A long time ago in a galaxy far far away I got to screw around with LN dewars for waveguide pressurization and also extremely high power coax feedline pressuriz

A long time ago in a galaxy far far away I got to screw around with LN dewars for waveguide pressurization and also extremely high power coax feedline pressurization. You want about 2 or so PSI (varies by system) to keep water out and eliminate all chance of corrosion. The density of liq N2 is such that a small liq tank is the equivalent of a staggeringly large gas N2 pressurization system like the size of a tank car. Also its very hard to explode a liq tank and very easy to explode an ultra high pressure tank by making a mistake with regulators and pipes. A dewar would keep a feedline pressurized for, eh, maybe week, maybe weeks. Some dewars have a better or worse vacuum than others. Boys will be boys and we screwed around with the liq N2 a little. The author got ripped off because in bulk we paid roughly "milk" prices. Supposedly the liq N2 and milk price comparison held for decades at a time in the old days. So his little 20 liter dewar should have cost maybe $20 to fill. Then again, higher energy costs than the 90s, liability insurance, and "we know foodies will pay anything, so lets charge them anything..." Anyway. Although superficially it sounds shocking that a welding supplier would certify their product as food safe, all their gasses are designed for welding, like welding stainless steel food processing gear. So its safe enough to use anything they sell for industrial use, you'll be OK. If you think they're scared of giving you cooties, they're much more terrified of causing a dairy plant to loose its license. Its clean stuff. Also, they're terrified you or they will "cross the streams" with a O2 supply causing a huge explosion if there's any grease or oil contamination, so you can be absolutely sure nothing oily or burnable ever came near the gear, don't even worry about that class of contaminant. If you think about it, flooding something with N2 specifically to prevent chemical reactions means its not fit for sale unless its ridiculously pure. So it is. Another chemistry problem is you're looking for something that could end up in the product stream without being filtered out or destroyed by the process gear (or destroying the process gear), so kryptonite is kinda unlikely. Also it has to be liq at liq n2 temps because a gas would blow away and a solid (dirty ice, lets say) would remain stuck to the container. Good luck finding a substance like that. I'm pretty much out of chemistry ideas for a food contaminant.