Partial Mash: Mash Tun Too Full

Hi All,

I did a partial mash Robust Porter the other day. I use Beersmith to calculate volumes, temps, etc. for my 2 gallon cooler partial mash system.

Here's my problem: my mash tun was full before I got all the mash water in.

Beersmith calcs:
4.85 lbs of grain
1.25qt/lb = 6.06 qt
Tun volume required = 1.89 gal

However, I could only get 5 qts of water in my 2 gallon cooler (with the 4.85 lbs of grain. this should fill 1.63 gal). As a result, my temps were all off and I had no room to add boiling water to correct the temps.

Why would 1.63 gallons fill a 2 gallon cooler?

I use a grain bag, so there's really no dead space in the mash tun. Also, I reserve the right to have done something really stupid, like mis-counting the amount of water added, but I don't think that's the case.

Any thoughts?


(This is my first thread, but I've lurked here for a while. I've learned a TON of stuff from this forum, so thanks to everyone.)

First thought: time to build a MLT out of a BIG cooler and move to all grain so you don't have this problem again.

Second thought: seems to me the crush of the grain probably determines the actual volume required. Maybe Beersmith's calcs are based on something different. Shooting in the dark here, so refer to my first thought.

The most I've been able to mash in my 2 gallon cooler is about 4 lbs of grain. I use 1.3 quarts/lb and it fills it to the very tip top of the cooler.