Calculating IBUs

I don't know if I have a setting incorrect or just don't understand how BS calculates IBU's.  Here's the story:

My next brew is a Russian Imperial Stout.  I have two hop additions.  A 60 minute: 2 oz. Magnum @ 14% AA which, on the ingredient list says contributes 93.3 IBU.  Then a 3 minute addition: EKG @ 5% AA, which according to the list contributes 8.3 IBU for a grand total of 101.6 IBU.

However, down on the style slider it has calculated 65.2 IBU, which is what I want.  Which is correct?  Why are they so different?  Do I need to fix something?

Thanks, Steve

"a 3 minute addition: EKG @ 5% AA, which according to the list contributes 8.3 IBU"
When I add this to Beersmith I get 2.1 IBU for the addition.  Are you sure you want to go with 2 oz of Magnum??  That already puts you over the style guidelines.  Can you post your recipe??  There are a lot of AG brewers at the Beerborg you may be able to help you out too.

Thanks for your reply.  Yes that is why I am asking the question.  here is the recipe:


St. Dimitri of Rostov RIS

Imperial Stout (13 F)

Type: All Grain
Batch Size: 5.50 gal
Boil Size: 7.50 gal
Boil Time: 60 min
End of Boil Vol: 6.50 gal
Final Bottling Vol: 5.50 gal
Fermentation: Ale, Single Stage

Brewer: Steve Harrison
Asst Brewer:
Equipment: A My 5 gallon
Efficiency: 75.00 %
Est Mash Efficiency: 85.2 %
Taste Rating: 30.0

Ingredients

16 lbs Pale Malt, Maris Otter (3.0 SRM) Grain 1 77.1 %
1 lbs Barley, Flaked (1.7 SRM) Grain 2 4.8 %
1 lbs Caramel/Crystal Malt - 60L (60.0 SRM) Grain 3 4.8 %
1 lbs Roasted Barley (300.0 SRM) Grain 4 4.8 %
1 lbs Wheat Malt, Ger (2.0 SRM) Grain 5 4.8 %
12.0 oz Carafa II (412.0 SRM) Grain 6 3.6 %
2.00 oz Magnum [14.00 %] - Boil 60.0 min Hop 7 61.1 IBUs
1.00 Items Whirlfloc Tablet (Boil 15.0 mins) Fining 8 -
0.50 tsp Yeast Nutrient (Boil 15.0 mins) Other 9 -
3.00 oz Goldings, East Kent [5.00 %] - Boil 3.0 min Hop 10 4.1 IBUs
2.0 pkg Denny's favorite (Wyeast Labs #1450) Yeast 11 -


Gravity, Alcohol Content and Color

Est Original Gravity: 1.104 SG
Est Final Gravity: 1.026 SG
Estimated Alcohol by Vol: 10.4 %
Bitterness: 65.2 IBUs
Est Color: 38.7 SRM

Measured Original Gravity: 1.046 SG
Measured Final Gravity: 1.010 SG
Actual Alcohol by Vol: 4.7 %
Calories: 151.6 kcal/12oz

I just noticed the above copy of the recipe shows the same IBU as the slider.  So why, when I open the file does it say 93 IBU rather than the 61 listed above?

If you attach the .bsmx file we can take a look and maybe help identify the discrepancy. I've seen in the past, when messing around with the types and amounts of hops and malts, moving them around or substituting, that the final IBU numbers can get screwy. If I've messed with one recipe enough, I'll take the ingredients and amounts I've come up with and build a new recipe with them and lo and behold; different IBUs! Not sure how to explain it, but I've seen it so I know it happens.

It took me a while to figure out how to do this.  That and I have been gone for a few days.  Anyway, attached is the file.  Your input is appreciated.

Steve

When I open your bsmx file on my Beersmith, it shows 61.1 IBU's for your 60 minute Magnum addition in the ingredients list.

What you described didn't duplicate for me.

I would suggest having your beersmith program not launched and click on your bsmx file here in the forum and let it open your BeerSmith that way and see what it does.

Did you open it all the way?  When I download the file and look at it on the preview pane it shows 61.1 IBU, but when I open it all the way up it shows the 93.3.  Obviously I can live with 61 but not the 93.

I'm thinking that you're seeing the results of two different calculations. I believe you are seeing Rager's calculation as the high number and perhaps Garetz as the lower. IBUs in homebrewing are an estimate because so many parts of your process can add or subtract actual IBUs.

With a RIS at 1.100, you can stand the 93 IBus. You probably won't actually get that much and you likely can't taste it, either. But, RIS can be very sweet if it's under bittered.  Even at 61, it's still a solid IBU number for the style.

I think you'll be ok.

I'm seeing 61.1 for the Magnum addition.

Your BS setup plays a big part in determining what you see in the sliders and in the recipe. If you are set to Rager, you'll see 93.3 instead of the 61.1 most of us are seeing - we're set to Tinseth. Looks like brewfun nailed it.

The only place where this can cause confusion is when you share recipes - the user needs to know what method was used to calculate the bitterness. Doesn't really matter what method you use for the calculations, pick one you like and stick with it. BS defaults to Tinseth, at least mine did, and I've never changed it. Some recipes come from brewers that worked in other units so if something doesn't look quite right, try changing the calculation method to see if it snaps back into place.