BIAB- Trying to get it right this time.

After a couple less than successful biab batches, I am trying my third and want to try to get it better. I am trying BM's SWMBO Slayer Belgian recipe and am trying to figure out how much water to start with. I have a 50 qt brew kettle and like to sparge with 1 gallon, but I don't think I got my water volumes correct the last couple of batches and resulted in very low OG's. Any advice would be much appreciated.

It depends on your batch size and boil off rate. You said that you had very low OG, did you hit your desired volume? Also it might be easier until you get consistent results to cut out the sparge. I do all of my BIAB batches no sparge and have not had any efficiency problems.

To answer your question: For my system, I target an into-the-fermenter batch size of 5.25 gallons and I boil off 1.25 gallons/hour. If you take into account a typical grain absorption of 0.125 gallons / lb (you can minimize this further by squeezing the bag), my starting volume would be 7.625 gallons of water for a 9 lb grain bill.

I'm starting with 10.25 lbs of grain, but I don't know how to calculate boil off rate. I want to wind up with a 5 gallon batch. The recipe calls for a 60 min boil and a 60 min mash.

Done a few BIAB myself...easy peasy...you can go with 7 gallons all day long...you'll loose a bunch in the grain, you'll loose a bunch in boil off, and likely need to top off your fermenter for 5 gallons.

I've gone this route each time and it is fairly spot on.

Good luck!

The best way to figure out boil off rate is to measure it directly. Meaure out water and boil for an hour and measure how much you have left.

It's okay to underestimate boil off and end up with less volume than you expected. You just top off.

Low final gravity with correct volume means you need more grain. You can calculate what your original gravity is *going* to be be measuring pre-boil specific gravity points. Volume x Gravity Points is constant. So 7 gallons preboil at 1.035 is the same as 5 gallons post boil at 1.049 because 7 x 35 = 5 x 49.

If your you preboil gravity is too low then then your efficiency is low. Adjust with more grains *next* time. (and this time either boil down to a smaller batch or add DME)

Thanks everyone! Todays batch went flawless with your advice. Started with 7 gallons and came out to exactly 5 gallons in the fermentor with an OG of 1.051. Thanks again! :rockin::rockin::rockin: