts! The science behind home canning is relatively straightforward and is not a problem if recipes are followed correctly.  All you need know is that canning is really amazing and it is super simple when you get the hang of it! There are hundreds of excellent and safe recipes out there for you to try and many resources on safely canning at home. I encourage you to give it a try sometime! Of course, it helps to get some friends together and do it as a group. I absolutely love staring at all my goodies stacked nicely in my root cellar. Yes, I have a root cellar. And yes, one of the items in that root cellar is labeled Daddy J’s Good BBQ sauce.

Resources and Recipes:

What to do next?

Tell me in the comments, do you preserve food at home?

Prefer to ferment food instead? Check out THIS POST about fermenting your own food at home!

About Emily

Hi, I’m Emily. I’m a free range mama helping women conquer simple, healthy living with a side of science!

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