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Old 09-09-2009, 02:29 AM   #1
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Default boil off rate of a keggle

Does anyone have a ballpark figure on the boiloff rate on a keggle over an hour?

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Old 09-09-2009, 02:57 AM   #2
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I would assume it would be around the standard rate - around 9%-15% per hour. Once the wort is boiling, the evaporation rate is based on the surface area exposed... although I'm sure the style of keg and size of opening would affect the rate slightly.

I'm curious... does gravity affect evaporation rate. It seems that higher gravity wort would boil at a higher temperature, meaning that water would turn into vapor more quickly. Any thoughts? (sorry to piggy back BeerPressure)

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Old 09-09-2009, 03:19 AM   #3
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I get just over 10% but I live in southern IL so the weather is usually humid

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Old 09-09-2009, 01:23 PM   #4
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I boil off about 1.5g per hour. 4500 Watt electric elment set to 80%

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Old 09-09-2009, 01:28 PM   #5
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Well, boil off cannot be calculated as a %... since it is a constant and %ages are not constants.

That being said, I boil off about 1.4 gallons per hour with 3800W of electricity going into my kettle. This was about what I got when I used an LP burner too.

Wind speed, humidity, surface area (though we are talking keggles so that is pretty standard here) and other factors will AFFECT the boil off rate, but not to a measurable degree on a HB scale


I start with say 7.5 gallons and boil off 1.4 per hour, so that is almost 19%, if you want to use a percentage... (but why???) And why is 9-15% standard?

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Old 09-09-2009, 01:48 PM   #6
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Pol, quit being difficult.

I'm sure he's just trying to work out some standard calculations or plug that number into some brewing software. You can use a percentage, but it's got to be over a specified time period. I think 10-15% evap over 1 hr is pretty standard with a nice rolling boil.

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Old 09-09-2009, 01:51 PM   #7
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I plug 11% into beersmith and it works out well for me.

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Old 09-09-2009, 01:51 PM   #8
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Quote:
Originally Posted by Lil' Sparky View Post
Pol, quit being difficult.

I'm sure he's just trying to work out some standard calculations or plug that number into some brewing software. You can use a percentage, but it's got to be over a specified time period. I think 10-15% evap over 1 hr is pretty standard with a nice rolling boil.
Untrue...

You will always boil off (within reason) the same amount per hour, as a constant. A % will change with volume. That is the whole story.

10% of 12 gallons is 1.2 gallons
10% of 6 gallons is .6 gallons

You dont boil off twice as much when you double your batch size.
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Old 09-09-2009, 02:00 PM   #9
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I agree with Pol again..sheesh. I boil off 1.5 gallons per hour running about 70kbtu. It's the same whether it's 6 gallons or 12.

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Old 09-09-2009, 02:54 PM   #10
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I said standard because almost any source that I have seen gives you somewhere in that range. I guess it is pretty much tied to batch size and should be stated that it is 9-15% for a ten gallon batch with a 60 min boil. And, a 60 min boil is (dare I say it...) pretty standard also. I guess it is more correct to state the boil-off amount as a volume/hr. Although, if you want to be picky, there are several conditions that will affect the boil-off rate including humidity, atmospheric pressure, temp of water and air, surface area and air movement around the vessel.

My original answer should have been:

The boil-off rate will be specific to your set-up. Develop some good measuring techniques and just do an experiment over a couple of brewing sessions. That way, you will know your specific boil-off rate.

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