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OG from 15 Litres to 23

Post #1 made 13 years ago
by ynotnamlac
If I use the no chill method and use my 15 litre cube, and want to add 8 litres of water when fermenting to get to 23 litres, how do I calculate the OG at 15 litres which is required to add 8 litres and reach my required OG for 23 litres? Is there a problem with doing that?

Post #2 made 13 years ago
by PistolPatch
That should be fine but try not to dilute with more than 8 litres. If you have crappy tap water, consider giving it a boil first. If it tastes okay, don't worry.

To calculate the OG you'll need, let's say you want to end up with 23 litres at 1.052. This mean you need 1,196 gravity points in your brew (23 x 52).

So, you'll need to aim for the 15 litres having a gravity of 1.080 (that's 1,196 / 15).

Hope that makes sense!

Edit: Another way to get to this as Yeasty points out below is 23L / 15 L * 52 = 79.7 (i.e. 1.080)
Last edited by PistolPatch on 09 Dec 2012, 19:56, edited 1 time in total.
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Post #3 made 13 years ago
by Yeasty
First abit about dilution..

The formula for dilution is:

Specific gravity/desired specific gravity*volume = volume required

You then have to take your original volume off this figure to give you the amount to add to the FV. So if you had 15L of 1.070 beer and you wanted 1.045 the workings are:

70/45*15 = 23.33L

Minus the original 15L = 8.33L to be added.

:o :lol: I just picked those numbers out of the air and it nearly answers your question :headhit:

We can now transpose this equation to give us what you want..

So you want 23L, your cube is 15L and you want an OG of 1.045.

The formula is:

Post dilution Volume/Pre dilution volume * Desired gravity = Target Gravity

using the above figures:

23/15*45= 68.99

So your target gravity for 15L is 1.069 (rounded)

:salute:

Edit: Beaten by PP :idiot: and by a more simple answer :o
Last edited by Yeasty on 09 Dec 2012, 19:09, edited 2 times in total.
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Post #5 made 13 years ago
by porchfiddler
I had to calculate something similar the other day when I didn't leave enough wort to take an OG.
My hydrometer was sitting on the bottom of the glass, so I topped it up with ~10 % tap water until it floated. My fake OG was 1.042. So my ~ real OG ended up being

1.042= (0.9x)+ (0.1*1.000) Measured OG = (90% of unknown OG)+ (10% of the sg of water 1.000)
1.042 - 0.1 = 0.9x
0.942 / 0.9 = ~1.046

I hope this is correct and please tell me the correct answer if it is not! This stumped me for a little bit as I'm no maths wiz but I hope it might help somebody else down the road who makes the same mistake. The OG was also what I expected which helped confirm it.

Cheers

Post #6 made 13 years ago
by Yeasty
porchfiddler wrote:I had to calculate something similar the other day when I didn't leave enough wort to take an OG.
My hydrometer was sitting on the bottom of the glass, so I topped it up with ~10 % tap water until it floated. My fake OG was 1.042. So my ~ real OG ended up being

1.042= (0.9x)+ (0.1*1.000) Measured OG = (90% of unknown OG)+ (10% of the sg of water 1.000)
1.042 - 0.1 = 0.9x
0.942 / 0.9 = ~1.046

I hope this is correct and please tell me the correct answer if it is not! This stumped me for a little bit as I'm no maths wiz but I hope it might help somebody else down the road who makes the same mistake. The OG was also what I expected which helped confirm it.

Cheers
Your correct mate :thumbs:

Working from percentages the equation is

100% volume/90%volume*known gravity = undiluted gravity

100/90*42 = 46.66666666666666666666666666666666666666 ;)
Last edited by Yeasty on 09 Dec 2012, 20:34, edited 2 times in total.
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Post #8 made 13 years ago
by Yeasty
porchfiddler wrote:I got the recurring 666666's too but as 1.046 was the gravity I was aiming for I ignored them!
Brewing science at its best :lol: :lol: To read .6 on a hydro takes some doing, you were correct in dropping those 66666's ;)
Last edited by Yeasty on 09 Dec 2012, 20:44, edited 2 times in total.
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Post #10 made 13 years ago
by PistolPatch
ynotnamlac wrote:If I use the no chill method and use my 15 litre cube, and want to add 8 litres of water when fermenting to get to 23 litres, how do I calculate the OG at 15 litres which is required to add 8 litres and reach my required OG for 23 litres? Is there a problem with doing that?
Thanks for this thread ynotnamlac. It helped us get BIABrewer to give us A Glimpse of the BIABacus :party:.

If you download the BIABacus from there, in the Maxi-BIAB Adjustments section (towards the right hand side) you'll see a field called, "Water Added to Fermentor.' If you write your recipe into the BIABacus and put 8 litres into that field, all the maths will be done for you automatically. Even your hop adjustments will be changed!

:peace:
PP

P.S. I am trying to get your nickname. I get the ynot bit but is there something more to it I'm not seeing? :think: ;)
Last edited by PistolPatch on 23 Dec 2012, 22:10, edited 2 times in total.
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