Full Volume BIAB

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Meatymc
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Full Volume BIAB

Post by Meatymc » Thu Mar 28, 2019 8:40 pm

Whilst this is a question about my BIAB brewing it's really about grain utilisiation so thought it best to post here.

My brewing is limited by equipment and facilities which means I BIAB in a 30L pan, dunk sparge to get pre-boil volume, use bottled gas for heating/boiling and no chill - carting everything from the house to the garage to brew.

I may be able to afford a new pan - 50L (happy with 5 gallon brews) - which would cut out the 'sparge' and allow me to go from mash to boil without the pain of carting yet more hot water out and transferring the grain from one vessel to another to get to boil volume.

Obviously, what I do now means I have a higher gravity in the mash and a lower gravity in the sparge - ideally reaching my target pre-boil gravity when adding the 2 together. Now here is my query.......

When I looked up full-volume BIAB everything I've read says you have you use more grain to get your target gravity but don't get why if the pan is large enough for all the grain to be suitably exposed to the liqour.

What am I missing?

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Jim
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Re: Full Volume BIAB

Post by Jim » Fri Mar 29, 2019 9:47 am

Disclaimer: I've never done biab. (But that isn't going to stop me having a go at this question. :) )

Not sure what you mean by dunk sparge but if you mean dunking the bag of grain in water in a different vessel, then adding the resulting weaker wort, that might get you better utilisation (i.e. remove more sugar from the grains) than doing a single large-vessel biab where there is effectively no sparge. The reason being that the mash will already have a lot of sugars in it, so will be less able to take more out.

That makes sense in my mind, anyway.
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Meatymc
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Re: Full Volume BIAB

Post by Meatymc » Fri Mar 29, 2019 10:26 am

Morning Jim

Yes, you've got it in one (the dunk sparge explanation). It's the only way at the moment I can wash any residual sugars out of the grain after the mash and get the desired volume for the boil. I did check the mash and sparge water once to see how they compared and although I can't seem to lay my hand on the result, I seem to recall the mash was about 1050 and the sparge around 1020 after stirring for about 10 minutes. Add the 2 together and I was close to my target pre-boil OG.

That's why I don't get what seems to be perceived wisdom in that to acheieve the same end result when doing a full volume mash you have to use more than the equivalent grain bill - just doesn't seem to make sense unless I've misunderstood?

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PhilB
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Re: Full Volume BIAB

Post by PhilB » Fri Mar 29, 2019 10:38 am

Hi Meaty

... it's what Jim said ...

To describe it another way (let's see if that helps clarify :wink: ) , you need to recognise that your efficiency at the end of the mash is as high as it is going to be and from that point forward losses of liquids (containing sugars from the mash) will only reduce your efficiency ... and anything you can do to reduce those losses, either by reducing the volume of liquid lost, or reducing the sugars contained in the liquid lost, can minimise the reduction :?
The particular loss that is different in the two scenarios that you describe is the liquid soaked up in the grains (probably around 0.7-1.0 lts per kg of it, depending on how hard you squeeze your grains) and when you sparge separately the gravity of that liquid will be lower than if you'd full volume BIAB-ed on the same grainbill.

Having said that, plenty of full-volume BIAB-ers find the slight reduction in efficiency, and the slight cost of a little more grain to compensate, worth the convenience of removing a step in the process and the problem of having another body of water that needs heating :?

Cheers, PhilB

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Re: Full Volume BIAB

Post by vacant » Fri Mar 29, 2019 11:11 am

I started AG brewing with a few BIAB brews many years ago and did a theoretcial calculation to see how much extraction I was losing. Turns out I needed about an extra 50p's worth of grain which I was happy with, given the convenience:
Initial assumptions:

1) 35 ltr total liquor
2) 5 Kg of grain in the mash tun
3) when drained the grain retains 5 ltr of wort
4) result is 30 ltr into the boiler

BIAB

Add 35 ltr full volume and do the mash
Once fully saturated 30 of the 35 ltr can be drained i.e 30/35 = 86% of sugars get to the boiler
The wort in the grain retains 14% of the sugars

Two Stage Batch Sparge

Target is to sparge two lots of 15 ltr
Add 12.5 ltr, mash then add a further 7.5 ltr (total 20 ltr) for the first sparge
Once fully saturated, 15 ltr sparged, 5 ltr retained in the grain so 75% of the sugars got to the boiler
25% of the sugar remains in the grain because 5 ltr of wort remains in the grain
Add the remaining 15 ltr to the mash tun, back to 20 ltr liquor
Once fully saturated we can drain 15 out of 20 ltr (15/20) but that wort contains a quarter (5/20) of the sugar so 15/20 * 5/20 can be drained = 19%
The boiler now has 30 ltr with 75% sugar from the first sparge and 19% from the second sparge = 94%
The wort in the grain now retains 6% of the sugars
I brew therefore I ... I .... forget

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Kev888
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Re: Full Volume BIAB

Post by Kev888 » Fri Mar 29, 2019 11:38 am

Yes, as above. If you mash full volume then wort retained in the grains will be higher gravity (i.e. contain more of the sugars) than if the liquid retained was mostly sparge liquor, plus a high quality sparge (not very common with BIAB methods) will encourage more sugars from the grain too. However, full volume mashing is quicker and won't suffer the quality detriment that many forms of rinsing are prone to if not done well. Whilst the cost difference in grain needed could well be insignificant in home brew situations.

People around the web go on about efficiency as if it is some kind of validation of their methods. But it says nothing of the quality, and many of them get their numbers wrong in any case. So IMO it is worth keeping in perspective.

There are some other differences too, the more dilute mash of full-volume affects the enzymes a little, and the alkalinity and perhaps salts would preferably be adjusted accordingly. These are unlikely to have huge impact in many cases, though there might be an argument for mashing at more traditional mash ratios to emulate traditional beers more closely.
Kev

Meatymc
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Re: Full Volume BIAB

Post by Meatymc » Fri Mar 29, 2019 6:05 pm

Ah....................I think I get it!

Basically I've got to compensate for the 'high-gravity' wort absorbed and held in the grain by having more mash water and therefore more grain in the mash - over-egg the pudding as they say?

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Re: Full Volume BIAB

Post by Medarius » Fri Mar 29, 2019 7:00 pm

[quote=Meatymc post_id=842423 time=1553879101 user_id=14557]
Ah....................I think I get it!

Basically I've got to compensate for the 'high-gravity' wort absorbed and held in the grain by having more mash water and therefore more grain in the mash - over-egg the pudding as they say?
[/quote]


Or you can give the bag a good firm twist/squeeze to get the sugars out of the grains.
If you have a false bottom or a way to get bag off the bottom of kettle, bringing the temp up to mash out (74c) for about ten minutes, can help get the sugars to flow more freely also.
But as others have said, a bit more grain can make up the difference just as easy.

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Re: Full Volume BIAB

Post by WalesAles » Fri Mar 29, 2019 10:11 pm

Meatymc wrote:
Fri Mar 29, 2019 6:05 pm
Ah....................I think I get it!
Meaty,
Are you sure?
Are you really sure? #-o

WA

You will get there in the end! :D

Meatymc
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Re: Full Volume BIAB

Post by Meatymc » Fri Mar 29, 2019 11:19 pm

WalesAles wrote:
Fri Mar 29, 2019 10:11 pm
Meatymc wrote:
Fri Mar 29, 2019 6:05 pm
Ah....................I think I get it!
Meaty,
Are you sure?
Are you really sure? #-o

WA

You will get there in the end! :D
Erm...........maybe................or then again :D

By the way WA, I'll have to ask you to hang on for that promised sample - only been a couple of years so far! Very dissapointed with my 1st attempt at a Baby Faced Assissin clone, V2 not looking that much better but brewing V3 tomorrow - let's hope it's worth the wait :wink:

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Kev888
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Re: Full Volume BIAB

Post by Kev888 » Fri Mar 29, 2019 11:30 pm

Meatymc wrote:
Fri Mar 29, 2019 6:05 pm
Ah....................I think I get it!

Basically I've got to compensate for the 'high-gravity' wort absorbed and held in the grain by having more mash water and therefore more grain in the mash - over-egg the pudding as they say?
Yes, in full volume mashing, more grain is needed to make up for the lost/retained wort being of higher gravity and so losing more of the sugars. And a tiny bit more liquor/water is needed to make up for the volume lost to said extra grain.
Kev

Meatymc
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Re: Full Volume BIAB

Post by Meatymc » Sat Mar 30, 2019 9:48 am

Thanks guys

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