Water quantity help

[creepyjackalope]

Hey there folks. It's brew day and I'm doing a couple of new things. Doing a protein rest (wheat in the bill), which I've never done, and a 90 minute boil (Pilsner in the bill), which I've never done. Using an online calculator, I get the following quantities/temps.
12.5 lbs grain - 15.63 quarts at 130 degrees to hit 122, then 7.4 quarts at boiling to hit my mash temp of 148.
What I don't know after this is how much sparge water I'll need (batch sparge). Any help would be very much appreciated.
This is for a 5 gallon batch.

 

[CadillacAndy]

There are a couple numbers we're missing here. What's your boil off rate? What is the dead space of the mash tun?

If you don't know these numbers, they're easy to figure out.

Put a couple of gallons of water in the mash tun and open the valve. Let it drain until it's done, dump the remaining water into a measuring cup, and see what it reads. That's the dead space.

To get your boil off you can just wing it and guess about a gallon per hour, or you can get a couple gallons and boil for 15 mins, calculate the loss and multiply it by 4 and you have your boil off.

You'll also need to find the amount of water each pound of grain absorbs. That's a pretty set variable, I just don't have it in front of me.

 

[Denny]

Don't do a protein rest at 122. You run the risk of a bodiless, headless beer. In fact, I say don't do a protein rest at all, but if you must, do it at about 131F.

 

[CadillacAndy]

Don't do a protein rest at 122. You run the risk of a bodiless, headless beer. In fact, I say don't do a protein rest at all, but if you must, do it at about 131F.

I totally agree with this. I glossed right over that part when I read it.

 

[Denny]

You'll also need to find the amount of water each pound of grain absorbs. That's a pretty set variable, I just don't have it in front of me.

In general, .12 gal./lb.