Monday, 12 January 2014

11:33 – Costco run and dinner with Mary and Paul yesterday. The only things I picked up for myself were one 50 pound (22.7 kilo) bag each of white flour and sugar, another 170,000 calories worth of carbohydrates. Oddly, I wasn’t able to find any rice at Costco. As it turned out, that’s fine. As Barbara told me, we have two bags of rice in the pantry that I haven’t gotten around to repackaging yet. They’re fine for now in their heavy plastic bags.

I’m going to enjoy experimenting with 2-liter PET bottles and oxygen absorbers. Among common plastics, PET is by far the least permeable to air and moisture. You need something like ten times the thickness of PE or PP to match PET’s permeability. In the thickness used in soft-drink bottles, PET is slightly permeable, which is why carbonated drinks stored in PET bottles eventually go flat.

If I fill a 2-liter PET bottle with rice, perhaps 150 cc of air will remain in that bottle, in the interstices. Air is about 20% oxygen, which means there’s about 30 cc of oxygen in the bottle. If I also add a 300 cc oxygen absorber packet, it uses up 10% of its capacity reacting with that oxygen to form rust. That puts a partial vacuum in the bottle, so eventually (assuming no change in outside air pressure) about 30 cc of air will penetrate that bottle to equalize pressures. That 30 cc of air contains about 6 cc of oxygen, which the absorber will remove. That leaves a slight negative pressure in the bottle, which again will equilibrate against the outside air. Eventually, iteratively, the atmosphere inside the bottle becomes nearly 100% nitrogen (along with argon and some other minor inert gases) and the bottle is essentially nitrogen-packed. Much cheaper, easier, and much, much safer than nitrogen-packing from a compressed nitrogen bottle.