My Brew In A Bag madness or methodology-you choose. BIAB calculations

Update – See here for first timers looking for a way to figure out mash water volume (click)

I’ve been doing all grain using the Brew In A Bag (BIAB) method for about 18 months now and thought it may be good to put my methods down in writing for posterity and perhaps help others.  Yesterday I did an OktoberFAST batch and took careful notes, so here goes.


  • 4# Pilsner
  • 2.5# Vienna
  • 2# Munich
  • 1# Aromatic
  • 1# Crystal 20L
  • 0.5# Carapils
  • 0.5# Crystal 40L
  • 1.4 oz Tettnanger Hops for 60 Mins
  • 0.7 oz Tettnanger Hops for 45 Mins
  • 0.7 oz Tettnanger Hops for 30 Mins
  • Safale S04 dry yeast
  • 90 minute mash
  • 90 minute boil
  • 5.25 gallons
  • OG 1.057 @ 75% efficiency
  • 23.4 IBU
  • 10.5 SRM

I got my stuff from Brewmaster’s Warehouse and saved the recipe here: OktoberFAST in case you want to try it.


I first want to get a total water volume required.  I know from my past calculations that my grain will absorb about 0.5 gallons per pound of malt so that’s 11.5 X .05 = 0.575 gallons.

My batch size is 5.25 gallons.

My boiloff rate is 2 gallon per hour so 2 X 1.5 = 3 gallons.

Total water needed = 0.575 + 5.25 + 3 = 8.825.  I’ll measure 8.8 inches in my pot since 1″=1 gallon for my pot.  All of the water in the mash would give me 3 qts/# thickness, I can thicken this up a bit by doing a mash out sparge.  I have found it makes things easier and gives me better efficiency when I do this so I normally do.  I will save 2 gallons for a mash out so I put 6.8 inches of water in my pot and begin heating.

I use the 6.8 gallons of water in my water adjustment spreadsheet to find that I need the following salts:

  • 1-3/4 tsp Chalk
  • 4-1/2 tsp Epsom
  • 4-3/8 tsp Baking Soda
  • 6 tsp Salt

Yeah, my water is pretty void of minerals.  I find it hard to adjust to a certain profile so I usually just adjust to meed the SRM then check the chloride to sulfate ratio to fit the malty/bitter profile for the beer I am brewing.

I take the temperature of my grain and find out I need 162.5F for the 6.8 gallons of water plus grains to hit 156F mash temperature.  I’m not critical on this step for this beer because it is just important to be above 152F.

Once I hit mash temperature, I dissolve the salts in a smaller bucket of the mash water and set it aside.  I put wok grate in the bottom of the pot and hook my bag into the pot.  I made the bag myself out of a voille fabric.  Bag size is important, the pot should fit INSIDE the bag.  I use office binder clips to hold the bag onto the pot.  I can still put the cover on it then.  I slowly pour the grains in and stir out all the dough balls.  I pour the dissolved salt water in and stir again.  I cover the pot then wrap it in an old comforter and set the timer for 90 minutes.  I find 90 minute mashes give me good results.  The first half hour or so I may stir the mash once or twice.

With about 15 minutes left in the mash, I move the kettle off the burner and onto a side table.  I use the pot that came from my turkey fryer with the 2 gallons of water that I set aside for a sparge and heat it up to 170F+.  I set the pot on the ground next to the burner and reset the mash kettle onto the burner again.  Once the mash time is up, I unwrap the kettle, remove the cover, and unclamp the bag.  I gather up the ends of the bag and begin to lift it out of the mash water.  No pulleys needed.  I’ve handled a 23# mash before, it isn’t really too heavy.  I begin to twist the bag to tighten around the grains and continue to hold it over the water.  If I have a helper, I will have the burner on medium as I am draining.  I keep twisting and holding until the stream is fairly low then quickly move the bag over to the sparge kettle.  I dunk the bag in the sparge water a few times to make sure the hot water gets into the grain bed to knock the extra sugars out.  I then do the twist and hold procedure again.  I will then put the bag into one of my fermenter buckets and dump the sparge water into the boil kettle and fire the burner up to high.   I put a metal colander upside down into the turkey fry pot and put the grain bag ontop of that.  I use a metal pan cover to squish the bag against the colander and twist and squeeze and reposition the bag and repeat until I can’t get any more liquid out.  That wort goes into the kettle too and the grain bag goes into a 5 gallon round cooler with the end open for my sour mash two days later.

From this point on, the brew is like all other brews.  I boil and add the hops at the required time.  I chill.  I transfer into my carboy, pitch the yeast, and ferment.


The beauty of BIAB is it can be so simple, by not sparging, just use all your boil water in the mash.  But it can also be used for advanced techniques like decotion.  See, you have a fired mash tun so you can decoct or step mash with the full volume of water by just lighting the burner.  You can partigyle.  You can minimash a large batch of partial boil beer.

BIAB is NOT a stepping stone to the cooler mash tuns.  It is a legitimate alternative.  The quality of beer is equal to the traditional sparge methods.  There is some time savings.  There is significant equipment cost savings.  There is significant equipment space savings.  The calculations are pretty simple.  The concept is easy to grasp.  You can get a high quality wort with high efficiency.  You can do large batches (I’ve done 11 gallon batches).  You can do high gravity (you have a 15 gallon mash tun as opposed to a 5-12 gallon cooler).  No stuck sparges.  No grainbed channeling problems.  No astringency issues.  I heard there was a recent study that found the cloudy wort you get from BIAB is actually helpful to the yeast!


14 responses to this post.

  1. Posted by RdeV on September 21, 2010 at 9:50 am

    Hear hear! In many places now, BIAB is indeed a mature technique (prize- winning), just like the others but with some really clever advantages like you’ve spelled out above as is really quite simple to firstly calculate and then to execute.
    Many potential AGers are put off by an initial equipment outlay, then the risk that it may not be what the brewer is after, for what ever reason and they’re then stuck with this now- useless equipment. However, stovetop BIAB can be started with ease for <A$50, thoroughly recommend it anyone looking to try AG but are unsure if it will give them what they're seeking. After that, its just profit! But if they decide BIAB or AG just isn't for them, then its no great loss.
    There's probably a few vested interests looking down their nose and spreading mis- information about BIAB (even BN did this sort of thing lately (#670), some big names who really should've known better), honestly, be prepared question what you hear and challenge this crap, eg. only good as a 'stepping stone', can't do lagers, cloudy wort, haze problems, poor efficiency, etc- it is all just utter garbage!
    Just on the cloudy wort issue, it is just crap what is said about that being an issue with BIAB, there is no appreciable difference in what goes into the fermenter, which is where it actually counts, more- so the actual beer which is indistinguishable.

    Keep up the great work! 🙂


  2. […] seen some increasing traffic drawn to my BIAB methodology post and I imagine most are those with a new interest in BIAB. My water calculations comes from my […]


  3. Posted by Dave on December 6, 2011 at 2:02 pm

    Just did my first AG with BIAB. The recipe used 8.5 gallons preboil, 10# base malt, and 2# speciality malts. I mashed for 90 minutes at 60 minutes, rung out the bag over the kettle (no sparging of the grains though), and then a 60 minute boil. My OG was only 1042. Why so low? Thanks!


  4. Well, I’ll take the best stab at it I can. With 6 gallons post boil and the grains, you’re at around 60% efficiency which is close to no sparge.
    How much did you squeeze?
    Do you know how much water was absorbed?
    Check the mill of the grains, BIAB can be pretty well milled, I usually ask the online stores I buy from to double mill the grains.
    How is your pH?
    Stirring in the beginning of the mash helps.
    A mashout can help too, bring the mash up to 168ish and hold for 10-15 minutes.
    And lastly, it could just be one of those times that a number of things lined up against you. Your next mash could be perfect.

    I suggest copious not taking and take readings of everything you can as much as you can for your first few BIAB batches. Volume, gravity, temperature, etc. These notes can really help you dial in your process. I once took gravity and volume readings when I pulled the bag, when I added the gravity drippings from sitting in the colander, and then a few times as I squeezed the bag. Just to get some quantitative data for what I was doing. That’s how I found out my grain absorption and how much worth it was to squeeze the heck out of the bag. I usually get 80-85% efficiency and 0.05 gallons/# of grain with slight variance with high or low volumes of grain.

    Try a few of these hints you next beer and if it improves keep doing whatever it was that worked. In the meantime, you can make adjustments post mash but pre boil to get closer to your desired beer.
    Check your SG and volume post mash, you can boil longer to lower the post boil volume which will raise the SG of your wort pre ferment. Fiddle with your software to figure out IBU adjustments if you want.

    Good luck, and report back!


    • Posted by Dave on December 8, 2011 at 7:06 pm

      Thanks so much! I didn’t check my PH and only squeezed about a quart out of my grain bag. I ‘ll give it another try and get more measures along the way. Thanks again! Dave


      • A big squeeze will probably help you then. I literally put all my body weight onto it. We’ll just say you were practicing partigyle. But seriously, if you had taken that bag and put it in a new mash water you could have partigyled. Just something to keep in mind.

      • Posted by Dave on December 12, 2011 at 1:39 pm

        Thanks again. Did my second BIAB yesterday. Came in at 1042. A little low but probably about right for an American Pale Ale. I bumped it up with some DME so the post boil came in at 1060. Yes I cheated. 🙂 Great methodology!

      • Posted by Dave on December 14, 2011 at 7:51 am

        I forgot to mention. I usually put my bag and grains in when the before the water is heated. Should I wait until the water is at 66c before adding grains? Thanks!

  5. Raise the water to above strike temperature then put your grains in. If you don’t have software, tinker with these online tools:

    I cannot personally say exactly what the difference is between starting cold or hitting your strike temperature but you have to figure that bringing the grains through the different enzyme ranges will affect your finished product…for some beers that may be good, others not so much.


  6. Posted by Paul on March 3, 2013 at 9:19 am

    Great post. I’ll be subscribing to this blog thank you!
    I BIAB also and have found that I if I dunk my grains before I hit target temps I get a better mouthfeel and body in my beers. My efficiency may go up up a little but not much.


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