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how do you calculate the correct amount and temperature of water and to offset the amount and temperature of the grains?

Perhaps there is a formula or rule of thumb that I am missing.

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up vote 4 down vote accepted

I've found that software and calculations can get you close, but not exact. There's too much variability in each brewer's system. You kind of have to get a feel for your brew system over time.

First, take out as many variables as you can. Always start with your grain at the same temp. Always start with your mash tun at the same temp before pre-heating it. If you're pre-heating your tun, always do so with the same amount of water at the same temp for the same amount of time before doughing-in.

Next, keep good notes so you can look back over previous batches to see how much total grain you used, how much strike water, what temp the strike water was, and what mash temp you hit. Over time, you'll get a good feel for how far over your target mash temp your strike water needs to be.

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+1 google mash strike water calculator to get in the ballpark and then adjust for your system. – Tom McCann Feb 22 '11 at 18:26

Palmer, in How to Brew, has some formulae (though that doesn't really work for the beer i just brewed... it's about 10 degrees short). In a previous page, he mentions getting your strike water to 10-15F warmer than your target mash temperature.

I use ProMash, and just punch in the strike temperature i'm aiming for, the temperature of the grain, and the amount of water and grain i'm using, and its strike temperature calculator does the work for me.

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Another Promash user here. I find it remarkably accurate and easy to use. – Denny Conn Feb 22 '11 at 16:31

I keep this site handy: http://www.rackers.org/calcs.shtml

It gives you: a Strike Temperature Calculator (how much water & what temp to start mash with), a Rest Calculator (water volume to mash out), and a 'Can I Mash It?' calculator (is my mash tun big enough to mash X grains at Y water/grain ratio).

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