# What is First Rest Temperature

Discussion in 'Beginners Brewing Forum' started by Brewer #230611, Jan 10, 2020.

1. ### Brewer #230611 Member

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#1
Last edited: Jan 10, 2020
I have a robobrew and i'm trying to figure out how much water i need to boil for my mash, and the temperature etc. I've been looking at this tool: https://www.brewersfriend.com/mash/ but i'm not sure what all the terms mean.
What is first rest temperature?

This is the recipe that I am using: https://www.ontariobeerkegs.com/v/vspfiles/assets/images/grainkit - obk chocolate milk stout.pdf

My friend, who also has a robobrew told me that I should plug in 0.35 for the mash water/grain ratio based on his experience.
So i guess my question is, is the first rest temperature the temp of the water when i start adding the grains? The recipe says I need to mash at 150F/65C. Is that the value? Sorry for being such a noob.

Also, is this the right approach for calculating the right amount of strike water? I assume that my grains will absorb 1.5 gallon of water; 1 gallon will evaporate.

This is the calc I have:

+ 4.5 g (for mash, per the calculator)
- 1.5 g absorbed by grains (how do you calc this?)
-----------------------
=3 g left in mash tun by the time sparging starts.

If desired finished product is 5.25 gallons, i need to:

add 2.25 g of sparge water to bring it up to 5.25 g. And then tack on another 1g for evaporation during the boil.
So .. total water is 4.5 g mash + 3.25 g = 7.75 G
Does that sound right?

Thanks.

2. ### Brewer #230611 Member

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#2
I guess what i need to know is how to calculate how much sparge water I need ... based on the final amount of beer I want to end up with.

3. ### BarbarianBrewer Well-Known Member

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#3
I don't use an all-in-one system but the following should still apply if you do the standard mash-drain-sparge-drain method.

The standard formula for water absorption is 1/8 gal per pound of grain. So 12 lbs of grain will absorb 1.5 gallons of water. (12 * 0.125=1.5). For the sparge I take my desired pre-boil volume and subtract the mash runoff (called First Runnings). Pre-boil volume would include evaporation from boiling. From what you indicate your pre-boil volume would be 6.25 gallons (5.25 gal in fermenter + 1 gal boil-off). So, 6.25 - 3 gal (first runnings) = 3.25 gal sparge water.

4. ### BOB357 Well-Known Member

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#4
Probably a good idea to read the documentation for the Recipe Builder located here:
https://docs.brewersfriend.com/recipe-builder
As with any program, there is a learning curve and having a working knowledge of the different functions is a good place to start.
The recipe builder, along with your inputs will calculate the volumes for you.

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