Biab Can I Do Full Batch In My Urn?

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Staff member
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I am seeking some advice from the BIAB gurus.

I have a 25l Birko Urn that is obviously not big enough to hold the full volume of water and grain for a 23 litre batch.

I have plugged my recipe into the BIAB Designer Spreadsheet. My total grain bill is 5.7lg and it suggest I need to mash in 31litres

Could I do the following?

Method 1
Mash in 20 litres in the urn
Prepare 11 litres on stove top as strike water
At the end of the Mash - lift bag into a bucket and rinse grain with prepared water
Pour half (roughly) of the sparge water into the urn and commence boil
Gradually top up the urn with the remaining water as it evaporates


Method 2
Mash in 16 litres - Sparge in 5litres to bring bring boil volume to 21 litres
At the end of the boil top up (either in urn or fermenter) to the desired 23 litres with boiled water

My thinking is that if the grain bill is based on a 23 litre batch but mash and boil are less I am making a more concentrated wort just like my kit and extract days that I can top up with required amount of boiled water.

Thanks in advance for any advice


"Grains don't grow up to be chips, son"
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Definitely cant do the first option.

Your urn is 25lt. If your grain is nearly 6kg's it'll displace nearly 6lt's. So if you want to mash with 21lt, you'll overflow big time.

Second option is therefore most likely, however i've never topped up during or after a boil (high gravity brewing).

EDIT: Have you calibrated and measured the volume your urn will hold? I think by law, a vessel must hold at least what they say it will, but a lot of pots, urns, etc will actually hold more.
Case in point - the other week i bought a stainless pot advertised as 50lt, but it actually holds almost 57.
Today i bought a small urn from Radio Rentals (kambrook brand) to use as a sparge water vessel. Advertised as 8lt's but she'll hold 10 easy. I know in an urn or any vessel that is designed to heat water, they probably err on the side of caution in case you decide to boil 10lt's in an 8lt urn so you don't hurt someone, but if your urn holds more, you may be able to mash in it and then just a small top up or sparge through the grains to get to a boil volume. You'll need a preboil volume around 25-26lt's to go this way....


Well-Known Member
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My view is that if you're adding any water up until the end of the boil, ensure that it does something constructive for you. So, use all of that mash overflow for sparge.
With a limited kettle volume, by the fermenter dilution route you can also break free of the shackles some folks have with a fixation on numbers and targets. That makes life very, very simple, albeit at the expense of variable brewlength, however once you've done a few you'll get a feel for it and unless your efficiency is all over the place you'll get 23 in the fermenter every time, often with a little surplus (used in starters). Electric MaxiBIAB is what it would be, I've not tried it but there's really no reason why not. For Pete's sake, we know it works at 19L Stovetop, I am eying off a 20L urn for it (long term project of mine <_< ), you should be fine with a 25L jobbie! B)


aus Bier hergestellt
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My brewing is currently all done in a 19L pot on the stove. The best advise I can give is to top up with sparge water during the boil to replace evaporation. This ensures you get as many of the sugars into the brew as possible, and do a 90min boin instead of 60. The longer boil means more evaporation and so more volume you can replace with sparge water. At flameout, I then topup right to the brim of the pot. This ensures any trub losses in the pot are as diluted as possible (reducing the loss of presious sugars). Then just top up with water in the fermenter to either the desiered volume, or to the desierd gravity (your choice).

High gravity brewing does mess with hop calcs, but the important thing here is consistancy. After a couple of brews you'll get a feeling for how to compensate (and really - do you know what 25IBUs tastes like vs say 22 or 27).

And in a 25L urn, you'll have an eaiser time than those of us with a 19L pot, since you have an extra 6L of volume.

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