Extract calculations

Hi,

I confess Im fairly new to brewing, and particularly Brewsmith. However I wanted to learn about predicting brews, not just to follow instructions, starting with extracts and eventually grain.

So, I have this extract brew which claims to be an pale ale the style of which (SNPA) is IBU around 35 and EBC of around 20 :

1.8Kg extract unhopped, EBC 3
1.8kg extract hopped, EBC 7.5, IBU 28
15g Cascade for 15 mins
10g Cluster 15 mins
12g Chinook dry hopped.
23L batch

So off to brewsmith I go :

I partial boil so I set the boil volume to 10L (the max capacity of my pot), and the batch size to 23L - the amount of beer I want to make.

I create myeslf an Extract with EBC 7.5, hop alpha 6.6, 32g for 30 minutes. On its own this gives me IBU 28.
I add the unhopped extract. Then the hops.

But when Ive finished I see the IBU is only 21.8. And the EBC is only 6.9. Quite different from the style the recipe claims to be.

This means either
a) The recipe is wrong
or
b) I dont understand how to use Brewmaster.

Frankly I think the EBC is wrong. Even I can add 7.5 and 3, and its nowhere near 20. Would it be that simple ?

But for the IBUs so I read the help. Search the forums. Read the FAQs. None of that enlightens me, so I play around !

Finally I notice that adding the unhopped extract changes the IBU from 34.8 to 21.8 (and the EBC from 5.5 to 6.9).

So I think, maybe I should increase the hop boil time to 60 minutes. This again gives an IBU of 33.4 - pretty close but dramatically different from the recipe.

But I also notice that the boil volume specified is absolutely critical. Changing this from 10L to 14L also gives me 34.5IBU with the opriginal hop boils recommended.

And so now I realise I really need to understand if Ive added the extracts correctly, that the IBU should drop significantly when I add the unhopped extract and that Ive specified the hop equivalent  for the extract correctly. And I should understand the boil volume (this is the starting total volume when I begin to boil, right ?) as well.

Because if Ive got any of this wrong, Ill end up with a pretty nasty beer ! The original recipe only states it makes 23L, not what the boil volume should be. But given its just an extract recipe I would have thought it was just the two tins of extract and perhaps the same volume of water again. But that doesnt work for the hop boil. Well, not according to Brewsmith.

Am I barking up the wrong tree here ? Please can someone enlighten me ! (dont worry, I wont be touching all grain for quite some time !).

===========

Hi,
  The EBC calculation in your original recipe is probably off - many people calculate the Malt Color units for a recipe and use that as the color which tends to overestimate the actual color.    In addition, as you point out it is unlikely you will produce an EBC 20 beer with two very light extracts unless you use a very large amount of extract.  Here's an article on how BeerSmith calculates the color and explains how to calculate MCU if you want to compare:

    http://www.beersmith.com/Help/colors_tech.htm

  Similarly the IBU calculation depends heavily on which equation you use to estimate the bitterness.  Quite a few recipes use the Rager system because it is quick to calculate, though it tends to produce an IBU estimate on the high side, and does not take into account the full effects of a concentrated boil.  BeerSmith uses the Tinseth equation by default.  You can change it to Rager from the Options dialog (Bitterness page) under the Tools menu if you want to compare calculations.  However, with only a 15 minute boil in concentrated wort, you are probably not getting a full 35 IBUs into the wort.

Cheers!
Brad

Brad,

many thanks for you speedy reply. I hope my amateurish questions arent too tedious ! But Beersmith is certainly helping me understand more....

Wow - changing to Rager gives me 46IBU versus 25IBU for Tinseth. That's a MASSIVE difference that completely changes the recipe from under hopped to over hopped. I admit Im even more confused now as to how to predict the outcome of the recipe. But Im guessing from your comments that Tinseth is the way to go, which will see me adding more hops.

Another critical factor I noticed -  is it right that the predicted IBU is vastly different when I use a boil volume of 10L versus 15L ? This gives me the same bitterness variations as the change from Tinseth to Rager (ie 25IBU (10L boil), 45IBU (15L boil) ie massive ? This would mean that anyone specifying an extract recipe with hop additions must be sure to include the exact boil volume in the recipe or it will be impossible to follow ? And since the recipe I gave doesnt specify this, its effectively useless, (unless of course I trust BeerSmith to predict the IBU correctly for my boil volume and adjust the hopping accordingly.)

many thanks again

Colin

Colin,
  One of the advantages of using a brewing program is that you can take into account many factors like the boil volume - which has a very large effect on hops utilization.  As you point out extract recipes are very dependent on equipment and processes used - more so than all grain brews which typically are always full size boils.

  Personally, I would recommend when starting with an extract recipe from a book you should also look at the style guide to see if the recipe is within the normal range for that style.  Then you can use BeerSmith to adjust.  I think you will find that the overall quality and balance of your brews will improve!

Thanks,
Brad