CHansen6

Recipes 

I too have always found the boil off in percentages rather odd at times. In the same pot a gallon of water will boil off just as fast if there are 5 gallons in it or 10 gallons. I've down sized a few recipes from 10 or 20 gallons to 5 gallons, and the collection values and the volumes came out odd a few times. I think it depends much more on equipment.

There might have been some sort of boil off perfect storm on my last brew. I lost close to 2 gallons in a little over an hour of boiling. There was a slow cooling process, so I would imagine I lost more than usual to evaporation. I found out after I was boiling that my roommates lent away the large plastic tub we have that I usually cool the pot in. Trying to cool a 30qt pot in the sink did not go well or fast. I had to top it back off, but it seemed to come out just fine, well despite it blowing the top off the fermenter.

skinfiddler

Recipes 

For three brews, (for whatever reason) my boil-off has been 7% short from Beersmith numbers. Next time I plan to increase their numbers by that much in the pre-boil volume.

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TexLaw

Recipes 

From my experience, you are better off fixed volume per unit time, rather than a percentage. It sounds like you boil about 1.2 gallons/hr.


TL

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jay075j

Recipes 

I've always just calculated mine at 1 gal per hour. It always seems to work out better by using a fixed volume rather than a percentage. IMHO of course.

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nathan

Recipes 

I have a decent idea where mine should be as the boil goes, up until I stick the immersion chiller in it. So I take note with 15 min left and if I need to, I crank up the flame, but I prefer a gentle "simmer" for my boils instead, as the wort darkens less. I'd rather end up a tad under volume and add boiled water I've got stored to get to volume, then aerate and pitch.

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blacklab

Recipes 

Exactly. The boiloff rate is related to the surface area of wort exposed to the environment, and the temp of the boil. A % implies that this will vary with volume, which it can't. Regardless of your volume, your boil off will remain constant in the vessel you are using, if you boil at a consistent temperature. My system is 7 gallons to 5.5 gallons @ ~212 every time.

EdWort

Recipes 

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.

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blacklab

Recipes 

showoff!

WBC

Recipes 

I don't think ED has a Blichmann and he is just pushing your button but .....
Did you buy one ED?

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chillHayze

Recipes 

I figure 3 gallons for boil-off, chill loss (contraction), and trub losses, so I usually boil 8-8.5 gallons (I am picky about not getting the break protiens in the fermentor). It is not really relative to initial boil volume as others have said. Pretty much flat rate for a normal batch.

No doubt there is a point where the curve swings rapidly, just not in the area us HBers are working.

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