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Home Brew Forums > Home Brewing Beer > General Techniques > Canning Wort - How To Measure Pressure Cooker Temp
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Old 12-25-2011, 04:37 PM   #1
alfista
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Default Canning Wort - How To Measure Pressure Cooker Temp

Merry Xmas All,

I was thinking of trying to can some wort for future starters.

I have a pressure cooker, but it doesn't have a temperature gauge on it. It only has a pressure relief valve. What is the best way to tell if I've reach a temp long enough to fully sterilize the wort in the mason jars?

Thanks!

Jason

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Old 12-25-2011, 04:58 PM   #2
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My cooker has a pressure gauge, but generally if the weight on top is spinning around it is at the proper temperature.

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Old 12-25-2011, 05:25 PM   #3
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The pressure determines the temp.
You CANNOT heat liquid water past boiling. Thats why you use the pressure cooker to raise the temp of boiling water.
I am sure there are tables around somewhere that give pressure/temp but most guidelines are X psi for X amount of time
So if you have steam escaping it is at temp.

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Old 12-25-2011, 06:01 PM   #4
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Mine has a red tab that pops up when it's up to temperature.

Pressure canning wort has been one of the biggest time savers in this hobby. The cat hides under the bed, though, when the little weight hops and hisses.

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Old 12-25-2011, 06:07 PM   #5
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The 15 pound 'weight' is equal to about 250F. You can look up the others on line.

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Old 12-25-2011, 07:54 PM   #6
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PV=nRT

This represents (among other things) the relationship between pressure and temperature. If you assume volume is a constant (the sealed canner) and just ignore the 'nR' bit, it's obvious that if you raise 'P' that 'T' will also go up. It will go up just as high as 'P' goes, unless some other part of the equation changes. The point where 'V' changes is determined by how heavy the vent weight is. When the pressure inside the canner becomes great enough to raise the weight on the vent, that will directly determine how high the temperature can go, i.e., all home canners I've seen regulate the temperature by regulating the pressure. Simple, and provides an automatic safety backup to the design, even though pressure cookers & canners are also provided with safety blowout plugs, too.

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Old 12-25-2011, 08:52 PM   #7
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Just Google "Saturated Steam Tables". i.e. 212F = 1 ATM (14.7 psia) or 50 psig (64.7 psia) = 298F. You can use a linear relationship (accurately enough) to get a decent idea of your temp vs pressure if you don't want to use tables.

EDIT: 14.7 psia = 0 psig and http://www.indpipe.com/images/PDF/st...sure_table.pdf the link will take you to a quick steam table. And you really only need to be above 212F for 15 minutes to ensure sterilization.

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Old 12-26-2011, 04:31 PM   #8
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Quote:
Originally Posted by TheWall View Post
Just Google "Saturated Steam Tables". i.e. 212F = 1 ATM (14.7 psia) or 50 psig (64.7 psia) = 298F. You can use a linear relationship (accurately enough) to get a decent idea of your temp vs pressure if you don't want to use tables.

EDIT: 14.7 psia = 0 psig and http://www.indpipe.com/images/PDF/st...sure_table.pdf the link will take you to a quick steam table. And you really only need to be above 212F for 15 minutes to ensure sterilization.
Actually, you need to be at 250F for at least 20 minutes (depending on the size of the container). Above 212F for 15 minutes is obviously better than regular boiled, but is not STERILIZED. If you are talking about pint jars you need 20 minutes, and if you are talking about quart jars you should be using at least 25-30 minutes.
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