I've been taking a closer look at water calculations since I moved to all grain. I've been lazy with sparging, simply adding sparge water until I get what I want in the boil kettle. Of course, without letting the mash tun drain, I'm leaving a lot of sugar behind. Anyhow, I've read this post and have come up with the following example, which I plan to use until BS added the feature I think everyone is talking about. I'd love to get feedback, at least so I can ensure I understand the basic idea and calculations. Here's what I've come up with:
Grain:
12 lb grain
1.25 qts/lb
15 qt = 3.75 gallons for grain
Equipment:
space under screen = 2.25 gal (9 qt)
space which will not drain from mash tun .25 gal (1 qt)
Note: When calculating strike temperature, the "space under screen" + "gallons for grain" must be used.
So...
I actually need 3.75 gal + 2.25 gal = 6.0 gal in my mash tun to ensure 1.25 qt/gal of water is exposed to the grain. In addition, as noted above, 6 gal is used for strike temperature calculations.
For convenience sake, let's say I have 1.5 gal absorbed by the grain during mashing.
How much will I get from my mash tun?
6.00 gal starting
-0.25 gal which will not drain
-1.50 gal absorbed by grain
---------
4.25 gal from mash alone
I want 6.5 gal in my boil kettle, so I would sparge with 6.5 gal - 4.25 gal, or 2.25 gal.
Note: I didn't use the term "deadspace", as I don't understand if it means "space under screen" or "space which will not drain". If my understanding is correct, "space under screen" is used for strike temperature calculations and "space which will not drain" is used for sparge water calculations.
I think the new feature to be added would allow the setting of each of these.
Cheers,
redrover