Nahh, the explanation is there, alright, though nothing supports the "240 degrees" theory (I have to presume they would be Fahrenheit degrees, i.e. 116-120 Celsius, and of course glass can bear that alright):
>The whole industry switched to a new standard for the ripe California olive.
"It has to be heated to 240 degrees. And only a can would tolerate that, physically—you couldn’t do that with a glass jar."
Eventually, California olives came back. In cans.
Even if it was 240 Celsius (which I doubt), glass can bear it just fine.
Its the jar seal that's the problem. Space age plastics have no problem with 240F, 1920s I donno they had to use wax or natural rubber?
Edited to add, and the jar too.
The Ball Perfect Mason Jar was introduced in 1913 with a bead for the seal to rest upon. That would have been under patent and expensive in the 20s. So the tech (barely) existed to vacuum seal pressure cooked canned food in the 20s but it would have been patented and too expensive compared to cheaper cans.
Just take a second to think about that. 1913. The Romans could not have made such a jar. They lacked the material science. Things like this amaze me. A Ball jar is a simple item from my daily perspective. It is in reality a fairly advanced piece of material science.
So if you ever get flung back in time, probably your best best is evaporated sea salt. Then work your way up into simple cosmetics. You don't have the ability to create the supply chain necessary to create canning.
To be fair, Romans not only mastered glass manudacturing (which in itself pre-dates them), they more or less invented (or however the material was first made during their period) "transparent glass" and - more than that - they invented "pressed glass", i.e. they were among the first to be able to mass produce glass objects, by blowing glass into pre-made moulds, JFYI:
So, they would have been able to produce glass jars alright and would have probably used (like it was done for wine and amphorae ) "sealing wax" together with cork (and/or some resins):
Dunno if the Romans couldn't have made it (their glassware was startlingly good for what we imagine was possible then, if you do a simple image search) but pre-Pasteur, people wouldn't have have conceived of a vacuum seal formed by heat and pressure as a food preservation technique worth pursuing.
Nor could they have made a rubber for the seal. They didn't have access to the plants (Nazi's tried to use the only source that would have been available at the time to the Romans and failed [1]). Think of the supply chain required to get rubber plants from Asian or the Congo to a Roman city. Carthage would have had a hard time too.
Even if they had rubber in enough quantity, they'd have to vulcanize [2] it to make it work. That was years, centuries beyond them.
True, not out of rubber. But remember that air-blocking seals were important for the control of the fermentation process in wine production and preservation, and it's not beyond possible that they could have refined cruder pitch and resin based solutions if germ theory had been better understood then.
The setting point of jam is 105°C, so only very slightly cooler.
If I remember correctly from making jam with my mother, it's important to pour the really hot jam into the heated jars to ensure everything stays sterile -- so the jam going into the jars is around 105°C.
That's correct, but I've seen so many recipes on the internet that let the jam cool so the jars don't crack. That's ok for making a small amount to eat quickly, but for proper preservation you really need to do it hot.
It helps that my mother trained as a professional cook. That jam kept well for years.
I also remember it very clearly, as jam-making was by far the most dangerous cooking we ever did together. I could probably chart my maturity based on how much I was allowed to help, starting from washing the jars and putting them in the oven to sterilize, all the way to doing the whole process while she watched.
>The whole industry switched to a new standard for the ripe California olive.
"It has to be heated to 240 degrees. And only a can would tolerate that, physically—you couldn’t do that with a glass jar."
Eventually, California olives came back. In cans.
Even if it was 240 Celsius (which I doubt), glass can bear it just fine.