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WildIslandBrewer

How to calc Extract IBU's in Brewtarget - doesn't add up

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Hey all - new here - but have been brewing for a few years now, wanting to get more science into my recipes.

I'm trying to get BrewTarget to add Extract IBU's to my recipes.  Coopers list their extract packaged IBU's and say to divide it into the batch volume to get the real IBU.  Same for their colours too.

So using Mr Beer NW PA and nothing else - it's 1.3kg, IBU 390 to make 8.5L batch - I do 9.5L   When you divide that out : 1.3/9.5 * 390 = 53.  However BT calcs this as 6.4 IBU.  The BT entry field for IBU says the figure entered should be the bitterness of the pre-hopped extract but I'm unclear on the units.  Nothing I use seems to make sense.

Any ideas.  TIA

 

Edited by WildIslandBrewer
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Just enter the 390, see how it comes out. And welcome to the crew.

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Ibus×weight then divide by volume. (390×1.3)/9.5 liters or whatever batch size you do so the 53 is correct.  I would try what Titan said or ignore it as you know the IBUs. Are you adding any other hops?

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The Coopers formula makes sense and should give 53 but is that what I get in my glass??  This is the only calculation that makes any sense.  I have 3 other formulas to convert SI to  the seemingly stupid ibu*lbs/gal and they are inconsistent.

I just want to understand how BT gets 6.5 so I can get a picture - for my tongue!

 

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I totally understand, my only guess is they have a calculation wrong in the backend someone and it is feeding through incorrectly.  I had issues with beersmith and I used Ian's spreadsheet to try to work out the issue. That helped.

The only other thing is to make sure you entered everything right but besides that, I got nothing.

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53 is the pre fermentation figure. After fermentation it drops by 10-30%, so it will be anywhere from about 35 to 48 (roughly) in the glass. 

As for that program I have never used it and know nothing about it.

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Otto (dunno yet how to tag) BT is a bit like BeerSmith but it's open source and free.  Free for me is not the point - coming from a past computing and IT era I don't like subscription and/or cloud software as IMPO it's a business risk just waiting to happen.

After much reading and head banging I have some info.  Apparently this IBUs setting was a problem in BeerSmith too.

The Coopers figure is the total of AA's in the can so it's meaningless if the weight is not normalised, giving a AA count per a particular weight.  This is what the Coppers calculations do - convert it to AA's per Litre of beer.  First, you must convert the Coopers can IBU number back to a 1Kg amount.  Some cans are 1.3Kg, some 1.7Kg and (I read in NZ) some 1.8Kg. 

So a 1.3Kg Mr Beer NW PA at 390 IBU is 300 IBU/Kg but a 1.7Kg Coopers Lager at 390 IBU is 229 IBU/Kg.  

If we look at the final batch IBU using the Coopers calculation, the Mr Beer NW PA is 1.3 * 390/8.5 = 59.65 IBU.  

The total AA's in the batch has to be adjusted for losses too.  So if you lose 1L in your brewhouse, the total AA's from the can are spread out over 9.5L of beer.  I don't know if BT (or BS) adjust for these losses.  If it doesn't then the end IBU's should match the Coopers calculations.  If it does then your end IBU will be lower. 

To enter these into BT you need a normalised IBU/Kg and a scaling figure that takes into account the US IBU calcs used and (possibly) the brewhouse losses.

The BT (and BS) figures are in US IBU * Gal/Lb which is a fixed bitterness 'count' in the same style. as IBU  Just gotta determine now how BT does it's calculations.

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There aren't any losses in kit/extract brewing. You just mix up the extract in a known volume of water and there's your batch of wort. If it's 8.5 litres then that's the volume the IBU calculation is done with. 

I've never used beersmith for extract brewing so I don't really know what it does in that instance or how it calculates whatever. I only got it after I went to all grain, which it has been really good for.

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@Otto Von Blotto (tks @NewBrews !) 

I leave about 1/2-1L in the fermenter, depending on how much crud is in it.  That the loss I was thinking about - either the batch is smaller and IBU is right or dilute the batch a bit to compensate.  I use 9.5L kegs so a ferment is generally 10L. 

When I'm playing recipes I want to be able to get an IBU throughout the software that I know is close so I can compare tastes to other beers - without spinning up a batch.  And currently BT is out by 10:1 using Coopers' figures and the US formula.   I know why they are out but not how to fix them yet - with science, not just back-calculations.

 

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Yes that bit is lost but the IBUs are calculated by the total volume in the fermenter at the start. If you make it to 10 litres you use that, which basically makes the losses irrelevant. 

The calculation is IBU X kit weight ÷ batch volume. The volume for this isn't set in stone at 8.5 litres (or 23 litres for the bigger kits), you just use whatever it is that you make it up to. 

That one of 390 in the kit made up to 10 litres would be 50.7 IBUs before fermentation. 390*1.3÷10.

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Beersmith has a Coopers Add-on that you download.  It has the various parameters for the cans.  As noted above it requires a Gal/Lb value for bitterness.  Unfortunately, the add-on just shows the "in can" IBU's so when you add a Coopers can to a recipe it shows wildly nuts final IBU's.  After some head scratching and trial and error I came up with an adjustment of the in-can IBU on the Coopers website and now my Beersmith Coopers recipes come out more like the IBU's of the finished recipes on the Coopers website.

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@Shamus O'Sean do you find it accurate across different coopers cans?  I did a similar thing and worked back a correction but if I correct for a eg MrBeer can, for a Lager can it's about 10% out.  This was using the ibu/kg figure.

I then created a fake hop variety to see how that works rather than hopping the extract.  I set it up so you enter the can ibu/kg as the hop weight and then back-calculated the AA content to give the right end ibu.  Again it differs across cans.  It's probably close enough but I'd like to get it right.

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