Operating a Home Pressure Cooker
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Operating a Home Pressure Cooker
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The following is for sterilizing containers of glass, or metal. Do not place plastic items in a pressure cooker unless you want to end up with a gooey glob.
A home pressure cooker consists of these parts. Make sure that all of them are present and in good condition. All parts must be in good condition because once heated, the contents will be at high pressure. You don't want your pressure cooker to be a bomb!
- A Lid that has lugs built into its edge so that it can be screwed onto the pot.
- A release stem or nozzle that points up vertically in the lid. Make sure that this is not dented or damaged.
- A weight that sits on the release nozzle that is fitted into the lid. Weights come in many different shapes, and some have multiple settings. If there are several settings, you will use the one that says 15 (or 1 atm); if there is only one setting, it will be a "15" (or 1 atm).
- A rubber gasket, which is usually fitted into the edge of the lid. Make sure that this gasket is not cracked. If so, you will need to get a new one from a kitchen supply store. To assure yourself of getting the right size, take the top along with you when buying a new gasket.
- An emergency release plug, which is also in the lid.
- An interior support rack.
Before beginning, make sure that you have the right size pot (or correct size containers) so that everything will fit. Usually cookers of 8 quarts or larger accommodate bottles and multiple layers of things rather well. (For proper handling of various sorts of things needing sterilization, see the section further on.)
- Add approximately 1 inch (2 cm) of water into the pot. Then place the supporting rack in.
- Next add/stack the items you wish to sterilize into the pot. If you must sterilize things that should be dry, you will have to improvise with higher supporting racks.
- Affix the top to the pot, but do NOT place the weight on the steam release stem.
- Turn on the heat to high. Soon the water at the bottom of the pot will begin boiling and the water vapor will displace the air inside the unit. You want to expell all the air, so wait until a good jet of stem is spewing from the nozzle before going to the next step.
- Place the weight on the nozzle such that it is on 15 (1 atm). These weights are especially sized such that when the steam pressure inside the device reaches 15 psi (1 atm), it will be able to barely lift the weight and steam will escape.
- Start your 20 minute timer.
- Turn down the heat about halfway. You want the escaping steam to jiggle the weight so that about 10 hisses per minute are emitted. If you keep the heat too high, you will boil away all the water inside the pot and "burn" the pot. If no steam is escaping from under the weight, the pressure is too low, and sterilization will not be occurring.
- When the timer "dings", turn off the heat, and allow the device to remain sitting there. As it sits, it cools and the pressure slowly drops over the next 15 to 30 minutes. Do NOT remove the weight! Doing so when there is pressure inside will form a hot guyser that will coat your ceiling with all sorts of gooey stuff. And you will probably have widespread burns on your body!
- When you think that the pressure might be back to that of room pressure (ambient pressure), use a fork or spoon and very slightly lift the weight a millimeter - no more!. If you hear hissing, lower the weight back into place, and wait longer. If no hissing, then you may lift the weight off and set it aside.
- Carefully unscrew the lid and lift it off such that when you first start lifting it make sure that the rear edge of the lid lifts off the pot first. This makes the steam escape away from you. Of course, you may prefer having a face that looks like a blistered freshly boiled lobster, and hair that is in total disarray.
- If you have items inside that must be removed immediately - such as flasks of agar solutions that are going to be used to pour petri plates, you will have to cope with that situation without scalding yourself. Oven mitts usually work well as they protect your knuckles. Otherwise, it would be wise for you just to let the whole works cool off.
- Once you have emptied the pot of your supplies, dump the residual water into a sink, and leave the pot inverted to drain and dry. Once all the parts are dry, put the rack and weight into the pot and set (but not screw) the top in place. Put the device where it belongs - and do so in a way that does not damage the nozzle!
How to Sterilize Different Sorts of Things
- Liquids: best is in narrow-mouth screw-capped bottles. Next best is in narrow mouth containers that are covered with a double layer of aluminum foil such that the foil skirt hangs down at least two inches from the top. Make sure that the containers have at least three inches of free space above the meniscus. Actually, to be really safe, don't fill the containers more than half full. Set the containers in the pressure cooker, and make sure that all screw caps are loosened a full turn. This prevents the bottle from later exploding due to having superheated contents that suddenly become steam and BOOM!
- Empty GLASS petri dishes: these should have tops and bottoms put together, and they should be supported above the water in the bottom of the pot. After sterilization, they will come out moist. Moisture can be quickly eliminated by placing them in an oven at 220°F (105°C). Of course, you can also sterilize the glass plates in a 450°F oven for 45 minutes.
- Knives, spoons, spatulas: wrap them individually in paper towels. Don't use so much paper that you cannot feel the orientation of the item that is wrapped. After sterilization, you will tear off the handle end of the paper and slip the instrument out. In the pressure cooker, place these on a supporting rack above the water level.
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