Date: Fri, 10 Sep 2010 11:38:02 -0500
Reply-To: mcneely4@COX.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dave Mcneely <mcneely4@COX.NET>
Subject: Re: microwave oven
Content-Type: text/plain; charset=utf-8
Of course, the pressure cited by Alistair is gauge pressure at standard ambient atmospheric pressure (approximately sea level). Also, when using a pressure canner for sterilization (or for canning for that matter), the pressure must be gauged after all air has evacuated from the canner.
Bottom line, if you take this approach, be sure to obtain proper complete procedures from a qualified source. But yes, Alistair is correct.
So far as using a microwave for sterilization, my understanding is that surface sterilization of microwave compatible materials works, but that internal sterilization is more problematic because of uncertainty about penetration by the microwaves. This website from the University of Rochester briefly describes the use of microwave radiation for sterilization in a hospital setting (under the subheading "Methods)":
http://www.urmc.rochester.edu/Sterile/basics.cfm
I imagine that the original poster has proper procedures, provided by a qualified source, for using the microwave for his purposes.
DMc
---- Alistair Bell <albell@SHAW.CA> wrote:
> I do have experience and knowledge of steam sterilisation.
>
> To truly qualify in the game, the vessel needs to be able to contain
> 1 bar (14.7 psi) pressure, at that point temp. will be 121 C. If
> items to be sterilised are small, and I am guessing they are, then 20
> min at 121C and 1 bar, will sterilise.
>
> Timing started after temp and pressure at above values.
>
> Anything less than that is not sterilisation, sanitised maybe, but
> not sterilised.
>
> I am assuming that OP needs are for sterilising equipment rather than
> liquids etc. I have no data on the effectiveness of microwave ovens
> in sterilising equipment. Some talk about how they can be used to
> sanitise sponges etc. Obviously metal equipment can't be used in oven.
>
> If it was me that had this need, I'd spend the money on a pressure
> cooker with a gauge and internal rack, (with the supplies to be
> sterilised on rack above the water). I'd feel confident in this.
>
> alistair
>
>
>
> On 10-Sep-10, at 7:33 AM, Dave Mcneely wrote:
>
> I'm not certain that the device shown is meaningfully different from
> similar devices from the same manufacturer, but sold less expensively
> as "pressure canners." It includes an internal sterilizing rack, but
> that item is sold separately also. I had a colleague who taught
> workshops for high school teachers on laboratory microbiology
> practices. He taught them to use a Presto or All American (same
> company, essentially same equipment) pressure canner for
> sterilization (because an autoclave is such a large, expensive piece
> of equipment). I think instruction on how to use a pressure canner
> for sterilization can be gotten from other sources -- check with home
> health services for example. Here is the web site for Presto - All
> American. Of course, the consequences of the material not being
> sterile might be much greater for you than for high school students
> growing microbial cultures for class projects.
>
> http://www.pressurecooker-canner.com/prprca.html
>
> I also wonder if it would not be much more practical to just carry
> packaged and sterile stuff with you, but then I don't know and am not
> asking what you are sterilizing.
>
> David McNeely
>
> ---- David Beierl <dbeierl@ATTGLOBAL.NET> wrote:
> > At 08:42 PM 9/9/2010 -0700, Paul and Catherine Lemiuex wrote:
> >> We need to install a microwave oven in order to sterilize medical
> >> supplies so we can continue camping in our 1990 Westy. Having
> >> trouble finding a microwave that will work with a second battery and
> >> inverter. Does anyone have any experience, suggestions or comments?
> >
> > Running a microwave from Vanagon batteries would be tough. This
> > small 600-watt oven, for example
> > http://www.haieramerica.com/en/product/MWM6600RW uses 950 watts of
> > power. That means give or take one hundred amperes out of your
> > battery, and to support that kind of draw you should have 300 (for
> > AGM or gel batteries) or 400 (for conventional batteries) amp-hours
> > of battery capacity so as not to damage the batteries from too fast a
> > discharge.
> >
> > I think you'd be much better off looking into a steam sterilizer that
> > you can run off the stove. IIRC the stove burners are rated at 5600
> > BTU/hr each, which is the same or slightly larger than a regular
> > stove burner. A full propane tank should give you in the area of 48
> > hours burning time for one burner.
> >
> > Here's a ten-quart one at a not-too-outrageous price:
> > http://www.amazon.com/All-American-9-5-Quart-Pressure-Sterilizer/dp/
> > B000S8G1TS
> >
> > Yours,
> > DAvid
>
> --
> David McNeely
--
David McNeely
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