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"When you're high you never, ever want to come down"- Welcome to the Jungle, by Guns n' Roses

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He who controls the spice, controls the universe....

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"When you're high you never, ever want to come down"- Welcome to the Jungle, by Guns n' Roses

The temperature inside the jar while boiling will not exceed 100C, so even if the jar is well sealed, the pressure will not rise significantly.

In a pressure cooker, the temp, and therefore the pressure, both inside and outside the jar will be close to equal.

Since jars will never be hotter than the water they are in, 100c @ standard atmoshpheric pressure. Thus a sealed jar will not exceed 1 or 2 pounds pressure max while in open vessel of boiling water.

If Jars are inside a pressure cooker, same thing happens, but since pressure in cooker rises, the pressure difference inside jar verus outside of jar (inside of pressure cooker) is negligable. Actually I would believe it to become a negative pressure differance.

However, if pressure cooker were to suffer sudden pressure loss, by failure of seal, or submersion in cold water, you could have a problem. Since water in jar would be very hot >100c interenal jar pressure could become a problem. Thus it is wise to allow cooker and its contents to cool gradually.

Peace
/Gadget

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"When you're high you never, ever want to come down"- Welcome to the Jungle, by Guns n' Roses

Its non-pressurized, which is fine.

IMPORTANT that jar must not rest directly on bottom! Reason, bottom of kettle may exceed 100c (water can't cool it because bottom of jar is there) this will cause a tempature gradient, which will cause glass to expand, but only where the glass touches the hot metal bottom. Rest of glass (that touching water) will remain at 100c and no greater. If thermal expansion of glass is high enough it will create stress and crack the glass.

So, its important to place a wash cloth or something on the bottom to prevent glass touching metal. (or allow jar to float)

With regards to a sealed jar: Your vessel is not pressurized, there for your water will boil at 100c or less. the temp of the water (no mater how high the boil) will never exceed 100c. Thus the jar, and its contents will never exceed 100c. thus the internal pressure of the jar will only possible go up maybe 1 or 2 psi. Thus the sealed jar will be fine.

Now if your wondering why boiling water will never exceed 100c no matter how high you turn up the heat, try this. Any water molecule >100c will change state from liguid to gas, consequently if there is any liquid water, it MUST be @ or below 100c, otherwise it would be a gas (at standard temp/pressure)

Which brings up another important point regarding pressure cookers. The point being why it is important NOT to allow you pressure cooker to boil dry. Once all liquid water is gone, the temp will SKYROCKET really fast. If you have sealed jars inside this pressure cooker, the temp of the jars will skyrocket also. If those jars contain liquid water, it will try to turn into a gas, but since the jar is sealed ther is no place for the gas to go, thus the pressure inside the jar rapidly climbs till something gives (the lid, or the glass). SO its real important to not boil out all the water!

If it helps, I too was real worried about boiling sealed jars. That was untill I did the mental excersise on what would happen. I can still see my 9th grade chemistry teacher talking about temp/pressure stuff, and thats more than 15yrs ago! Funny how you remember things, I'm fairly certain she was wearing a plaid dress that day, short hair and mean as hell!

Peace
/Gadget

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"When you're high you never, ever want to come down"- Welcome to the Jungle, by Guns n' Roses

Have Fun
/Gadget