Small batch BIAB - efficiency question

Discussion in 'Homebrewing' started by Graeme24, Nov 2, 2018.

  1. Graeme24

    Graeme24 Initiate (165) Dec 16, 2008 Ireland

    Hi all,

    Last weekend I brewed a small batch (5 litre) brew in a bag and it's the first time I've brewed at such a small scale. I am using a 12 liter stock pot which meant I had enough capacity to use my total water volume for the mash i.e. no sparge.

    My anticipated OG was 1.060 but I ended up 10 points short at 1.050. Part of this may have to do with the fact that in calculating my water volume I anticipated my normal grain absorption rate of 1 litre per kilo of grain. Given that I was using my total water volume for the mash I should have known that the rate of absorption would actually be much lower. It ended up being around 0.5 litres in total which meant my pre-boil volume was about one litre more than anticipated. And this was without squeezing. It would likely be a little more if I did squeeze.

    Anyways, although it's hard to determine that this was the only factor in my low efficiency I wanted to know are there any benefits in sparging if capacity is not an issue?

    cheers for your input!
  2. VikeMan

    VikeMan Meyvn (1,476) Jul 12, 2009 Pennsylvania

    The grain/wort absorption should not change (in terms of wort volume units per grain weight units) just because you mashed with all your water. You got more wort out of the first (and in this case only) "runnings," but that's because you put more water into the mash, not because the grains absorbed less. Now, if you somehow had managed to decrease absorption, that would ultimately increase mash efficiency, not decrease it.

    So let's look at your mash efficiency. You were expecting an OG of 1.060 in 5 liters. You got 1.050 in 6 liters.

    60 points x 5 liters = 50 points x 6 liters

    You got exactly the mash efficiency expected. Mash efficiency is the percentage of total possible sugars/dextrins that actually make it from the mash tun into the brew kettle, regardless of how much water those sugars/dextrins are dissolved in.

    My guess is that your grain absorption has always been a little lower than whatever number you were using, and that this became more obvious when you did this small batch. The way forward would be decrease your grain absorption parameter to match what you saw (assuming you normally do BIAB). This should drive your software/spreadsheet/back of the envelope to tell you to use less total water.
    frozyn and PapaGoose03 like this.
  3. Graeme24

    Graeme24 Initiate (165) Dec 16, 2008 Ireland

    That all makes perfect sense to me. I was probably overthinking it! Thanks for the level of detail :-)
    riptorn likes this.
  4. dmtaylor

    dmtaylor Aspirant (208) Dec 30, 2003 Wisconsin

    I'm a small batch BIAB brewer. I usually sparge, and can get efficiency up to 90%+. There are definitely benefits to sparging even with BIAB. And it's so damn easy -- heat up some water, move the bag from one container to the next, then collect all the wort and boil it up as normal.
  5. Graeme24

    Graeme24 Initiate (165) Dec 16, 2008 Ireland

    Hi there and thanks for your input! Sparging would be of no extra effort to me. The only reason why I did not sparge separately is because my stock pot can easily accommodate the total grain and water volumes. I am curious as to whether mashing and sparging separately Vs mashing with the entire water volume would yield a more efficient wort. If it would then I'd be happily go this route going forward
  6. VikeMan

    VikeMan Meyvn (1,476) Jul 12, 2009 Pennsylvania

    It would. It's because the constant wort volume left behind will be of lower gravity, thus higher avg gravity wort makes it out of the grains.
    Graeme24 likes this.
  7. Graeme24

    Graeme24 Initiate (165) Dec 16, 2008 Ireland

    Thanks for clarifying that. I'm going to give this a shot tomorrow
  8. Graeme24

    Graeme24 Initiate (165) Dec 16, 2008 Ireland

    How long to your sparge for? 20 minutes?
  9. frozyn

    frozyn Zealot (577) May 16, 2015 New York
    Premium Trader

    Second this. I usually do not sparge on most batches as I hit 72-74% efficiency, but big beers (9% or more) get a sparge of "here I'll turn on the faucet for a short bit and run it over the bag Oh! that seems like enough." That tends to get me to 70-75%. I call it channeling my inner @GormBrewhouse.
    dmtaylor likes this.
  10. dmtaylor

    dmtaylor Aspirant (208) Dec 30, 2003 Wisconsin

    No need to wait. Stir it up then pull the bag. About 2-3 minutes.
    Graeme24 likes this.
  11. gvickery

    gvickery Aspirant (276) May 13, 2017 Texas

    I do regular size (5-6gal) BIAB and I started off with a tall narrow turkey fryer pot. I switched to a short wide pot (12"t X 16"w) and noticed a big difference in the mash. I guess maybe the grain is more loose. Perhaps the grain is all compacted together and you're not getting enough of it exposed to the mash water? Just my guess.