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Home Brew Forums > Home Brewing Beer > General Beer Discussion > Do barometric pressure changes affect boil temperatrue?
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Old 02-23-2011, 12:05 AM   #1
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Default Do barometric pressure changes affect boil temperatrue?

According to my nephew, yes it does.

He figured a rainy day 28-9 inches mercury, sunny day 30-1 inches mercury, so even a 1 inch change (1 inch of mercury approximately 0.5 psi) would change the boiling temperature nearly 2 deg. f. see this chart.

Yet another variable for the brewer?

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Old 02-23-2011, 12:10 AM   #2
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Your nephew is right.

Anyway, people have been boiling beer for centuries, without correcting barometric pressure, so, IMO, it's safe to say 2 or 3*C won't make much of a difference in your beer...

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Old 02-23-2011, 12:21 AM   #3
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[QUOTE]Yes. 212°F (or 100°C) is only at sea level, and 760 mmHg (I'll bet you learned this in high school chemistry and forgot).

As you go up in elevation, the atmospheric pressure drops. For example, in the "mile-high city", Denver, water will boil at 203°F (95°C). The water in an open pot will not get any hotter than this. So, for many things (vegetables), you would need to boil longer.

Of course, with weather changes, the barometric pressure changes and will also affect the temperature at which water will boil.

If you've used a pressure cooker, you might then know that under pressure water will boil at a much higher temperature.

Regarding brewing, the main reason for boiling is 1) drive off some unsavory compounds (DMS), and 2) isomerization of the hops (this is simply making the alpha acids soluble in the wort). I just found this. Might want to dig out the calculator. Maybe some kind soul here would plot this in Excel and post a jpg of the graph.


From Zymurgy Vol. 20 # 4 Special 1997.

Michael L. Hall writes in his article "What's Your IBU" that:

The isomeration reaction rate depends on temperature, so the boiling-point temperature at your elevation can make a big difference... Garetz* gives a correction factor for this effect:

Fbp = 1 / (1 + Eft / 27500)

where Fbp is the Boiling-Point Factor

and

where Eft is the elevation in feet.


* Garetz, Mark. Using Hops - The Complete Guide to Hops for the Craft Brewer, HopTech, 1994b.
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Old 02-23-2011, 04:19 AM   #4
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So, should brewers in Denver adjust their home brew recipes for the altitude?

It could also be a factor when calibrating your thermometer with 'boiling' water.

And every batch could be different. Do the pro's compensate for barometric fluctuations?

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Old 02-23-2011, 04:33 AM   #5
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Lets also remember that disolved solutes in water cause freezing point depression and boiling point elevation (this is the reason salting your driveway in the winter works). So i'm going to say no. Even the brewers in denver are probably boiling at 212 because of this.

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Old 02-23-2011, 05:47 PM   #6
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Here's a current barometric weather map for the USA.

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Old 02-23-2011, 06:04 PM   #7
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Quote:
Originally Posted by Hex View Post
So, should brewers in Denver adjust their home brew recipes for the altitude?

It could also be a factor when calibrating your thermometer with 'boiling' water.

And every batch could be different. Do the pro's compensate for barometric fluctuations?
Can't speak for the pro brewers, but I don't adjust for altitude in my recipes. I think that boil-off is the most important thing to consider, and that has a lot to do with your equipment, as well as altitude.

Quote:
Originally Posted by zepolmot View Post
Lets also remember that disolved solutes in water cause freezing point depression and boiling point elevation (this is the reason salting your driveway in the winter works). So i'm going to say no. Even the brewers in denver are probably boiling at 212 because of this.
No, we're not. 203 is just about typical boiling temperatures here in DEN. I grew up in the mountains at even higher elevations. Boiling temperature up there was sub-200 F. Frankly, as long as the boil temperature is above the isomerization temperature for alpha acid, and the boil is vigorous to drive off DMS, I don't think the actual temperature of the boiling liquid is that big of a deal.
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Old 02-23-2011, 06:12 PM   #8
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[quote=passedpawn;2671513]

Quote:

From Zymurgy Vol. 20 # 4 Special 1997.

Michael L. Hall writes in his article "What's Your IBU" that:

The isomeration reaction rate depends on temperature, so the boiling-point temperature at your elevation can make a big difference... Garetz* gives a correction factor for this effect:

Fbp = 1 / (1 + Eft / 27500)

where Fbp is the Boiling-Point Factor

and

where Eft is the elevation in feet.


* Garetz, Mark. Using Hops - The Complete Guide to Hops for the Craft Brewer, HopTech, 1994b.

Thanks for that, I never put it into numbers before but I have noticed that I had to add extra hops to get a well balanced beer.
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Old 02-24-2011, 05:16 PM   #9
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[quote=passedpawn;2671513]

Quote:
...Maybe some kind soul here would plot this in Excel and post a jpg of the graph.

From Zymurgy Vol. 20 # 4 Special 1997.

Michael L. Hall writes in his article "What's Your IBU" that:

The isomeration reaction rate depends on temperature, so the boiling-point temperature at your elevation can make a big difference... Garetz* gives a correction factor for this effect:

Fbp = 1 / (1 + Eft / 27500)

where Fbp is the Boiling-Point Factor

and

where Eft is the elevation in feet.


* Garetz, Mark. Using Hops - The Complete Guide to Hops for the Craft Brewer, HopTech, 1994b.
Can someone rewrite this formula in terms of boil temp vs. hops isso?

Other factors including water profile are not necessary in delta boil if you take an actual reading each boil, and compensate, but by what percent? Longer boils in Denver on a rainy day? to short boils in the summer in Death Valley?.
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Old 02-24-2011, 07:23 PM   #10
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I do not see how it would matter. Sure the boiling temp would fluctuate a little but who cares? We are not brewing beer at boiling temps anyway. Since I live at 8000 ft, my boiling temp is 197, but I still mash my ales between 152 and 158. I mash out and sparge at 180 so the boiling temp plays no part here.

As far as the boil, as said above one's own equipment plays more of a factor then actual boil temp. Even through one may think I would lose less moisture in the boiloff with my 197f boiling point, the lower atmospheric pressure also lowers the vapor pressure. So the water content will liberated into steam easier. I find if I do a really vigorous boil, I can lose over 2.5 gallons in a hour!

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