It can be done. (The article is about energy savings thereby) I'd forgotten about the consequences of this graph. That line from the upper left, between the I and the Liquid shows how.
Some of us remember what happened when you left a full pop bottle outside in the winter. If you were lucky, it popped the cap and produced a pillar of frozen pop. If not so lucky, you had to pick broken glass out of the yard. Water expands when it freezes, so the pressure goes way up if you try to keep it confined. It'll just bulge a pop can, but if you use a nice strong cannister, the contents will partly freeze and partly not. That line I mentioned shows the temperature and pressure at which both ice (ice-I, to be picky about it) and water coexist. If your tomatoes happen to be the in the part that doesn't freeze, they get to stay freezer-cold without the unhappy side effects of water crystal growth shattering cells and generally munging up the texture.
Don't try this at home. If you eyeball the numbers on that graph, you'll see that to keep your goodies at -2C your cannister will have to stand of the order of 3000 pounds persquare inch, and at -20 30,000 psi. Even if your freezer survived the burst, opening the cannister too soon could be problematic. This seems to yours truly more of an industrial-scale job. Scuba tanks use about 1/4 inch of metal to hold 3000 psi, and the pressure here could easily go over that with a small temperature drop. I'd prefer the pressure tank to be below ground level.
This isn't new. Some places use this method to supercool food. When the pressure is released, the water in the food freezes, of course--but so quickly that the crystals are small, and less damaging. But you need strong systems to do it.
Isochoric means "constant volume." No, I didn't know that either.
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