BIAB Volumes

[chrisstuarthall]

Hi all

I am about to start both partial and full mash brewing.

I have been reading various books and watching YouTube videos and one thing puzzles me.

For an all grain BIAB 23 litre recipe why do you start with say 27 litres to achieve the final brew length?

Why cannot you mash, sparge and boil with less liquid making up the volume to 23 litres with water at the end?

:hmm:

 

[MyQul]

Why cannot you mash, sparge and boil with less liquid making up the volume to 23 litres with water at the end?

:hmm:

You can, in fact you can make bigger brew length than your pot can hold (e.g do a 23L/24L brew length with a 20L pot, its called Maxi BIAB

http://biabrewer.info/viewtopic.php?t=352

 

[StrangeBrew]

For an all grain BIAB 23 litre recipe why do you start with say 27 litres to achieve the final brew length?

I find I use about 30~31 litres to cover for grain absorbtion and boil off. A 50 litre pot works out fine allowing enough headroom (30 litres plus the grains volume !) and minimising boil over risks.

Why cannot you mash, sparge and boil with less liquid making up the volume to 23 litres with water at the end?

You can and it's called Maxi BIAB as mentioned, although personally I havn't tried it.

 

[rodwha]

It's better not to use top off mostly due to hop utilization. If you created 30 IBU's but then added 1/3 top off water you now have ~20 IBU's. So you maximize your hop utilization by doing a full boil. Or you can use more hops and target 45 IBU's to bring it back down to ~30.

 

[chrisstuarthall]

Thanks rodwha...I use Brewers Friend to calculate quantities.

As long as I use a standard 23 l brew length in the calculations and the predicted quantities, then if I go under on the boil, topping up should give the calculated results.

I understand that now, thanks again.

 

[MyQul]

It's better not to use top off mostly due to hop utilization. If you created 30 IBU's but then added 1/3 top off water you now have ~20 IBU's. So you maximize your hop utilization by doing a full boil. Or you can use more hops and target 45 IBU's to bring it back down to ~30.

So is topping off water and IBUs like for like percentage wise? so if I top up say 27% I need to increase my IBUs by 27%?

In your example above, 30 IBUS with 1/3 top off water brings you down to 20 IBUs but in the second part you say target 45 IBUs to bring you back down to 30. Shouldn't that be 40IBU's or am i missing something (i probably am as I'm hopeless at maths)

 

[rodwha]

The way it was explained to me by a moderator of the American forum I'm a member of was in fractions, and done in a simple matter by showing half. I may have misunderstood, but this is how I took it.

So if the target is 30 IBU's but I'm using 1/3 of my volume as top off water I'd need to shoot for 45 IBU's since dividing 45 by 3 gives 15, and so I'd need to reduce the overall (45) IBU's giving 30.

 

[MyQul]

So if I say am aiming for 26IBU, I divide it in half to give me 13 and add that to the overall total to give me 39?

Edit: I'd prefer if you could answer the one below if you don't have time to answer both as I'm doing a Maxi-Biab next week

 

[MyQul]

When I do A maxi - biab I usually get about 17L which I then dilute up to the full 23L. 17/23 comes out at 26.1%.

Rounding it down to 1/4 for ease if I was aiming for say 30IBU how much more hops would I need to add? :wha:

(God I hate maths)

 

[rodwha]

If 30 IBU's is your goal and you are topping off with 1/4 plain water you'd need 40 IBU's to begin with since 40/4=10, which is what you'd subtract from the 40 initial IBU's which gives you ~30 IBU's.

I'm not sure how accurate the dilution makes it, but it's what I'm told…

Another reason to push for full boils I suppose! For me that would mean I'd need to reduce my end volume though, which I don't really want to do.

 

[MyQul]

If 30 IBU's is your goal and you are topping off with 1/4 plain water you'd need 40 IBU's to begin with since 40/4=10, which is what you'd subtract from the 40 initial IBU's which gives you ~30 IBU's.

I'm not sure how accurate the dilution makes it, but it's what I'm told

Another reason to push for full boils I suppose! For me that would mean I'd need to reduce my end volume though, which I don't really want to do.

So 40/4=10 but how did you come up with the ten in the first place?

I cant do a full boil as I've only got a 20L pot

 

[MyQul]

Mmm. I think the mists are finally clearing.

Thanks for all the help with this. When I first started doing Maxi -Biab I did a couple of Enlish Pale Ales (Youngs Special and London Pride) and they turned out a lot sweeter than they should have been. I figured out I hadn't go as good a hop utilization as I should have but but couldn't work out where In the process I was getting the lower hop utilization. This thread has cleared it that up form :thumb:

 

[MyQul]

Have discovered a dilution calculator on my brewmate software. So this'll save my brain aching