h a l f b a k e r y
Renovating the wheel
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
or get an account
If each compartment and drawer of a standard sized refrigerator could be sealed when closed and evacuated of most of its air, I think that the fridges' power consumption would be reduced, as food could be kept closer to room temperature while being preserved for even longer periods of time.
Phase diagram of water
[Basepair, May 28 2005]
||I have a feeling this would adversely affect most food and particularly fruit and vegetables.
||Quite right, [j999] - freezing under
vacuum is freeze-drying: the ice
sublimes to water vapour without going
through a liquid stage.
with the freezers in the restaurant is
just that they are quite big and have
good door-seals; when they close, the
warm room-air inside them is chilled
and contracts, causing a partial vacuum.
As far as I know, it's not done
||The ice sublimes to water vapor when it's freeze dried? Huh?
||Why would phase change take place in that direction during freezing?
||Partial pressures and equilibrium.
||I think that the basic idea--that a partial vacuum would allow food to be kept closer to room temperature--is way wrong. I cannot even figure out what led to that idea, unless it's some misunderstanding of freeze-drying, or possibly reducing oxidation.
As for preserving food, the comment by [xaviergisz] is probably understated. This would be a way of moving "freezer burn" down into the refrigerator. Dried-out bread, flabby lettuce, oozing tomatos, hard cheese--ick.
If reducing oxidation is the goal, try filling the fridge with nitrogen or something (now there's an idea).
||//that a partial vacuum would allow food to be kept closer to room temperature... I cannot even figure out what led to that idea...Dried-out bread, flabby lettuce, oozing sp:tomatoes, hard cheese--ick.//
||Funny you should mention cheese, it's vacuum packed when purchased, (at least at the grocers around here), this lack of air doesn't seem to make the cheese hard--ick, in fact it keeps the cheese from drying out and is where I got the idea for just evacuating the air from that one cubby in the fridge.
||Fruits would probably split open, so only certain sections of the fridge should vacuum pack.
||//Why would phase change take place
in that direction during freezing?//
It's not the freezing, it's the
vacuum. You can draw a 'phase
diagram' for water (or for anything, I
guess), with temperature on the
horizontal axis and pressure on the
vertical axis, and the diagram is divided
by lines into regions where the
substance is liquid, solid or gas. For
water, you can go from any state to any
other directly by a suitable change of
pressure and/or temperature. So, at
low temperature (anywhere between
about 0 and -80°C) you can go directly
from solid to vapour by reducing the
pressure. Carbon dioxide makes this
transition even at normal pressure
(hence dry ice), and is only liquid at
high pressures. Iodine is similar - solid
iodine makes a
beautiful purple vapour when
actually has many other solid states
(different forms of ice) which only occur
at higher pressures, so its phase
diagram is messy. See link.
||Also, closed containers may explode (unless fitted with a pressure equalising valve).