Modified Parti-glye Split batch

[Brewslikeaking]

I want to make 2 iPas like so:
Make a 7.5gallon batch of a DIPA (eg. A target of 8%abv). I want to split off 5 gallons of this to be a double ipa. As for the remaining 2.5gallons of wort - I wish to add 2.5gallons of water to bring it up to 5gallons and make a session ipa with it. My question is this; what can I expect the OG to be from the 2nd batch and how do I calculate it?

 

[lump42]

c1*v1= c2*v2
8% * 2.5 gal = c2 * 5 gal , solve for new concentration.
20 %(gal) = c2 * 5gal , simplify both sides
20 %(gal) / 5gal = c2 * 5gal / 5gal, divide both sides by new vol.
c2 = 4%

Works for any change of volume, boil-off or dilution. You can substitute abv for gravity, plato, or any solution concentration.

****Shortcut****
If you double the volume, you halve the concentration.
2.5 gal @ 8% = 5 gal @ 4%

 

[Jimbodaman]

http://braukaiser.com/documents/batch_sparge_simulator.xls

takes some practice getting used to but i find it to be very accurate

 

[Qhrumphf]

http://braukaiser.com/documents/batch_sparge_simulator.xls

takes some practice getting used to but i find it to be very accurate

You have to put correct info in, but yes, it's remarkably accurate.

 

[Brewslikeaking]

Brilliant thanks very much