Evaporation Rates for Keggles

Hi
I have my evaporation rate set for 18.90%/hour.  Or, 2.54gallons/hour.  I have been using that for ages but am now wondering if it may be too high.

If you are using a converted keg as a boil kettle, would you share your evaporation setting with me?

Thanks

I get about 10%.  I have a rolling boil.  I don't do a vigorous violent boil.

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I set my equipment specs up a long time ago and simply left them alone.  My efficiency is about 68%.  I am now wondering if I am leaving too much in the kettle.

Does the time of year....winter/summer and humidity have anything to do with the boil off?

If you are achieving your fermentation volume and starting gravity, what is left in the kettle is no big deal.

As for evaporation rate, yes it does change based on the temperature at the surface of the liquid as pressure on the surface.  You should be able to calculate it using (mass loss rate)/(unit area) = (vapor pressure - ambient partial pressure)*sqrt( (molecular weight)/(2*pi*R*T) )  according to the Physics Department at the University of Ill.  I am pretty sure it is not enough to matter.  Most homebrewers are not exactly precise on liquid volumes.  A quart here or there doesn't matter.

jomebrew said:

If you are achieving your fermentation volume and starting gravity, what is left in the kettle is no big deal.......

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Thank you.  Therefore, if I use my Refractometer, adjusted for temperature, to monitor the gravity toward the end of the boil I will be fine.  I simply boil until I hit gravity.  But, I may screw up my hop utilization.  Any ideas for adjusting the coordination?