Author Topic: Calculating boil-off for new setup  (Read 748 times)

Offline kgs

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Calculating boil-off for new setup
« on: September 11, 2010, 06:10:57 PM »
Did my first outdoor brew last weekend (on a deck outside our kitchen). Being able to hose down my "kitchen" is a big plus. If I ever build a house, it will have a hose-down kitchen!

The issue that kept me hopping (no pun intended) was boil-off. It's a whole new setup for my brewing, a Bayou Classic SP10 and a 8-gallon kettle (intentionally small, because 4 gallons is about the largest I brew, and more often 3 gallons). I supplemented my kettle with water twice during the boil-off. In the end I hit my quantity and my numbers, but I'd like to get this more predictable.

Is it possible to get a better estimate of boil-off before my next batch by bringing water to a boil and then boiling it for a set period of time? The variables I thought might throw this off are a) the viscosity of wort vs. water and -- I'm guessing even more significantly -- b) the issue of how much propane to use. I suspect I had the boil too strong. It was fun to see that wort roiling, but I suspect that's not necessary.

K.G. Schneider
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Offline richardt

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Re: Calculating boil-off for new setup
« Reply #1 on: September 11, 2010, 07:27:07 PM »
I'll preface this with the statement that, "I'm not an engineer."
They'll likely be along later to give you the thermodynamic analysis.

But, I'll tell you this:  I, too, have a Banjo SP-10.  My perception is that it puts out a lot of energy.
I also suspects that the "rolling boil" it creates (even with a 10 gallon batch in a 20 gallon SS brew kettle) is incredibly impressive (and, perhaps, a little too vigorous!).  I've noticed SRM increases and (maybe more kettle melanoidins) especially with any decoctions done with the SP-10 burner at "full blast."  I'm definitely going to turn down the flow on the next few batches (both to conserve fuel, but also to keep from overdoing the boil).

More experienced brewers have suggested elsewhere that you should do decoctions and step mashing at lower temps (lower heat) settings on the burner.  You still accomplish the heating, but you prevent the scorching of the grains and keep the rolling boil in the boil kettle to a manageable level.


Offline euge

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Re: Calculating boil-off for new setup
« Reply #2 on: September 11, 2010, 10:03:41 PM »
You'll get a feel for it: vigor of the boil, time and ambient humidity all play a role. Plus, leave the lid 2/3 on and you'll get less evap, but increase risk of boil-over.

For me it's about 2 gallons a hour.
The first principle is that you must not fool yourself, and you are the easiest person to fool. -Richard P. Feynman