# Homebrewers Association | AHA Forum

## General Category => General Homebrew Discussion => Topic started by: flapjack on August 14, 2010, 02:16:18 AM

Title: Calculating IBUs
Post by: flapjack on August 14, 2010, 02:16:18 AM
We have been shifting from developing our beer recipes on hopville to calculating them ourselves. Since we have been doing this we have been hitting our targets almost exactly but cant figure out if the IBUs are correct. We are working on a 5.5 gallon Belgian Dubbel recipe and according to Hopville the IBU's are 23.5, using 3 oz. Stryian Goldings 5.2AA, 1oz each at 60, 45 and 30. When calculating it on our own we are coming up with 52.684 IBUs using a HOP UTILIZATION(HU) of:
(oz x AA x HU)     / (final volume x 1.34 [constant # from Joy of Hombrewing?])
60min = 30% (1 x 5.4% x 30%) / (5.5 x 1.34) =  21.98
45min = 24% (1 x 5.4% x 24%) / (5.5 x 1.34) =  17.584
30min = 18% (1 x 5.4% x 18%) / (5.5 x 1.34) =  13.12
=  52.684IBUs

What are we doing wrong?
Title: Re: Calculating IBU's
Post by: tygo on August 14, 2010, 02:27:10 AM
What is your projected boil gravity? Your assumed utilization looks high; where are you getting it from?
Title: Re: Calculating IBUs
Post by: flapjack on August 14, 2010, 02:42:34 AM
Projected gravity of boil is ~ 1.63. Getting the utilization from the chart in The New Complete Joy of Home Brewing pg.268

Approx. Specific Gravity of Boil 1.070, 30min 14% 45min 24% 60min 27%. seems like we are a little high but not to be off by ~2:1
Title: Re: Calculating IBUs
Post by: tygo on August 14, 2010, 03:25:52 AM
Putting that into Beersmith and using the Tinseth scale I get 36 IBUs which is also close to what I get doing it by hand based on the methodology that Palmer shows:

http://www.howtobrew.com/section1/chapter5-5.html

The utilization chart shows that a 60 min addition to a 1.070 boil yields a utilization of 19.3%.  I don't have my copy of Papazian's book handy so I'm not sure what you're seeing there.
Title: Re: Calculating IBUs
Post by: brushvalleybrewer on August 14, 2010, 12:20:20 PM
We have been shifting from developing our beer recipes on hopville to calculating them ourselves. Since we have been doing this we have been hitting our targets almost exactly but cant figure out if the IBUs are correct...

What are we doing wrong?

Welcome to the club. I’m making my own spreadsheet, too. It’s a great learning experience.

When you say your IBUs are not correct, what do you mean?

Do you mean that you had your beer measured in a lab and the calculated value is different from the measured value?

The first thing to know is that all methods for estimating bitterness are just that: estimates. Estimates use assumptions. Different people make different assumptions. The AHA has a nice article called "What’s Your IBU? (http://www.homebrewersassociation.org/attachments/0000/2501/IBUs.pdf)" that goes through some of the more popular methods for estimating IBUs. Some are more accurate than others. Some are more popular, even though they may be less accurate. I use Rager. It seems that tygo is using Tinseth. We will get different answers.

It looks like hopville (http://beercalculus.hopville.com/recipe) uses Tinseth by default, but you may have changed it to something else.

Do you mean that the value you calculate does not match the software you use?

It looks like you are using a formula from Papazian’s Book. Is that the same method your software uses? If not, it is understandable that they do not agree.

As a home brewer, the key is to consistently use one method so that you learn what to expect. If you change what formula you use, you’ll get different numbers and they won’t mean anything to you.

Do you mean that it does not taste right?

IBUs do not directly correspond to taste in beer. They are an estimate --- or sometimes a measure --- of the amount of isomerized alpha acid in the boil. Those do taste bitter, but there are other things in beer that also taste bitter. Sometimes stuff in the boil doesn’t make it into the beer. Also, there are things that affect the perception of bitterness. Water chemistry (http://brewery.org/library/wchmprimer.html) plays a role. You mentioned that you are considering boil gravity. There is some discussion that final gravity has as much to do with our perception of bitterness and some suggest using a “balance value (http://beercolor.netfirms.com/balance.html)” instead of a bitterness value as being a better predictor of hop impact. Still, bitterness is only one dimension of the hops contribution to the flavor of beer.

Do you mean you’re having trouble with the math?

Like tygo, I suggest you find some brewing software and let it do the math. There are many popular applications for PCs and Macs. A quick search for “brewing software (http://www.google.com/search?q=brewing+software)” should turn up quite a few. Some are free or come with a free trial period.

When it comes right down to it, it is hard to encapsulate all of the wonderfulness of hops in beer into a single number. Don’t be surprised if you find it lacking.

Happy Brewing!
Title: Re: Calculating IBUs
Post by: Malticulous on August 14, 2010, 03:53:52 PM
All too often I see Hopville recipes with the average boil volume set improperly. It has a huge impact. I set the batch size to 5.5, OG to 1.064, the average boil volume to 6, use pellet hops (pellets have 10% more AA by weight) and get 46.4 IBU with Tinseth.
http://hopville.com/recipe/309467/home-brew/ibu
I'd like to see your recipe. I use Hopville exclusively.
Title: Re: Calculating IBUs
Post by: Malticulous on August 14, 2010, 04:12:16 PM
http://hopville.com/recipe/301583/belgian-dubbel-recipes/pig-dubble
I think I found it. And unless your doing a partial boil of about 3.5 gallon it's set wrong. When I change it to 6 average gallons for the boil it comes to 42.8 IBU. If you start with 6.5 gallons and end up with 5.5, 6 would be the average. If you have more boil off it would need to be higher.