it was my first all grain, so I'm not expecting it to be perfect, for the mash volume, I went with 1 1/4 quart of water per pound of grain and 1/2 gallon per pound for sparge, I hit the pre boiling volume of 6.5 gallon. Wonder if because I have to split my wort in 2 to fit in my kettles the boil of volume was greater than if I've boiled it in one kettle... (BTW i have a bigger kettle coming in
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Yes, I would say that boiling in two kettles resulted in greater boil-off, due to two kettles likely having more surface area than a single bigger boil kettle.
When you get your new pot, do a "dry run" with just some water.
Measure out 5 gallons of cold water and bring it to boil for 60 minutes.
After the 60 minute boil, record the volume (while it's still close to boiling) to see how much you boiled off.
The volume will be 4% higher than it is when cold due to thermal expansion, so take that recorded volume and multiply it by .96. Five gallons minus your corrected final volume is your boil-off rate per hour.
Then cool the water off using your normal chilling method and then transfer it to your carboy or bucket using your normal transfer method. Then record the volume that actually went in to the fermentor. The difference between the corrected final volume and what is in the fermentor is your BK deadspace loss. Hops and hot/cold break will add somewhat to the deadspace volume, but not too much. You can always tweak your numbers after a real brew day.
Then transfer the water from your fermentor to a keg or your bottling bucket and record the amount of water left behind in the fermentor. That will be close to your fermentor losses (actual trub will add more losses).
So now that you know all that, you can calculate your pre-boil volume.
My brewery example:
I usually want 10 gallons of finished beer.
I lose 1/2 gallon per carboy during the fermentation process, so I need 11 gallons of cooled-off wort going into the fermentors (the "batch volume.")
I lose 1/2 gallon to my BK deadspace/pump/hoses, so I need 11.5 gallons of cooled-off wort.
To compensate for thermal expansion, 11.5 gallons of wort x 1.04 = 11.96 (let's call it "12 gallons") should be my target for a final post-boil pre-chilled volume.
I lose about 2.5 gallons in a 60-minute boil (yes, I have a really wide 25 gallon pot) so I need about 14 gallons of wort, pre-boil.
Thermal expansion from room temps to typical mashing temps is about 2%, so that 14 gallons of wort should be reading around 14.25 gallons at mashing temps. So 14.25 gallons is my target pre-boil volume.
I like to use 1.5 quarts of water per pound of grain whenever possible.
I also like to batch sparge and use 2 equal smaller volume sparges instead of 1 big sparge. You should expect to get about a 3% efficiency increase by doing a double sparge as opposed to a single sparge. Of course, it adds time to the brew day, but...eh.
