Top up with wort?

[Velnerj]

Hello brewing community!

With my brewing system I've hit a bottle neck when it comes to my kettle. It's just a little too small and I know the easiest solution is to get a bigger one. But...

One technique I use in order to maximize volume and still get a high(er) gravity beer is to collect more wort from my mash tun than my kettle can hold by lautering into a separate vessel (usually my bottling bucket). I usually collect about 1 gallon more than my kettle can handle. Then after boil off for 40 min or so there's enough space to add the remaining wort into my kettle.

Let's say I'm making a 1.060 beer after boil and my preboil sg is 1.046. Is there a way to calculate how adding in, say, a gallon of 1.046 wort into 3.5 gallons of 1.060 wort will affect the finishing sg? Or to reverse engineer it so that if I wanted to hit 1.060 with my final version what would the boiled wort sg have to be vs the preboiled wort sg?

I also understand that I could just build my recipes up and top off with water, that's easier to calculate, but I feel my method is less wasteful.

Thanks for any help.

 

[Gnomebrewer]

Yes. (g1 x v1 + g2 x v2) / (v1 + v2) = OG
where g1 is the gravity of wort 1, v1 = the volume of wort 1 etc.
So 1 gallon of 1.046 + 3.5 gallons of 1.060 is
(46 x 1 + 60 x 3.5) / (1 + 3.5) = 55.7
meaning an OG of 1.057

To 'reverse engineer' it, you'd need to know all but one piece of information. eg. you'd need your OG, v1, v2, and g1, to work out g2 (which could be post boil gravity, or top up gravity). That would be
g2 = (OG x (v1 + v2) - (g1 x v1)) / v2
So if you wanted a 1.070 gravity, with 4 gallons of boiled wort, topped up with 2 gallons of second runnings at 1.020:
g2 = (70 x (2 + 4) - (20 x 2)) / 4 = 95
meaning your post-boil gravity would need to be 1.095.

 

[Velnerj]

Yes. (g1 x v1 + g2 x v2) / (v1 + v2) = OG
where g1 is the gravity of wort 1, v1 = the volume of wort 1 etc.
So 1 gallon of 1.046 + 3.5 gallons of 1.060 is
(46 x 1 + 60 x 3.5) / (1 + 3.5) = 55.7
meaning an OG of 1.057

To 'reverse engineer' it, you'd need to know all but one piece of information. eg. you'd need your OG, v1, v2, and g1, to work out g2 (which could be post boil gravity, or top up gravity). That would be
g2 = (OG x (v1 + v2) - (g1 x v1)) / v2
So if you wanted a 1.070 gravity, with 4 gallons of boiled wort, topped up with 2 gallons of second runnings at 1.020:
g2 = (70 x (2 + 4) - (20 x 2)) / 4 = 95
meaning your post-boil gravity would need to be 1.095.

Wow. My brain hurts just looking at it. But honestly after reading it several times I get it. I might just take this formula and put it into a simple excel sheet and create my own little calculator...unless someone else has already done this????

Thanks!

 

[Velnerj]

Ok so if anyone really cares I actually went ahead and made this calculator. It would not be possible without the genius information from @Gnomebrewer Thanks!

....Aaaand for some reason HBT won't allow me to upload an .xlsx file. So if you want it let me know and I can send it to you...

 

[RPh_Guy]

It's a normal blending calculation.

I like the calculator here since it can also do pH:
http://fermcalc.com/FermCalcJS.html

 

[Velnerj]

It's a normal blending calculation.

I like the calculator here since it can also do pH:
http://fermcalc.com/FermCalcJS.html

Well I had fun making my own but where were you 7 months ago? [emoji12]