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IBU Calculator - what the heck is going on

I have been using the IBU calculator at Brewer’s Friend. I thought I would search for some other calculators because I got some odd numbers from one of the last IPA’s I brewed (the calculated IBU was much lower than the taste). As a result, I did some searching for other calculators. For my most recent brew I just pulled the final gravity - a German Alt (extract kit from NB). I used 6 different calculators online and ended up with 6 different results…and the range is pretty drastic from 33 to 57 - WHAT THE HECK!

Here are my numbers:
Original Gravity - 1.052
Boil Size - 3gal
Final Batch Size - 5.25gal
Hop 1 - AA 7.1 @ 60min
Hop 2 - AA 7.1 @ 45min
Hop 3 - AA 2.2 @ 15min
(all hops are pellets)

From Brewer’s Friend.

From RealBeer.com

From Hopsteiner.com

From Homebrewing.com

From MoreBeer.com

The calculators that are lower account for partial boil/topping off. With partial boil you have a higher concentration of sugars which affects the isomerization of AA. The other 2 do not account for this. Full boils get better utilization of the hops.

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Interesting - makes sense since the two that account for pre-boil volume give results of 33 and 36 (and the others are 40s/50s)

Is it ‘expected’ to get two completely numbers even from those two calculators that account for partial boil/topping off? A difference of 3 isn’t much but it is different.

If I just look at other three (let’s assume I did a full-boil) the numbers still vary by 9 IBUs (which seems like a lot).

You also have to double check that the Alpha Acid that is on your hop package matches what is store in your calculator’s data. The Polaris Hops I just used was 5 lower than what was in my calculator’s data set but still in range for the hop.

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  1. first, you’ll NEVER notice a difference of 3IBUS. If you can you are a super duper taster. IIRC even the best tasters can’t tell the difference between 5IBU difference.
  2. I would expect a difference as each developer will use a similar but different equation on getting their IBUS. For example one might think that you’ll get 100% of utilization from your hops, while another might think you’ll only get 90%.

My advice is to pick a program and stick with it. Brew and see what you have at the end. Then you’ll know if you need to back off on the IBUS or not on the next batch.

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This is what trows me off as well. After creating recipy on paper. I. Transfer this to brewers friend. Recipy creator. Dicede to check. The ibu. With brewers friend. Ibu calculator. Result. End up with. Different. Numbers. So. Me confused. Since i use brewers friend. Software. All numbers. Ibu. Should be the same. ???

I suggest you pick a hop schedule and see how it turns out… If you think maybe a half ounce will make a difference…well then play with it… I doubt you can tell much, if any difference in the late hop additions…
Bittering is different… And to each their own preference… I’m not a fan of very bitter brews… Somewhere in the middle is happy zone…
Take notes and compare is bottom line… The online stuff gets you a starting point…
Sneezles61

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