So I took a stab at a brew in a bag today an have a question. I had just shy of 11lbs of grain. I referenced some of the BIAB directions from NB to get a rough idea on some things, but used my own recipe (American Pale Ale). On the NB kit info sheets it says to start with 5.5 gal of water for the BIAB process. Seems like a lot, but I went with it seeing as I use a 10 gal. Megapot with plenty of diameter for evaporation. As expected, my OG was fairly low - 1.043 (1.032 pre boil). I mashed at 153-154 for 60 min. 60 min boil. Went to the fermenter with 3.75 gal or so.
I’m assuming it’s the starting water volume that is causing the OG to start low. Thoughts? Not really concerned (as this is my first attempt), but would like to hear people’s feedback. Worst case it’s more of a session beer.
Use mashwater 3.3
Even though you are not “sparging”, the volumes should still be the same for grain absorption and boil off.
I did the 3 gallon oatmeal brown ale and ended up with the same post boil volume. I may try to reduce the starting volume next time.
The sreadsheet I made shows a little above 4.9 gallons starting water…this is to end up with 3.25 gallons into the fermenter. Assuming 11 lbs of grain with 10 oz absorbed per lb of grain. Your evap rate some other things might tweak it a bit here and there. But, it’s close.
Did you squeeze the bag?
Shows 4.78 starting gallons for that recipe.
I do 3-gallon BIAB in a 5-gallon pot on my electric stove. I use 4 gallons of strike water, get about 3.5 gallons in my kettle, 3 gallons into my fermenter and bottle a case. I might see a quart difference one way or another depending on boiloff (which varies a lot for me) and amount of grain, but this gets me pretty close. I am a squeezer, by the way.
If you were over your expected volume by 3/4 of a gallon I’d say that probably accounts for the low gravity. That said, with BIAB you can really crush those grains because you don’t need to worry about a stuck sparge. I mean, you don’t want to be sticking a bag of flour in the water, but you can definitely get away with a finer crush than a normal all grain brew which can help increase efficiency.
Do you have your own mill? If not I would at least run the grain through the store mill twice. Should help a bit. That and correcting your volumes.
I’m pretty new at these forums, but if I could chime in…
There’s a pretty good article this month in Zymurgy magazine about BIAB brewing.
They say that a good rule of thumb is to allow .075 gallons water absorbtion per pound of grain. Back of the envelope math says that’s about .825 gallons lost to grain. Then you need to add in what you epect to evaporate off. I presume you know your system, but they also say about a gallon an hour is a rough guestimate (with a big pot and relatively small wort you may lose more than that.
Therefore, for a 3 gallon ending, you’re looking at roughly 5 gallons (maybe a tad under) to use for your mash.