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DIY autoclave? Ideas? Answered

Does anyone know of a way to build an autoclave? I know that they are essentially pressure cookers on steroids, but would a standard pressure cooker truly sterilize something? No, I'm not trying to give myself tattoos or attempt surgery on the cat. It would be mostly for biology experiments, such as swabbing cultures. I could get one on eBay for about $150 minimum, but I don't really feel like spending $150 to grow bacteria. Any ideas?

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jimwig (author)2011-10-03

a fella named magpie did some work on a homemade autoclave here:

http://www.sciencemadness.org/talk/viewthread.php?tid=14652#pid190003

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bkf11 (author)2010-01-26

OK, old thread but I'll add what I know. I work in a biology lab and we frequently use normal pressure cookers to sterilise culture media. We put 2cm water in the bottom, have a little shelf that things sit on above the water, put in the items to be sterilised, leaving bottle tops open a bit. Shut lid and heat on a stove top till it's boiling, then put a 15 (PSI?) pressure regulator weight onto the vent and heat till steam is coming out (noisy). Then cook for 15 minutes and let cool. Done

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westfw (author)2009-06-26

For "typical" biology experiments, I suspect a pressure cooker will work just fine. (It's good enough for canning foods for human consumption, right? You're not going to have so many of those high-temp extremeophile germs around your home experiments, probably.) Pressure cookers have a vent, so the air goes out and they ARE full of steam. Sterilizing is one of their primary functions (canning), although "modern" usage night focus on cooking things faster.

Asian markets frequently sell agar powder and/or "sticks." Also available from "natural food" suppliers.

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lemonie (author)2007-08-09
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lemonie (author)CameronSS2007-08-10

Well it's bad-eyes, laziness, or intoxication, take your pick... Sorry L

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lemonie (author)bumpus2009-06-25
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NeroInferno (author)2009-06-25

A friend of me built 2 pressure cookers that can reach 60psi using 2 old beer barrels. They are built to keep a pressure of 60psi. He semply cutted them on the top to make the part of the lid and the part where you put things to sterilize. Then he used some wing nuts to close the pressure cooker. The pressure cooker can reach all that pressure but he use them at 21-25 psi. Once it went to 35psi and melted all the plastic of the autoclavable bags. Imho if you dont sterilize a lot of thing a common All American Pressure Cooker will work. Please contact me privately at info@bemushroomed.com thanks! Fabio

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tersmurf (author)2008-07-19

What about a rice cooker. It has a top cover and is electric heated. It steams water and steam comes out the top.

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ben.g (author)2008-02-08

Microbiology protocols will tell you 121 deg steam is the minimum temp for sterile technique.

This site has the vapor pressure for 120 deg steam as being around 1500 mm Hg.

To convert that to psi, we have normal atmospheric pressure ~15 psi, and then an additional 15 psi that we might be able to get from a nice pressure cooker.

30 psi = 1551 mmHg so we could use a decent pressure cooker as a sterilizer, however,

hot air does not sterilize like steam. So, you have to make sure that the pressure cooker ejects enough air that the entire surface of the cooker is covered in steam. An easy way to test this would be with some autoclave tape

And if you were feeling really salty, try welding together a water heater with a 15 psi release valve. Be careful! Biology can be dangerous.

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ll.13 (author)2007-08-10

Excuse me, but why, when sterilizing, is it under pressure? I thought just boiling water for a few minutes would do it. Pressure cookers do have the weights on top for adjusting the pressure to build up, that's about all I know in this kind of thing. :/

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NachoMahma (author)ll.132007-08-10

. To improve the kill ratio and speed up the process. Boiling water does a pretty good job of "sterilizing" baby bottles, etc, - you can be reasonably sure of killing enough germs to prevent sickness.

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ll.13 (author)NachoMahma2007-08-11

Oh, ok. On a pressure cooker it gets enough pressure to throw all the contents out, and the pressure cooker we have has the weight range of 5, 10, and 15 lbs. for different pressure, which I guess means 15 p.s.i. for the biggest.

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CameronSS (author)ll.132007-08-10

As has been discussed, the pressure raises the boiling point of the water.

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mcflyalright (author)2007-08-09

you can get agar gel from a hobby mushroom growing supplier. under a heading like substrates or liquid culture.

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NachoMahma (author)mcflyalright2007-08-09

. I'd be suspicious of fungi-/horti-/agri- cultural grade agar. Liable to have contaminants that will affect the cultures. Maybe not, but I'd check real close.

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NachoMahma (author)2007-08-08

. IIRC, the main reason an autoclave is pressurized is to raise the boiling point of the water, so the autoclave runs hotter. We used a pressure cooker/hot plate for an autoclave, at an animal shelter I worked for, during spay/neuter days.

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NachoMahma (author)NachoMahma2007-08-08

. There's a real good article on Wikipedia - http://en.wikipedia.org/wiki/Autoclave
. Even has a few pics of "stove-top autovclaves" that look a lot like what I used.
. From the same page: "However, in 2003 scientists discovered a single-celled organism, Strain 121, that survives traditional autoclave temperatures.[2] Prions, like those associated with Creutzfeldt-Jakob disease, also may not be destroyed by autoclaving." Yikes!

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CameronSS (author)NachoMahma2007-08-08

Yeah, I read the Wikipedia article before I posted he topic. So what would actually be required to produce autoclave temperatures? Would a pressure cooker actually sterilize?

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NachoMahma (author)CameronSS2007-08-08

. It only has to get a little above 100degC for about an hour. IIRC, on the one I used, the pressure relief weight said "5" on it - not sure if that was PSIG or what.

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CameronSS (author)NachoMahma2007-08-08

So I should be looking for cheap pressure cookers? Also, since you seem to be intelligent (regarding this topic, at least :-)), do you know of a good place to get agar gel?

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NachoMahma (author)CameronSS2007-08-08

> So I should be looking for cheap pressure cookers? . I would. As far as I can tell, a "professional" autoclave is just a pressure cooker with bells and whistles. The main diffs being a more convenient water reservoir (sometimes automatic), "shelves" for the sterilizees, and a timer. . > since you seem to be intelligent (regarding this topic, at least :-)) . Not so much intelligent, just lots of experience (at least compared to most ppl on this site). If I hadn't worked at the animal shelter, I probably wouldn't know squat about autoclaves. . The more I learn, the more I realize just how ignorant I really am. . > do you know of a good place to get agar gel? . Haven't the slightest idea. One of the many things I have no experience with. IIRC, it is just a generic growth medium (similar to gelatin, to a layman such as I) - should be readily available on the Web.

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NachoMahma (author)NachoMahma2007-08-08

. Actually, it only has to get hot enough to boil the water in the "germs."

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