[pct-l] Dehydrating/Freeze dried

[Jennifer Zimmerman]

Yes, it works by sublimation - transition directly from solid to gas state,
just like dry ice.  At a low enough pressure (below the triple point, where
all three phases exist in equilibrium) water will sublimate.  In general,
the lower the ambient pressure the "easier" it is to turn water from a
liquid to a gas. So if you had a dehydrator that worked under vacuum you
would get more efficient drying with less heat applied.  Freeze-drying is
this concept taken to an extreme.  Please note that I am by no means a
fluid engineer so I'm sure the above is not 100% accurate.

This can also happen in really cold temperatures with extremely low
humidity, like Chuck and Ed mentioned with the home freezer. Our winters in
the great white North are good for this - you can hang a wet shirt outside
when it's -20F and it will dry itself.  I prefer to use the dryer though.

Tomorrow's the big day for us!  After four years of thinking about the
trail every freaking day, I finally get to start hiking!

JZ


On Thu, Apr 18, 2013 at 7:39 PM, Ed Jarrett <edjarrett at msn.com> wrote:

> No heat is involved.  Commercially it is done by flash freezing and then
> subjecting to a vacuum.  At home you just let the freezer suck out any
> moisture over time.
>
> Ed Jarrett Blog: http://aclayjar.blogspot.com/  Twitter:
> https://twitter.com/EdJarrett53 Facebook:
> https://www.facebook.com/ed.jarrett.71
>
> > From: diane at santabarbarahikes.com
> > Date: Thu, 18 Apr 2013 17:27:42 -0700
> > To: pct-l at backcountry.net
> > Subject: Re: [pct-l] Dehydrating/Freeze dried
> >
> > I think I read somewhere that it is frozen, then heated to stimulate
> > the release of water, then frozen again etc etc. They do this very
> > quickly using a heated surface and extremely low temperatures.
> >
> > On Apr 18, 2013, at 10:00 AM, pct-l-request at backcountry.net wrote:
> >
> > > From: surferskir at aol.com
> > > Subject: [pct-l] Dehydrating/Freeze dried
> > > To: pct-l at backcountry.net
> > >
> > >
> > > I am an avid at-home dehydrator.  I love taking different dried
> > > foods on the trail.
> > > However, many of the things that I see in the sporting stores are
> > > 'FREEZE DRIED".
> > >
> > > How do they freeze dry foods?  What is the process(es)?  Is it
> > > something that one could do at home?
> > >
> > > --Dennis--
> >
> > _______________________________________________
> > Pct-L mailing list
> > Pct-L at backcountry.net
> > To unsubscribe, or change options visit:
> > http://mailman.backcountry.net/mailman/listinfo/pct-l
> >
> > List Archives:
> > http://mailman.backcountry.net/pipermail/pct-l/
> > All content is copyrighted by the respective authors.
> > Reproduction is prohibited without express permission.
>
> _______________________________________________
> Pct-L mailing list
> Pct-L at backcountry.net
> To unsubscribe, or change options visit:
> http://mailman.backcountry.net/mailman/listinfo/pct-l
>
> List Archives:
> http://mailman.backcountry.net/pipermail/pct-l/
> All content is copyrighted by the respective authors.
> Reproduction is prohibited without express permission.
>