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40l Keg Evaporation Rate?

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joecast

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lately ive been using the "standard" 10%/hour evaporatoin rate for my boils in promash to figure out how much to boil and what i will end up with. it seems though each time i end up with a lot less. i know i get a litre or two left in the keg when im done, but ive been about 3L short of what i should have.

ive got a 40L keg with the top cut off, and useing a three ring burner get a pretty good boil going. does anyone use a higher rate for evaporation? 15%? 20%?
joe
 

Guest Lurker

Big Dog Brewing
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I have an 80 l keg boiler (quite a wide opening) and a 4 ring burner. On one of my first brews I messed up the sparge calcs and ended up with way too much pre boil volume. So I did a 2.5 hr boil and took the opportunity to measure the volume through the boil.

I plotted the volume against time and found that:
1) a fixed loss per hour is a better fit than the Promash default of a % of the volume
2) for my boiler, at a vigorous rolling boil, the loss is 6.8 l/hour.
 

Doc

Doctor's Orders Brewing
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I use 10% and calulate my brews for 23.4 litres.
However when I do big beers that use a lot of hops (eg. Demon Ale, Arrogant Bastard clones), I still use 10% for boil off but calculate the brew for 25 litres as the extra hops soak up additional wort.

Beers,
Doc
 

JasonY

The Imperial Metric Brewery
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Personally I am going to adjust mine the other way .... more like 8% as my last brew was 6L over!! First brew using my converted keg.

Personally I would make sure you have your kettle losses due to deadspace as accurate as you can and then move on to figuring out evapouration. It is easy to measure the deadspace loss just with water but make sure your immersion chiller is in if you use one.

If you use a CFC make sure you include any losses in it as well.
 

dicko

Boston Bay Brewery
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Hi Joe,
As with most HB subjects there is allways varying views but for what it is worth I started using the percentage and found I was way out with my calcs.
I then used the obsevation of l/hr of boil and with my system I came up with 6 litres per hour.
This figure is fairly close for most boils but I have noted that I have lost as much as 6.5 litres on a couple and this I think is because I have had the burner turned up a bit more.
You will get the feel for your system and become very accurate with your calcs.
I hope this helps

Cheers
 

wedge

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Joe, mine sits pretty close to 14% nearlly all my brews. I agree with the others that literage per hours is better, as this wont change where as the percentage will change dependeding on the size of the batch,

ie, the size of your opening, and surface area of the liquid and heat of the boil, are the factors that determine how much you will loose. Increasing your literage i'm sure will not effect the evaporation of your boil. Hence using a percentage will work provided you dont change your batch size, while literage loss method will work all the time.
 

joecast

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thanks for the thoughts guys.
joe
 

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