IBU changes when I change from Boil to FWH. Why?

[Yooper]

We are changing the IBU calculations right now, and it will be more in line with the current thoughts- that is, IBUs of the boil time + 10%. I'm unsure today as to whether or not the brewer can change that utilization factor himself. It's being tested now and I'll keep you informed!

 

[KC]

IBUs of the boil time + 10%

Do you have a source for that formula? I did a brief look this morning but haven't read into it in over a year. Somebody must have done an IBU lab test by now.
I would expect that both mash-out temp and time between wort addition and boil point are all factors along with overall boil time. Currently, the recipe calculator doesn't use those variables for anything.

 

[GFHomebrew]

I did a FWH and A 90 min boil on last brew fermenting ATM so will get a good idea of bitterness from FWH from this.

 

[Yooper]

It's the "standard" formula used by most people/software that I know of. I have no idea where the "20 minute" thing came from initially, except for a (some say flawed) German paper in the 1990s.

I've done FWH and non-FWH beers side by side, and there is no way a FWH beer tastes like a beer with the same hops added at 20 minutes. Yes, it's a "softer" bitterness, but no 20 minute flavor hops are detected.

IBUs are a function of temperature and time. Hops boiled for 60+minutes will have much of the hops oils isomerized. For a non-sciency, but very interesting little experiments/reads:

https://www.homebrewersassociation.org/how-to-brew/what-is-first-wort-hopping/
http://byo.com/cider/item/2958-pre-boil-hopping

 

[GFHomebrew]

Cheers for the helpful info yooper I'm going to FWH sazz in my up coming wheat beer my IBUs for my FWH addition come to 11 IBUs Including my 20 min sazz addition. From this information maybe I should just increase my FWH additiion and not worry about flavour addition at 20min as the FWH should technically be contributing to this anyway.

 

[Yooper]

That hasn't been my experience- I haven't noticed that FWH replaces flavor hops. I don't know where the "20 minute" addition idea came from, except from that flawed German paper. I use FWH a lot, but I still use flavor hops if the beer is suited to them.

 

[GFHomebrew]

That hasn't been my experience- I haven't noticed that FWH replaces flavor hops. I don't know where the "20 minute" addition idea came from, except from that flawed German paper. I use FWH a lot, but I still use flavor hops if the beer is suited to them.

Ok cheers the oils released in mash should contribute to flavour though ? I also checked what the ibu contribution from hop would be at 60 min boil and it was 20 IBU + 10%'for FWH so going buy that real IBUs should be just above 21ish IBUs For FWH going buy information in them Papers? Below is recipe for FWH
http://www.brewersfriend.com/homebrew/recipe/view/425369/lemongrass-wheat