Hello I did a test run with my 8 gallon brew pot today I feel it up too 7gal of water an boiled it for 90 min as you would if you boiling wort … Now my ? is after the 90mins I only had 4.5 to 4.8gallon left of water that work out to be round 2.5 to 3 gallon than boiled off now why would that be I did start out with my burner set too high was that the cause for this much loss ???
I suspect you are boiling way to hard. A good boil will loose 8 to 10 percent. After you hit a good hot break back it down till you see good wort movement but not heavy bubbling or wort jumping out at you. I am not sure but water may evaporate different then beer wort.
I think pot shape makes a difference, I too heard the 10% rule, but my brew pot boils off about twice that over an hour with a moderate boil. It’s not a tall skinny pot like a lot of turkey fryers, but more of a wide, short pot. I wouldn’t say it’s a problem, just account for it in your water volume calcs and you’ll be fine.
djt17 posted a formula in this thread to calculate boil off rate based on the diameter of the pot.
viewtopic.php?p=787926#p787926Someone else had different calculators on a web site. I can’t find it right now. I was thinking that it went down and he never rebuilt it.
boil off rate is determined by dia. of kettle and vigor of boil, humidity also effects boil off. for me on my keggle I figure for 1 gal per hour boil off. measure some water and put in your kettle and boil for 1 hour remeasure whats left and you will have a idea what your boil off will be.
on my 4 gal boils, I lose about 1 gallon. So, after malt syrup is included (half gallon in each brew) I end up adding about 1.5-2 gallons each brew. Now I am switching back to bottled water, I figure 6 gallons is all I need.
I hope to someday buy a 10 gallon pot. But for now I make darn good beer with my 5 gal pot that only cost $40 
