Credit To: http://www.rackers.org/calcs.shtml
Calculate the amount of boiling water you need to raise
your mash to the next rest temperature.
Note from an Expert:
Credit To: http://byo.com/mrwizard/1327.html:
...if you use room temperature malt and determine the water temperature needs to be 162 ºF (72 ºC) to hit a mash temperature of 150 ºF (66 ºC) and you come in at 148 ºF (64 ºC), use hotter water the next time around. As long as your malt and mash tun are at room temperature (or your mash tun is always pre-heated to some temperature) and you know the ratio between water and malt you can empirically determine an off-set. My rule of thumb for infusion is to add 12 ºF (7 ºC) to the desired mash temperature to determine water temperature. This assumes a 3:1 ratio between malt and water and that the malt is at 68 ºF (20 ºC).