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xhooliganx
Munky


Registered: 03/09/06
Posts: 900
Loc: reno, nevada
Last seen: 2 years, 8 months
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what's the difference between a sterilizer and a pressure cooker?
#5455967 - 03/29/06 05:21 PM (17 years, 9 months ago) |
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I'm still kinda confused about what the difference is. Why do the AA sterilizers cost so much more? What kinda benifits would there be to having a sterilizer over a pressure cooker?
L?K
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mogur
regnartS

Registered: 11/15/05
Posts: 322
Loc: Puget Sound
Last seen: 11 years, 2 months
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Re: what's the difference between a sterilizer and a pressure cooker? [Re: xhooliganx]
#5456018 - 03/29/06 05:36 PM (17 years, 9 months ago) |
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The equipment that most mushroom cultivators buy from AA are pressure cookers that are used for sterilization. The equipment used in laboratories for medical and microbiological work are called autoclaves. They differ from pressure cookers/canners in several ways. They clear the pressure chamber of trapped dry air, by either pumping steam through it or using an initial vacuum. Dry air pockets interfere with sterilization because they can insulate the objects to be sterilized from the moist, high heat. Growers that use cookers for sterilization, try to clear the dry air pockets by allowing the steam to vent thoroughly before building up pressure. Autoclaves are designed to do that more reliably.
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FooMan



Registered: 02/02/05
Posts: 8,957
Loc: Earth
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Re: what's the difference between a sterilizer and a pressure cooker? [Re: mogur]
#5456135 - 03/29/06 06:00 PM (17 years, 9 months ago) |
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Good explanation!
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Quick WBS Prep
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sever
Where am I?
Registered: 02/02/03
Posts: 161
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Re: what's the difference between a sterilizer and a pressure cooker? [Re: mogur]
#5456872 - 03/29/06 08:07 PM (17 years, 9 months ago) |
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~
Edited by sever (07/17/06 02:28 PM)
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mogur
regnartS

Registered: 11/15/05
Posts: 322
Loc: Puget Sound
Last seen: 11 years, 2 months
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Re: what's the difference between a sterilizer and a pressure cooker? [Re: sever]
#5463261 - 03/31/06 09:23 AM (17 years, 9 months ago) |
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Quote:
sever said: steam builds up in a PC... there are no dry air pockets. .
Don't make me get my flying monkeys.
Quote:
Effective moist-heat sterilization depends on having saturated steam conditions. When air is present in the system to be sterilized, saturated steam temperature and pressure conditions no longer apply.
The air dilutes the steam and a lower temperature than expected is imposed at a given pressure. Trapped pockets of pure air completely prevent steam contact and provide dry-heat sterilization conditions. With saturated steam, one log of kill occurs at 121.1?C for one minute. Lower temperature necessitates much longer times to achieve each Fo. Dry-heat sterilization conditions require much higher temperatures and greater time to create one log of kill.
Two methods often are used for eliminating air: Pre-vacuum cycles. Autoclaves commonly rely on a vacuum pump to eliminate air from the piping, tubing, equipment, clothing, gauze packing and chamber prior to introducing steam. A cycle of vacuum pull followed by a steam charge is often called a ?prevac.? A series of three prevacs usually suffices to remove air, as long as there are no major leaks. The advantage of prevac cycles is that they can remove air from more-porous materials and potentially deeper ?deadlegs.? The disadvantage is that a vacuum pump has to be purchased and maintained.
Steam turbulence and flow. When nothing is present that will trap air, vacuum cycles are unnecessary. Many autoclave loads and most fermenters and piping systems can be sterilized using a ?gravity cycle.? This method depends upon steam flowing throughout the system in a directional way to ensure air is swept out of the system. Steam flows from points of introduction to steam traps, orifices or through valves that allow the air, condensate and steam to leave the system. The piping is designed with minimal pockets or deadlegs to trap air.
One technique to eliminate air from a stagnant area is to introduce steam in a way that disrupts the air and then sweeps it out of the system. The most common place to trap air is at a high point that is not vented through a trap or orifice. In fermentation, for instance, it is important to ensure the nozzles at the top of the tank, where the agitator seal and other ports exist, do not trap air. Sending steam in through the nozzle is one method to eliminate air. Designing so that steam flows out through a nozzle to a trap is another. A third method is to introduce steam from another port and point it toward the nozzle suspected of trapping air. The steam will create turbulence and disperse the air. Steam flow through the rest of the system (if designed correctly) will carry the air out.
Systems that require sterilization can become pretty complex, especially when piping systems must be included. So, during design, visualizing steam flow and sequencing automatic valves to direct steam flow in defined flow patterns is an important check. Also, choose valves, such as diaphragm ones, that do not have pockets that trap air.
The advantage of using steam turbulence and flow is that no vacuum pump is needed. The disadvantage is that more design skill is required to ensure proper flow of steam.
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sever
Where am I?
Registered: 02/02/03
Posts: 161
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Re: what's the difference between a sterilizer and a pressure cooker? [Re: mogur]
#5466791 - 04/01/06 08:42 AM (17 years, 9 months ago) |
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Edited by sever (07/17/06 02:27 PM)
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mogur
regnartS

Registered: 11/15/05
Posts: 322
Loc: Puget Sound
Last seen: 11 years, 2 months
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Re: what's the difference between a sterilizer and a pressure cooker? [Re: sever]
#5466953 - 04/01/06 10:03 AM (17 years, 9 months ago) |
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Porkchops don't trap much air, so there isn't too much problem with them, if the cooker is vented for a few minutes before pressurizing. But when you try to sterilize instruments wrapped in foil, stacked bags of spawn, and jars of grain that are half full of air, autoclaves do a better job than cookers. That's all I was trying to say in response to xhooliganx's question about the difference between a PC and a sterilizer.
Labs rarely autoclave for more than 15 or 20 minutes. You won't find many mycologists that PC for less than an hour. The reason is dry air. If you use a wet oven mitt, you will quickly notice how well heat is transmitted through the damp cloth. It just takes longer for the heat to get to the center of a jar of grain full of (relatively) dry air, as opposed to say a jar of liquid culture that can quickly absorb the high temps in a PC.
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