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Home Brew Forums > Home Brewing Beer > Beginners Beer Brewing Forum > Evaporation rate
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Old 01-07-2010, 02:58 AM   #1
mojotele
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Default Evaporation rate

So, in order to prepare for my next batch of beer, I decided to test out my evaporation rate. I filled my kettle with 3 gallons of water, put it on my outdoor burner, and cranked up the heat. Once it started to boil, I turned it down until it was just able to maintain a low boil. I boiled the water for 15 minutes, turned off the heat, then cooled it down in an ice bath for awhile until it was cool enough to handle. I measured 2.69 gallons.

That's a 41% evaporation rate. How the heck could it be that high? I've read all over the forums that it is normally along the lines of 10%-15%. Am I doing something wrong? I did leave the kettle uncovered the whole time, even when it was heating up. Should I leave it covered while it is heating?

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Old 01-07-2010, 03:18 AM   #2
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I think gallons/hour is a better way to think about boil off than percentage of volume boiled off. The amount that boils off is really a product of temperature, time and fluid:air surface area, total volume boiled doesn't seem to play as large an impact for reasons others can explain far better than I.

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Old 01-07-2010, 03:23 AM   #3
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I've read that argument on several other threads using the forum search, and I think I'm inclined to take that side as well. That would be 1.24 gallons per hour for me, which falls in line with some other people's numbers.

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Old 01-07-2010, 03:43 AM   #4
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Depending on how much juice I use on my system, I can get between 1-1.375 g boil off in 60 minutes. I think right around 1.2 is about ideal for me. I get a great boil, good hops utilization and can hit some high gravity beers with ease with that kind of boil off. Your number sounds good, but I would do a full volume boil for 60 minutes to make sure it is spot on. Your numbers will vary slightly between seasons, temps, wind factors, and humidity.

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