I have had this conversations a couple times now. First of all, I would suggest that the calculations are guidelines to help give you a starting place. There are too many variables in every brewing system and brewer for any set of tools to precisely calculate anything.
Simply adjusting the amount of water to account for the absorption rate of whole leaf hops would alter the bitterness profile as well as the gravity. There is no way to account for how one handles the hops. Do you put them in a sack then let them drain into the wort? Do you whisk them out? No sack?
How precise are you measuring the final volume? I sit precisely 5.5 gallons or 5.4 or 5.6? A line on a carboy can be off by a lot.
Anyway, Beersmith does give you the ability to estimate the absorption based on your experience on your system and your process.
Select Tools/Water Needed.
You will need to know several values specific to your system:
- Lauter Tun Deadspace (sometimes called mash tun loss)
- Your kettle evaporation rate
** Losses to Trub and Chiller. This is where you enter your specifics from your experience of using whole hops on your system. Void of knowledge from experience, you can start conservatively and pick a number like 2oz water per 1oz of hops or test an ounce of whole hops in 150F water see how much they absorb.
