this post was submitted on 25 Jun 2026
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IANAMBBIHWITFAPI: I am not a microbiologist but I've worked in the food and pharma industries.
Botulin has a F0 time of 3 minutes, meaning that after 3 minutes at 121,1°C (250°F, ew) there is one in a bazillion chances that a spore may have survived. The toxins are easier to destroy, but if you don't destroy the spores, those will turn back into bacteria and produce more toxins, aside from potentially colonising YOU later.
Most industrial sterilisers have an in-pipe dwell time between 20 and 90 seconds, depending on how hot they get the product, given that F0 = 90 seconds @ 121°C is the same as F0 = 9 seconds @ 131,1°C, IIRC.
At least that's what I remember, I don't design these things, I just make them work.
You can't reach 121°C by boiling the cans on your stove top, because at 100°C water magically transforms into steam, the only way to prevent that is by adding pressure. Either you dive in the depths of the ocean, or you use a pressure system, like a pressure cooker... but with a standard cooker, how tf do you discern what's the temperature inside? You'd need at the very least a pressure gauge if you don't have a temperature probe (because since increasing pressure increases the boiling point, the current pressure gives you the current temperature).
You only need about 1 extra atmosphere of pressure for the boiling point of water to rise to 120°C, which is available at only 10 meters below the surface of the ocean. Even with a strong safety factor, 15 meters of water is well within the depths found in many large freshwater lakes, saltwater lakes, etc.
Alternatively, you can can things in a sugar syrup bath, which can easily reach the required temperatures. /s
(To be fully clear, this is an entirely terrible idea. The pressure within the cans will still rise to 2 atmospheres, and the result is very likely to be a can bomb spraying dangerously hot, and frightfully sticky sugar syrup all over anyone foolish enough to be close.)
Or a pressure canner 😜
Yeah I'm not privy to the art of home canning
I am a home canner. There are two processes.
Water bath canning, in which jars packed with food are boiled at ambient pressure and thus 100C or slightly less. This is only suitable for high-acid foods like fruit jams, jellies, acidic pickles and some tomato recipes, because the botulism spores are left alive, they have to be kept inert by the acid in the food. Any pot large enough to completely submerge the jars with an inch of water above will do; I use an old stock pot.
Pressure canning, in which jars are boiled in a pressurized vessel that raises the temperature high enough to kill the spores outright. This is the only method that can be used for low acid foods like vegetables packed in water, low acid tomato recipes, meats, soups etc. A pressure canner is conceptually similar to a pressure cooker, but larger to fit several jars, and they operate at higher pressures and temperatures. A pressure cooker is not suitable for pressure canning, a purpose built pressure canner is required.
Why not use oven?
A BUNCH of very good reasons.
Energy efficiency. Home canning is all about thrift. Heating glass jars with the hot air of an oven is less energy efficient than using a bath of water. Sure, it takes a wackton of energy to get the pot boiling in the first place, but once you've got it boiling you can do batch after batch after batch. When I'm done, I start a load of bath towels and pour in the (slightly cooled, no longer boiling) hot water. Because I paid for the water and the energy to heat it. With an oven, you open the door to take one batch out, all that heat comes spilling out.
It doesn't achieve higher temps inside the jar. Sure, you could put a canning jar in a 400 degree oven. Don't. But if you did, the water inside the jar would boil at 100C and get no hotter. So this wouldn't achieve anything more than water bath canning would. You don't want a rolling, bubbling boil inside the jar, that might push the liquid or solid contents of the jar out through the rim causing the seal to fail. Even if you did get the food sterilized, it would get recontaminated during storage.
High temperatures could damage the jars or lids. The lids, like all metal food packaging, has a plastic liner. Melting that onto my nice preserved food sounds like fun. For the sake of energy efficiency and thermal stress on the jars, the jars are typically preheated and packed with food still hot from cooking, but by the time you're ready to process them they may have cooled to, say, 60-70C? 140-160F or so? Putting them in a 400 degree oven might thermal shock and crack the glass.
Precise, foolproof, repeatable heating. I'm a 21st century suburbanite with a modern electric oven with digital thermostat, I STILL have to rotate a pizza halfway through baking because the back-left corner is the hottest. If you underheat a jar, you're gonna die of botulism this winter. Imagine trying it in some landlord special, or a 1950's Wife-O-Mat. Meanwhile, I can heat a batch of jars all to precisely 100C with nothing more sophisticated than a big pot full of water over a wood fire. Since I know the PRECISE temperature the jars are exposed to, I know EXACTLY how fast heat is soaking through them, and thus I know when the ENTIRE contents of the jar are heated to a safe temperature, and it works no matter what the weather is like.
For the same reasons mentioned above. Temperature isn't the problem. Without pressure the water turns into steams instead of boiling before it reaches a high enough temperature to kill the spores.
If you can't measure the internal temp, pretty sure you use brute force and let it sit for an extended period of time, so even if it doesn't hit 121/3min it at minimum got close for much longer.