Canning has been around for a long time, but in the last few generations, it's been relegated to a dark corner & deemed too dangerous and scary for common people. I consider it to be an absolute necessity and something that needs to be brought back into daily life before we lose the skill completely. So let's bring the dark & scary into the light.

Botulism.  The big, scary word that did more to destroy canning knowledge than anything else. Botulism is a condition caused by a powerful neurotoxin, which is produced by the bacterium Clostridium botulinum. The toxin grows in low oxygen, low- acid, low-sugar/salt conditions. The bacteria is found in the soil and is so common, that you can assume all foods grown in soil have it present on them. The danger is when the bacteria secretes the toxin. Active bacteria is killed in the normal cooking process. Dormant bacteria spores require pressure canning to destroy them. C. botulinum cannot grow below a pH of 4.6, so acidic foods, such as most fruits, tomatoes, and pickles, can be safely processed in a water bath canner. 

You cannot see, smell, or taste the toxin. The guaranteed way to negate the risk is to dump the contents into a pot and bring it to a rolling boil for 10 minutes or bake it at 185 for 5-10 minutes or at 176 for 20 minutes.  A standard casserole or pie is baked at 350* for 30+ minutes. This temperature will kill the spores.

The last case of botulism poisoning from home canned food was in 2024 in California when someone brought a salad to a family picnic that contained home canned prickly pear cactus pads. Between 2017 and 2021, there were a total of 20 cases of foodborne botulism specifically linked to home canned food. That is an average of 5 cases per year. 

Pressure canners. A pressure canner speeds up the canning process and processes low acid foods more safely than a waterbath. You put a few inches of water in the bottom of the canner, put in your jars, seal the lid and turn the heat on. It comes to a boil under pressure and steam starts coming out the open vent. Once the steam starts, you let it "vent" (constant stream of steam) for 10 minutes to make sure all cooler air pockets are removed and only high- temperature steam remains in the canner. Then you put the weight over the vent. Bring it up to pressure, lower the heat to keep it at that pressure, and wait until your time is up. Turn off the heat, wait until the pressure reads 0, take off the weight to let the steam vent again. Wait about 15-20 minutes and then remove the lid & use a jar lifter to remove the very hot jars. Put the jars on a towel to protect them from a cooler counter so that they don't crack, and then leave them alone until they are cool.

Pressure canners are a relatively new invention. They were introduced in 1851, although a pressure cooker (digestor) was designed in 1679 to make food soft. Prior to 1851, home canned foods were canned using a waterbath. Meat was canned in a waterbath for 3 hours. Introduction of the pressure canner decreased that time to 90 minutes. That's a lot of time saved monitoring a stove or a fire to maintain a boil.

Waterbath canners. Waterbathing was the original method of preserving food. Originally in tin cans, and then in glass when glass jars became common. The basics of waterbathing are to fill a hot jar with hot product and put into a hot pot of water.  (Cold/cold/cold is also an option, but bringing them up to temp takes longer). Boil until food is processed, and then remove & let jars cool while the next batch is done. Low acid foods need an acid added to prevent the growth of the neuro toxin that causes botulism, and food needs to be boiled long enough to kill off any bacteria that might be growing. On average, that's around 3 hours. In the US, this practice is called rebel canning. It has not been scientifically tested, and therefore is not considered "approved" or "safe". Around different parts of the world, and in the Amish communities, this practice is still in use. In my opinion, it works just fine, but the amount of time it takes makes the purchase of a pressure canner worth it to me; especially because you can waterbath in a pressure canner, but you cannot pressure can in a waterbath pot.

High acid foods can be waterbathed in shorter times because the acid prevents the growth of toxins. In these cases, the purpose of the waterbath is to kill any yeast, mold or bacteria, heat the jar contents enough to remove any air, and to soften the rims of the lids so that they seal to the jars. 

A high acid food is considered 4.6ph or lower. Most fruits and berries fall into this category, as well as pickles & fermented foods. Tomatoes are right on the edge of acid, so usually vinegar, citric acid, or lemon juice is added to tip them over into the high acid category. Bottled lemon juice is recommended because it has a guaranteed, uniform level of acidity. You can also utilize ph test strips to confirm that your product meets the needed 4.6 or below to make short waterbath times acceptable.