During my last batch of brewing I came across a formula for calculating the water temperature for a mash given the grain temperature and desired mash temperature. Unfortunately I can no longer remember where it came from. However, it is:
Ts = Td + 0.4 ( Td - Tg ) / R
- Ts is the water strike temperature
- Td is the desired mash temperature
- Tg is the grain/mash ingredients temperature
- R is the ratio of water to mash ingredients as litres per kilogram
I usually work with values of R from 2.5 to 2.75 depending on the volume of mash ingredients and how loose a mash I want. As my current mash tun is a plastic bucket with a false bottom wrapped in an offcut of an old duvet, I try to keep my desired mash temperature as close to 68C as possible. Over the course of a ninety minute mash I tend to lose about 2 to 3C.
This formula certainly seems to work fairly well for me. If anyone knows where it comes from or has a more reliable version I’d be pleased to hear about it.