After using the GrainFather for a little while I realized that I instead of wasting a lot of time waiting for things to heat up (ramp-times) I could use hot water (50C) instead of cold (10C). This got me thinking: what if I could use a delayed start so that I could have heated sparge water and also hit my strike temperature?
So after a bit of algebra, and some simplifying assumptions, you end up with the following formula:
vol_warm = vol_target * (temp_target – temp_cool) / (temp_warm – temp_cool)
Let’s try a simple example – we want 3.7G of 67C water for mash:
Warm: 3.7*(67-23)/(95-23) ~= 2.25, Cool: 3.7 – 2.25 = 1.45
And how about 3.5G of 76C water for sparge
Warm: 3.5*(76-23)/(95-23) ~= 2.55, Cool: 3.5 – 2.55 = 0.95
So now we can figure out that we need 2.25 + 2.55 = 4.8 Gallons of 95C water when we start out, and 2.4 Gallons of 23C water for “diluting”.
The night before, 4.8G of cold water to the GF and set the delayed start. At the same time collect 2.4G of cold water that will warm up to room temp … might as well treat both with meta-bite and hook up the chiller while we’re at it. Now at the start of brewing I just need to pump some of the hot water (sterilizing the chiller) into a new container/bucket and combine with the some of the room temp water, then add the remaining room temp water to the GF, and off we go! The right amount of sparge water and mash water at the desired temperatures.
I will definitly being trying this on my next batch
Follow-up (Oct-15): this actually worked, but I should have made more hot water; I didn’t anticipate the normal cooling off an un- insulated container … and it’s always nice to have some boiled water kicking around during brew day https://photos.app.goo.gl/pUYL2IKpyFEYjd7o2