Consequences of a very high evaporation rate and/or boil off

[Geordan]

I recently assembled an "electrically assisted" 8 gallon kettle -- a 1500w element at full power, plus the stovetop burner at max result in a decent enough boil for my liking at 6+ gallons. I noted on its first run that the boil off was quite substantial: 1.5 gallons an hour (25% or so), versus the 13% of my smaller stainless kettle on the stovetop. I chalked this up to a more vigorous boil and larger kettle opening and went back to my life.

However, listening to an episode of Brew Strong last night, Jamil and Palmer both say quite emphatically that a boiloff/evaporation rate of higher than 15% will result in "bad things" in regards to melanoidan production. They say that "new brewers" (me) run with too vigorous a boil, and really just need a "gentle rolling boil" (paraphrasing). Taking this to heart, I'm running some tests, but it looks like I'm either at full power with stovetop and installed element and getting a decent boil at 1.5 gallons/hour evaporation rate, or I end up with a super wimpy 'boil' that doesn't seem like it will do much of anything.

Does anyone have any input on this subject? I tried searching but didn't see anything directly related to too high a boiloff rate resulting in negative effects on the wort.

NOTE: I have yet to actually brew in the kettle for a variety of reasons. All tests thusfar have been with water.

 

[Hammy71]

My system burns off a gallon every 1/2 hour. I've never noticed anything bad about my brews.

 

[photogscott]

As long as you're not boiling less than 60 minutes things will be fine

 

[Yooper]

Boiling off 1-1.5 gallons in an hour isn't really excessive. If you start with 6.5 gallons, and end up with 5 gallons, that's not that bad. Also consider that it's not really a % of boil off, as if you had a taller pot (but the same width) and started with 15 gallons, you'd still only boil off 1.5 gallons per hour. Does that make sense? Start with more wort, and you reduce the % of boil off while the actual amount remains the same.

Is your kettle 8 gallons? If so, that's sort of small and that does limit you. You could try using Fermcap in the boil to prevent boilovers and using more wort at the beginning.

 

[Geordan]

Thanks for your input everyone. Yooper, I'm glad to hear you mention a constant boiloff rate versus a percentage -- up until this point I had thought about my boiloff in absolute values (.75g/hr, 1.5g/hr etc) until listening to Brew Strong and hearing Jamil and Palmer talk about percentage.

To answer your question, the kettle is 8 gallons, which when I bought it seemed huge, and as I contemplate moving from 2.5 to 5 gallon batches starts looking smaller and smaller... I will definitely look at Fermcap. Would you mind expanding on the "using more wort at the beginning" statement? I'm not sure I grasp what you mean.

 

[Misplaced_Canuck]

I boil off about 2.75 gallons per hour. No problems here. I don't boil "real hard" either. Just a gentle rolling boil.

MC

 

[Yooper]

Thanks for your input everyone. Yooper, I'm glad to hear you mention a constant boiloff rate versus a percentage -- up until this point I had thought about my boiloff in absolute values (.75g/hr, 1.5g/hr etc) until listening to Brew Strong and hearing Jamil and Palmer talk about percentage.

To answer your question, the kettle is 8 gallons, which when I bought it seemed huge, and as I contemplate moving from 2.5 to 5 gallon batches starts looking smaller and smaller... I will definitely look at Fermcap. Would you mind expanding on the "using more wort at the beginning" statement? I'm not sure I grasp what you mean.

When you mash and sparge, if you start with more wort you'll end up with more wort. That's all I meant. If your batches end up with too little wort (4.5 gallons), start with .5 gallons more in the boil kettle by sparging another .5 gallons. That works will all but the smallest grain bills. A taller pot would help, since you're going to be limited to 6.5-6.75 gallon boils with an 8 gallon pot.

 

[Geordan]

Got it Yooper! I think I was just overcomplicating the statement in my head Makes sense now. I'm hoping to build a nicer and larger electric BK in the near future and relegate the existing 8 gallon to an HLT.

Misplaced_Canuck, thanks for the input -- glad to know it's not an issue for you either!