Calculating OG change when performing a boil down.

[vibroluxious]

I have searched for info on calculating this and haven't found any real information.
If I boil down a gallon of first runnings to 1 qt then add it back to the boil, how much of an increase would I see in the OG?

First time I've ever had to ask a question.
Search works really well.

My assumption is that I can calculate the change in gravity from 1 gallon to 1 quart but I'm not sure how to calculate the change in the wort overall when it's added back in.

 

[BroStefan]

Easy.

Let's say you have 1 gal of 1.050 wort. Ignore the 1 and you have 50 gravity points per gal. Reduce the volume to 1/4 of the original but you still have 50 gravity point in 1 quart and a sg of 1.200!

(Gravity points * original volume) / final volume = sg of final volume.

 

[vibroluxious]

That part I pretty much had down. If I add that 1.200 back into a boil of say 6.5 gallons at 1.050, how do I calculate the change to the boiling wort.

I'm working on an Old Ale recipe and trying to calculate the estimated OG.

 

[BroStefan]

Ok, got it

The concept is the same. At the beginning of the boil you have a certain number of points available. Say 50x 6.5 gals = 325 gravity points.

When you pull a gal and boil it down you just reducing the volume thus increasing the sg. (Your getting flavor development as well, but that's not a factor here)

When you add it back to the main boil you still have the same total gravity points in whatever volume = your SG. By splitting your boil you'll increase volume reduction but the total available gravity points are constant.

 

[vibroluxious]

That makes sense. I had been trying to back into it by reversing a dilution calculation then calculating the OG from that point. I was showing an increase of about .05 gravity points by backing into it. You are correct that I am doing the boil down for flavor reasons.
Thanks for the assist.

 

[Minky]

That part I pretty much had down. If I add that 1.200 back into a boil of say 6.5 gallons at 1.050, how do I calculate the change to the boiling wort.

I'm working on an Old Ale recipe and trying to calculate the estimated OG.

It's the same equation that BroStefan used in his original example:

Gravity x Orig. Vol. divided by Final Vol.

The difference here is you're adding two solutions together, so you do it like this:

6.5 gal. x 50 divided by 6.75 (adding your qt., or 1/4 gal. makes final vol. 6.75) = 48.15
.25 gal. x 200 divided by 6.75 = 7.41

Add the 48.15 and the 7.41 together and you get 55.56 or a gravity of ~1.056


EDIT: I think I may be doing something different here. Are you saying that the gallon that was boiled down came from the original 6.5 gallons?

 

[vibroluxious]

Minky, you had it right. Using the method I was using, I came up with the same number as you. I was over thinking it.

Thanks for showing me a MUCH easier way guys...

 

[Minky]

Minky, you had it right. Using the method I was using, I came up with the same number as you. I was over thinking it.

Thanks for showing me a MUCH easier way guys...

Yeah, I'm sure there are different ways to set up that sort of a calculation, but my brain needs the easiest way. By the way, it's that algebra we swore we'd never use after high school!

Now, go crank up that Vibrolux! :rockin: