Figuring out boil-off rates

[BroomVikin]

I'd like to figure out the exact boil-off rate of my keggle but I have a question. If I fill it with a set amount of water, say 5 gallons, will it boil off at a different rate than if I fill it with 7 gallons? How about if it's filled with 7 gallons of wort? Do all those sugars affect the rate? All those thermodynamics are way above my pay grade.

 

[CGish]

What you are using for heat will make more of a difference than the volume in the kettle. On my E-BIAB keggle the setting on the controller is what dictates the boil-off. I use 65% for most boils, but I know the 75% number as well so I can reduce the volume a little quicker if I need to.

If you are using gas, hitting approximately the same BTU's each time will stabilize your numbers.

The volume in the kettle dictates how long it takes to reach the boiling point, but if the heat input is stable then the boil-off should be as well.

 

[BroomVikin]

I use gas. My typical MO is to open it up full throttle to reach a boil and then back it off to just high enough to keep the rolling boil going. I'd like to test it out with plan old water to figure out the rate but I wasn't sure if it would be pointless w/o doing a wort test.

 

[CGish]

No, not pointless. You may need to adjust a little, but the water will get you very close.

 

[BroomVikin]

Great, thanks. I'll give it a shot.