Wednesday, March 18, 2009

How to do a multi rest infusion mash

This is for fellow Home Brewer Blake who was curious how I do protein rests or multiple rest mashes with a cooler mash tun. Since I do mash in a LARGE cooler I can not raise the mash by direct heat. This involves a few extra calculations if your doing more than a single infusion.

To get started we need to know several variables, grain mass, grain to water ratio(lb to qt) and ambient temp of grain. I am going to use my Czech Pils mash program as an example.

Ambient temp of my grain is 65F, which will change throughout the year. This is important to know since you will be raising your first rest from this temp. I am using 1 qt of water for every lb of grain. There is a almost 14 lbs of grain. Since I am using continental pilsner malt we want to do a protein rest at 130F for 30 minutes and Sac rest at 154 for 60 minutes. I did not mash out but we will go ahead and pretend I did for the sake of this example.

First Rest:

Infusions Temp = (0.2/1)(130 - 65) + 130
So we divide the ration by .2 to get .2. Target Temp - Ambient Temp is 65.

Infusion Temp = (.2)(65) + 130 or 13 + 130

So out first infusion is 14qt at 143F. This should allow for us to meet our target temp of 130F.

Second Rest:

Crank your burner up during the first rest and get your water to a boil. We are going to ad smaller amounts of near boiling water to move our temperature to the saccharification rest temp of 154F.

amount of boiling water = (154 - 130) x (2.8 + 14) / (210 - 154)

(Sac Rest temp - protein rest temp) X (grain mass + water) / (infusion temp - sac rest temp)


amount of boiling water = (24)(16.8) / 56


amount of boiling water = 403 / 56 or the amount of boiling water is 7 qt to reach 154F.

Third rest:

No we are going to end conversion by mashing out or bringing the mash up to 170F.

So far we have added 14qt + 7 qt for a total of 21 qt of water. This is the main reason I do not mash out unless I have enough room in my tun. Sometimes on larger beers this is not a possibility but I just lauter with 170F water to compensate.

amount of boiling water = (170 - 154) X (2.8 + 21qt) / (210 - 170)


amount of boiling water = (16) X (23.8) / (40)


amount of boiling water = 380 / 40 or 9.5qt of near boiling water to reach 170F.

So far we have added 32.8qt of water to the tun or 8 gal. This is why I often forgo a mash out and just start the lautering process.

If you want a great introduction please go to HOW TO BREW , this is where I learned this equation. John Palmer gives a very understandable introduction to the mashing process.


Blake Jarolim said...

Does the .2 at the very beginning of the equation(s) come from it needing to be 20% percent more or does that number fluctuate depending on what you are brewing?

Slovak Brewer said...

Its a thermodynamic constant. I don't understand the concept but I believe it figures for heat loss. It would be .41 if you use metric measures.

Blake Jarolim said...

Yea, that's a bit above my mental prowess as well. Just as long as I know that it stays the same each time.

When you are adding the 210 water, do you add it a quart at a time or all at once?

Blake Jarolim said...

I also wondered how you figured 2.8 for the grain mass. Is that in terms of cubic feet?

Slovak Brewer said...

2.8 is thermal constant X grain mass.
or .2 X 14 in that example. I have a 1 quart pyrex that I pour over a slotted spoon. I add .5 gallon increments and stir to avoid hot spots.

jhicks999 said...

I am a programmer who enjoys brewing beer so I created a small program to accomplish this. I just need to know the variables to fill to do this.