# BIAB Grain Absorption and Evaporation Loss



## brassjc (19/11/17)

Hi all,

I have now brewed 6 all grain brews using BIAB method with a 32L pot (diameter 37cm) and am consistently getting a grain absorption loss of 4L from average 5.5kg grain bills, despite how much squeezing I try, which from reading seems high?

Secondly, I am getting 8L evaporation loss for 60min boils which also seems pretty high? Perhaps my boil is too rapid?

Any thoughts or tips appreciated!


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## TwoCrows (19/11/17)

4 - 6 litre loss is normal for that size grain bill.
You should be losing about 4 litres in an hour boil with that volume.

I start the boil with 32 ltrs, losing 4.5 ltrs in an hour boil. Lose some getting up to temp, 3 litres lost to trub and dead space.
I get 23.5 litres into fermenter.


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## MitchD (19/11/17)

What you want is consistency, which it sounds like you have. 

Grain absorption seems fine as beersmith (assuming you are using this software) estimates biab absorption to be around 0.5l/kg, you can adjust this value in BS if you can accurately work out where yours sits.

Boil off seems high but it is all dependent on pot diameter and energy input, again you can set this in BS but if you are consistent I'd leave it.


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## manticle (19/11/17)

Sounds fine. I work on 1- 1.1L per kg of grain absorption plus trub (although I run off to kettle - in biab you won't so trub loss is all in one at the end.

Is that 8 L entirely evap or is some loss to trub/deadspace?

Doesn't seem ridiculous, better to boil well than inadequately for the sake of a couple of pints.


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## brassjc (19/11/17)

Cheers guys, can confirm that the 8L is only evaporation, I leave another 1L due to trub loss. I would much rather a vigorous boil than something just breaking the surface so with my calculation based on my brew pot capacity it seems I need a larger pot have enough first runnings to reach my targeted batch volume considering trub and fermenter loss, which is what I have been thinking


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## brassjc (19/11/17)

And yes using BeerSmith 2 app, although I’ll admit I’m still getting used to it. I’ve added my brew pot as a new piece of equipment as there wasn’t anything comparative, and that was skewing he results significantly


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## TwoCrows (19/11/17)

You could get a Big W 19 litre pot for $20 and balance out the total volume of wort required between the two, boil using both pots and then add them together into the fermenter.


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## brassjc (19/11/17)

Could do @TwoCrows but would prefer one vessel at the moment


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## brassjc (19/11/17)

So my calculations for my last brew was:
25L strike (that’s the max with grain I can do in this pot)
Mash
-4L grain absorption loss
=21L
+6L “sparge” (pouring over the bag and then squeezing)
= 27L
Boil
- 8L evaporation
= 19L post boil
- 1L trub
= 18L into fermenter
- 2L fermenter loss
= 16L batch

I really want to be shooting for a 19L+ batch to transfer to corni keg though...


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## Andy_27 (20/11/17)

I've done a 10l batch sparge with that much grain before. I started with the same strike water too. It came out well, heaps over my estimated OG though. Maybe try that?


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## Sidney Harbour-Bridge (21/11/17)

Could you top up during the boil with boiling water?


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## Liam_snorkel (21/11/17)

^ this. Easiest would be to top up in the kettle.
Or, get a 20L plastic bucket and do another 'sparge' with a few extra litres, and top up the kettle mid-boil as room allows.
also depending on the style of beer you could look at shortening the boil (flamesuit on), hoppy pale ales that are to be drunk quickly can be done with 30~20min boils.


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## Liam_snorkel (21/11/17)

oh and unless I missed it, are you using gas or electric?
If electric, you could wire up a voltage regulator to control the boil vigour.


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## brassjc (21/11/17)

Gas, using my bbq wok burner. That’s why I thought I could probably turn it down a bit as it’s a pretty strong boil


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## Liam_snorkel (22/11/17)

yep, not a bad option. You only need it to be _just_ boiling, and if you're tight for volume that would be preferable.


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## ballantynedewolf (8/12/17)

brassjc said:


> So my calculations for my last brew was:
> 25L strike (that’s the max with grain I can do in this pot)
> Mash
> -4L grain absorption loss
> ...


I have faced this exact situation with my 35L kettle. I think you are doing well with your 1L trub loss, could do better with fermenter loss. Remember fermenter loss can be mitigated with a nice big yeast starter - of which more later.

You have a few choices. Simplest is to go Belgian and add sugary water at the end of the boil. Sugar is cheap (to you) and keeping a low percentage will not affect your beer body noticeably. If making a dark beer you can use treacle, which has unfermentables in it, thereby maintaining body. If making a large starter, you can add sugary water via the starter.

The option I've gone for is Maxi-BIAB - http://www.biabrewer.info/viewtopic.php?t=352
This will change your life! The principle is that you brew a big beer and dilute post boil. I find I can do pretty good calculations with the BIAB.info spreadsheet called The Calculator, even though it's not perfectly suited to this style. A concern often expressed is losing efficiency because of the lower liquor to grist ratio, but with a nice fine grind, I'm getting 90% mash eff with a L:G below 4:1.

Perhaps the trickiest part is getting your bitterness addition right. You have to calculate the IBUs for the full, final, diluted volume, and then bump the hops up some more to account for the lower utilisation achieved in a higher gravity wort boil (don't use a bag or spider - that further lowers utilisation. My next brew looks like needing 120g of Fuggles for 25.4IBU in 44L of 1.043OG wort - that's $12 worth of hops for bittering alone - so I'm planning to try this https://www.homebrewtalk.com/bittering-hops-in-15-minutes.html where you make a hop tea in the pressure cooker. It takes 10 mins and no cost for the high gravity wort.

I think you're losing too much to boiling. An hour at 4L loss per hour should be plenty.


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