# Pressure canner physics

I have this pressure canner at home which unfortunately does not include a thermometer. The vessel has a volume of 18 liters. The procedure that I am following is this : pouring 3 litres of water inside it with the lid slightly open and waiting for the water to boil. After it boils I wait for around 10 minutes so that any air trapped inside the canner is squeezed out. Afterwards I close the lid. Can I assume that if I reach 1 bar pressure inside the pressure canner I will have 120 degrees Celsius inside it?

PS: I live at an altitude of around 700 meters.

• Does your canner have a "1 bar" setting? What brand is it? Jan 19, 2022 at 19:57
• @BowlOfRed Yes, it has a manometer. The brand is a belarusian, Novogas. Hope that helps. Jan 19, 2022 at 20:08

pouring 3 litres of water inside it with the lid slightly open and waiting for the water to boil.

Good. You definitely want to get everything up to local boiling. The amount of water is reasonable for many canners, but depends on the model and size.

After it boils I wait for around 10 minutes so that any air trapped inside the canner is squeezed out.

If you haven't closed the lid, this serves no purpose doesn't do anything about "squeezing out the air". However in many canning recipes there is a boil period with your jars in the water before the pressure phase. If you had room temperature food in the jar it can take a while to come up to temp. A 10 minute boil gets the food heated up so the (later) pressure cook phase doesn't have to last as long.

Afterwards I close the lid. Can I assume that if I reach 1 bar pressure inside the pressure canner I will have 120 degrees Celsius inside it?

The operating pressure indicated on a pressure cooker is the target additional pressure over your local atmospheric pressure that should be maintained during cooking. (The operating pressure may be lower than the maximum on the relief valve).

At 700m altitude, the ambient standard pressure is 930mbar (but can be lower with low pressure systems). Let's say on a rainy day that it's as low as 900mbar for you.

IF your cooker operates at a true 1 bar, then the internal pressure will be 900 + 1000 or 1900mbar (27.5 psi / 1.87 atm) absolute. Using a calculator you can find that water will be at 118.6C/245.5F when it is boiling under such pressure.

• I have a valve on the lid for pumping air inside the canner. I can close the lid and try to vent the air out of this valve by keeping it open, just like when you are venting air out of a bike tire. Maybe this will be better ? Jan 20, 2022 at 14:48
• @barcelona : you need the air in there for it to build up pressure. The only reason to do this would be if you needed to cook it at the standard boiling point for a while before you cooked it at the higher pressure. (Which would be better to do with the lid off, so you don’t risk fouling the valve)
– Joe
Jan 20, 2022 at 16:09
• I need to remove the air from the vessel so that the heat transfer if efficient. I will build up the pressure with the steam evaporating, after I close the Schrader valve. Jan 21, 2022 at 20:12
• That's not necessary, and if the lid is off, useless (air will just come back in wherever the lid is not fitting). The water is your heat transfer mechanism, not the vapor above. The quantity of water vapor in the vessel is independent of the quantity of air. Jan 22, 2022 at 4:44
• No, my heat transfer is done using the steam from the boiling water. Air is not to be present as it will create air pockets and transfer of energy will drastically slow. Jan 22, 2022 at 17:53