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Est Pre Boil Volume and Boil time


Jan 28, 2018
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Switching to BIAB. Have a question about Est Pre boil volume and boil time in equipment setup. Does this number equal the total volume I start with or is this an estimate of the volume after mashing and bringing the water to a boil? Changing this changes my IBUs a lot. I'm thinking it's the total amount of water that I start with, before mashing.

Also, almost every where I read says a 60 min boil after mashing is sufficient, but the default in Beersmith is 90 min. Thoughts?

This would be the same as it is for regular all grain brewing. It is the volume you will be boiling. Once you either finish draining the bag or sparging, whichever you do, BIAB is no different than regular all grain brewing.

Most do 60 minute boils. You might want a 90 minute boil if you are using European Pilsner as a base malt.

That's why I asked what my est pre boil volume is defined as. I am currently partial mashing only.

By your answer, I'm assuming the est pre-boil vol is the liquid left after my mash? Taking into account loss from evaporation and the grain absorption?
Yes, it takes into consideration any losses before the boil. Didn't know what type of brewing you were switching from. BIAB is a good way to get into all grain brewing. I brewed all grain before ever hearing of BIAB and now in the warmer months do BIAB. I brew outdoors, so during the winter here it's out of the question.
OK, so my next question would be how do I determine how much water I should start with? I've entered my grain, hops and expected boil off rate into 4 different online calculation tools and gotten anywhere from 7 gallons to 8 gallons of starting volume. That seems like a big variance.
Each calculator makes assumptions about loss to grain absorption and process waste (mash tun loss, trub, etc.) so comparing different calculators without specifying the same process parameters for each is looking for confusion.  Since you (I assume) have the BeerSmith software, start with that.  You need to make a custom equipment file which represents your process with regard to mash tun volume and composition (specific gravity, weight), your boil off rate, process losses, etc.  Once you have that down, BeerSmith will use this profile, once you specify this new profile in a recipe, to give you an estimate of the amounts of water you need to start with or add during the process.

Brew it and take careful measurements and enter them in the 'sessions' tab of your recipe where there are 'measured' values.  If you are off in your estimations of boil off, water volumes, and gravity, you will see it pretty quickly.  BeerSmith will also recalculate your mash and brew house efficiency and you can use this information to update your equipment profile for next time.  The more accurate the measurements and the more time you spend getting the right information into the program, the quicker it will start giving you accurate estimates of what you will need for volumes.
The reason for the variations is likely the fact that each of the online tools is assuming a different equipment profile. Assuming you're using Beersmith, you set up your own equipment profile and mash profile, so the volumes will be as close as what you enter about you equipment allows. During the first few batches you will fine tune the profiles and then be pretty consistent. If you need help setting up an equipment profile, here's a link to a very helpful video: http://brulosophy.com/2014/08/04/beersmith-tutorial-equipment-profile-setup/