Calculation dilution volume

[liammiller]

Forgive me if this is obvious or explained elsewhere but I haven't been able to find it.

My boil off rate varies from brew to brew.

Is it possible for me to calculate the amount of post-boil top-up water needed to hit a target OG if I know 1) pre-boil volume 2) pre-boil gravity 3) post-boil gravity?

I don't know post-boil volume, so a target diluted volume isn't useful to me.

 

[Tess Tickle's Brewery]

Does this help?

 

[NotSure]

Forgive me if this is obvious or explained elsewhere but I haven't been able to find it.

My boil off rate varies from brew to brew.

Is it possible for me to calculate the amount of post-boil top-up water needed to hit a target OG if I know 1) pre-boil volume 2) pre-boil gravity 3) post-boil gravity?

I don't know post-boil volume, so a target diluted volume isn't useful to me.

From your three known numbers, you can get the post-boil volume. Once you know the post-boil volume, dilute to hit your target.

I just happened to add a calculator that does this to my site earlier this week: Boil-off and dilution calculator

If you use the second calculator to calculate Volume twice, you should get the number you need. Input the first time (1) pre-boil volume, (2) pre-boil gravity, and (3) post-boil gravity. Then repeat with the numbers it just gave you to find out what volume you need to dilute.