Hi there Zelig,

I can't see any problems with your plan. Have a read of this link re diluting high gravity beers.

As for adjusting the hop bill, this will be easier in the new calculator. This has the most accurate hop scaling formulas around. Until it is released, I would use the calculator version I have attached below. From memory, I think this version works okay in metric and US plus it will work out your hop bill almost perfectly (a lot of work by stux on this particular sheet), certainly better than anything else around.

What you'll need to do is firstly type in the original recipe as usual paying particular attention to the original gravity and end of boil volume. I have attached a mock recipe for you using your numbers in the attached sheets.


Zelig 1: I have used a typical 21.3 L into the fermentor recipe. Notice on the hop bill sheet I have put in the average gravity of the original recipe in cell G6. This is a copy of the figure on the right in M6.

So we now have the left and right hand sides of the hop bill sheet matching. You'll also see that I have copied some of the critical values into columns P and Q as we will use them later on. See Zelig 1.

Zelig 2: We now know that we want our diluted recipe to be 27.61 IBU's. IBU dilution is pretty simple. For example, if we had 10 L of wort and diluted it with another 10 L, our IBU's would be halved.

In your case, you will have 13 L going into your fermentor at the end of the boil and you will be diluting it with 5 L. So we simply go... 18/13*27.61 = 38.23. (See Q20 of Zelig2).

So we now know that we want our wort to have a bitterness of 38.23 IBUs. The easiest way to get this reading into M17 is to play around with G5 until M17 reads 38.23.

19.4 L gets us very close (38.18 IBU's)

Now go back to the first sheet...

You now need to work out what OG you need to end up with a diluted wort of 1.050. This formula works the same as the hop formula. You want 1.050 gravity for your diluted wort. This is 50 gravity points so 18/13*50 = 69.23. (See K31 on the first sheet.) So you want your undiluted wort to be 1.069.

The sheet Zelig 2 shows our progress so far.

Zelig 3: In this sheet, I have simply typed in 12.05 into B20 of the first sheet as this number gets us very close to the 13L you want to get into your fermentor from the kettle.

I have then typed in 1.069 for your OG.

Now the recipe is scaled .

It's a bit of a process but one you will get be able to do fairly quickly with a bit of practice.


PP

No problem Zelig. Let us know if anything's not making sense.