Is canning safe?
If you’ve done any reading on social media about canning, you’ll find a whole lot of strong opinions on whether or not canning is safe and a good thing to do. There are two extremes on the spectrum of whether or not canning is safe. On the one side is the Nervous Nelly who thinks that canning is just too dangerous: both the process (think exploding canner) and the food (every jar is an incubator for poison.)
On the other side is the Rebel Canner who advocates canning anything you want how ever you want. The sky’s the limit.
Who’s right?
Like any polarizing topic, there’s a little bit of truth to both sides. Before deciding who’s right, let’s talk about basic principles behind canning.
Air, bacteria and light are all things that can make food spoil. When we can food we are taking two
things out of the equation: we create a vacuum so that there’s no air and we heat the food to kill bacteria.
Destroy the bacteria
Simply boiling for 10 minutes or more will kill almost all bacteria. So if you heat the food to boiling while creating a vacuum, you will stop spoilage caused by bacteria. However, the biggest culprit in food poisoning from home canned food is the Clostridium botulinum toxin. This odorless, tasteless bacteria is present in the soil, which means it’s on most vegetables and most dairy products.
It can cause paralysis and even death. You definitely want to be careful about this very potent toxin. Even the smallest amount can cause lots of damage.
Don’t sniff newly opened jars of food. Remember: C. botulinum has no odor. and you risk inhaling the bacteria and having a bad reaction.
The thing about the C. botulinum bacteria is that it thrives in a low-acid vacuum. But it can’t reproduce in an acid environment.
Foods that have a pH of 4.3 or less, (like fruits, jams and pickled products) are hostile to C. botulinum. A simple water bath canning process will kill all the other bacteria that may cause spoilage.
But when you seal low-acid food (like canned meat or veggies) in a jar with any C. botulinum in it, you’ve created a lovely home for the bacteria to thrive.
In order to completely kill all C. botulinum the internal temperature of the food must reach 240° – 250° F, which is hotter than boiling water. That’s why low-acid foods must be pressure canned, because the pressure canner will get foods to that higher temperature.
Create a vacuum
Air is another catalyst for spoilage. So when you seal the food, you prevent new bacteria from getting into the jar and cause food to spoil. To create a vacuum, you need a bit of headspace in the jar. This is the room between the food and the lid. As the air heats, it expands and pushes air out of the lid. As it cools, the air contracts and sucks the lid down, creating a vacuum seal.
But remember: it’s not enough to just seal the jar.
You also need to kill the bacteria. That means keeping it at boiling temperature (which you get in water bath canner for acid foods) or above (which you get from a pressure canner for low-acid foods.) to be sure to kill all bacteria. If you just heat the food and put a lid on it or put it in a hot oven there is no guarantee that the internal temperature of the food is hot enough to kill all the bacteria. Yes, the lid will seal and yes, you’ll have a vacuum. But that’s not a guarantee that the food is safe.
Remember that C. botulinum loves a vacuum, so if you create a vacuum without killing all the C. botulinum, you may have a problem.
But doesn’t heat harm the food?
Yes, when you heat food, especially at very high temperatures and for a long time, the taste,
color, texture and nutrition of the food is altered. It’s a balancing act. You want the food hot enough long enough to kill the
bad stuff and get a good seal but not too much to make the food inedible.
That’s why there are some foods you shouldn’t can because the process changes the texture and flavor so much as to make it inedible. These include things like pasta, rice, avocados and dairy. (And, in my personal opinion, asparagus. Blech! To be clear, canned asparagus is perfectly safe to eat. But during the canning process it loses all its color, turns mushy and I think it just tastes nasty. Feel free to prove me wrong.)
But we’ve always done it this way.
Canning bread or cake
You may see advice for putting bread batter (like banana or zucchini bread) or cake batter in a jar, putting a lid on it and baking it. The bread or cake cooks in the jar and as the jar cools, the air contracts, creating a seal.
There are two problems with this:
First this does not guarantee good head space. You need enough space for the air to fully expand and leave the jar so that when it contracts you have a good seal. Can you really perfectly gauge how much the cake will rise during baking? When it’s finished baking will it leave enough headspace for the lid to fully contract and create a seal?
Second, this is a low-acid food. Remember that it’s not enough to just seal the jar. To prevent botulism in low-acid foods, you must be sure that the internal temperature (not just the temperature of the oven, but at the very center of the food) reaches 250°. Baked cakes and breads only get to about 200°, so there is no guarantee that all the botulism spores have been killed.
Canning dairy products
Canning dairy is another common “rebel canning” practice. The rationale is that since you can buy commercially canned milk, why not can it yourself?
The problem is that to thoroughly pasteurize milk, it needs to be heated to 240°- 250° and then quickly cooled down to preserve flavor and texture. It’s nearly impossible to quickly cool jars down after canning. Cooling too quickly can compromise the seal on the lid.
Additionally, heat alters the taste of milk and, depending on the fat content, can also make the milk gritty.
When it comes to canning cheese or cream cheese, you have an additional problem with the density of the product. It takes 60 minutes of pressure canning for the internal temperature of a pint of meat to reach an internal temperature of 250°. This is why we are advised to not can bananas, pureed squash and avocado: because the foods are so dense that it’s almost impossible to ensure that the inner temperature has reached 250° or more. (And also because the oil in avocado may prevent a good seal.)
Cheese and cream cheese are even denser than meat, so it will take even longer to get an inner temperature of 240° or more. This prolonged heat will also drastically alter the flavor and texture of the finished product.
Please read here what food experts say about canning dairy.
Exploding Canners
Exploding canners are almost always the result of not paying attention to the canner. An exploding pressure canner is usually caused by one of these things:
1-Clogged release vents. Solution: Clean the canner thoroughly after each use and inspect the vents to make sure there is no food obstructing it.
2-Too much pressure. Solution: Keep an eye on the pressure gauge and turn the heat down or up to keep the correct pressure.
3-Sudden temperature release. Solution: Inspect rubber gaskets and make sure they are properly seated. Replace any gasket that is brittle or cracked.
Do not use if the lid is dented or the locking flanges are bent.
Do not take the weight off the valve until the pressure is at zero.
Do not attempt a rapid cool-down by pouring cold water on the canner. In addition to the risk of the canner malfunctioning, the jars inside will not seal correctly if there is a rapid pressure reduction.
4-Low or no water. Solution: Follow canning directions and put the correct amount of water into the canner before starting the process and can for the correct amount of time.
“I’ve done this hundreds of times and no one got hurt.” This is the most common argument that Rebel Canners use for not following tested canning methods.
But as we all know, anecdote is not data. Testing kitchens (such as the USDA, state extension services or Newell/Jarden, makers of canning jars and lids) test these methods thousands of times, rigorously measuring and assessing the results. Home canners only can a few hundred times a year and rarely (if ever) test any of the results.
Every year there are about 1000 cases world wide of botulinum poisoning from home-canned foods. The highest percentage of these are in Italy, where home-canning is very popular. In the US there are about 40-45 cases a year. If one-third of the 350,000,000 people in the US eat home-canned food, that’s a 0.00004% risk. That’s pretty close to zero, right?
But it’s not completely zero. So you’ll have to decide. Do you trust the word of a home canner that something is safe or a testing kitchen that rigorously tests their results? Is 0.0004% safe enough for your family? (And keep in mind, these statistics that I have are from 2020, before the rebel-canner craze really took off.)
My advice: Don’t guess. Don’t take shortcuts. Don’t alter tested recipes. The more you follow tested guidelines, the closer you are to zero risk.
Isn’t pressure canning dangerous?
The Nervous Nelly may just be worried about the canning process itself. She thinks that pressure canners are mysterious and dangerous. The truth is, if you stay in the kitchen while your food is processing, there’s quite literally nothing dangerous about the process.
But what about all those exploding canners you always hear about? That’s because someone left the canner
unattended for an extended period of time or didn’t follow one of the safety rules. (See side bar for the reasons for exploding canners and how to prevent it from happening.)
Bottom line
Your family’s safety is in your hands. Of course, there is no food police to watch or control what you’re doing, so you are perfectly free to disregard or be as faithful to tested procedures as you wish.
But if you choose not to follow tested guidelines, please do not share that food with others outside of your immediate family. And if you post about it on social media, be sure to tell others that while you may not have had any problems with this process, there are no tests to ensure that it is safe.
That’s my advice.
If you pay attention to the principles of safe food preservation, canning is a great way to preserve food and stockpile your surplus for later use.
NEXT: Is canning really worth all the time and effort you put into it? Here’s my answer.
