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**tenbricks** · 05-11-2012, 09:50 PM

Quote:

Originally Posted by Bobby_M

Percent doesn't work for me. Boiloff is usually a fixed amount no matter how much liquid is in the same kettle. I lose about 1.5 gallons in 70 minutes in my keggle regardless if I start with 13 or 8 gallons.

This.

Boiloff rate is determined by (heat in) = (heat out), the temperature remaining a constant 212. In practice I think heat out is almost entirely the boiling (vaporization) of the wort, much less so by surface area/size/shape. Heat in is determined by rate of propane burning and how efficiently it's heating the kettle, which will be a constant regardless of boil size. Thus, mostly it will be constant amount per time, not constant percentage.

Quote:

Originally Posted by EdWort

The Blichmann Boilermaker 20 gallon kettle will boil off 2 gallons in 90 minutes. I'm attributing that to the larger diameter of the kettle compared to a keggle.

I have the same pot, and see a bit more than a gallon/hour for 5 or 10 gal batches. Must not have the propane as high up as EdWort does.

wailingguitar · 05-12-2012, 12:30 AM

Quote:

Originally Posted by Tankard

I'm tweaking the Beersmith settings and the default evaporation rate is 11%. So I would collect 7 gallons of wort and boil down to 5.5 gallons in an hour. That sounds a bit high. Has anyone ever calculated this based on a turkey fryer setup? I have a 30 qt aluminum pot.

Or, what do you have your Beersmith evaporation rate set at? How close is it, typically?

That is about what I am getting on mine (33qt tamale pot on a Bayou Classic)... about a gallon and a half (7 to 5.5) boiled off in an hour as opposed to a gallon (6.5 to 5.5) when done on the electric stove top. I have never used Beersmith or anything like that, so I have no idea about it's setup or defaults.

hausofstrauss · 11-08-2012, 05:23 PM

I would agree with the arguments for a volumetric boil off rate related to the surface area of the water rather than a percentage of total volume.

I also would think that environmental conditions would have an impact on that number too.

A hot dry day would allow more water loss, versus a hot humid day would absorb less.

If you are always working indoors and have a relatively constant temperature and humidity, you are in the best case scenario.