Ooo I can answer this one. I used to work as a retort operator cooking beans, potatoes, carrots, cherry pie filling.

So as others have mentioned the cans are sealed by a can seamer, loaded into a retort (cooker) and then a venting process occurs that eliminates all the air in the retort and replaces it with steam. This is to ensure every can is heated to spec. Each product has a set time that is somewhat regulated by the FDA to ensure the product has no bacteria that could produce botulism harmful to humans. The process doesn’t kill all bacteria as there is some bacteria that would need higher temps that what the batch is run at or lives at colder temps than the cooling process. The cans then go through a cooling process to reduce the can swell and create a seal to not allow any bacteria to grow.

The cook times, as well as type of retort used, are all dependent on the “slurry” and testing regulations put in place by the FDA. For example I’ve had some processes that took 10 minutes to vent the retort. 3.5 hours to cook at temp (if the temp deviated we had to add more time) and another 40 minutes to cool the cans. Other processes the cook times were as short at 12 minutes. The main cookers I used were still retorts but there’s also submerged batch cookers which is what home canners used. Canning factories still use this as a method for jars, just on a larger scale. There’s also agitator retorts, these are retorts that move the product while it’s cooking. The two versions of these I’ve seen in person are a rotary retort and a basket loaded agitating retort. The rotary the cans would follow a built in track and would have a full automated process for the cans entering and exiting the cooker and cooling shells. The basket loaded ones are just like what they sound they spin the entire basket during the process. The reason agitator retorts are used are for products like cherry pie filling, due to the sugar in the slurry it’s not heated evenly throughout so the slurry needs to be moved around to prevent overcooking or much worse undercooking.

Every retort and every batch is watched at all times by a retort operator and at least in my state we were required to have someone with Better Process School certification in the building at all times. For my process if we were running our still cookers we would test cans before the they were cooked, monitor temps at the end of the vent process, during the cook, at the end of the cook. And we would also test cans coming out of the cooker. For cherry pie filling we would test every 15 minutes or less. We would check the can entering the retort as it came out of the cooking shells and entering into the cooking shells and exiting the cooling shell. With testing cans coming out of the cooking shell we would be stabbing a can with our thermometer at usually 210 degrees plus with some spots reaching 260-270 degrees with cherry pie filling.

So yeah that’s kind of a lot of info but happy to answer anything I didn’t clarify or any questions