Confused IBU calculations

[bowlerhatman]

Hi there,
I've been making Italian APAs lately, and I've come across something weird. I was hoping someone could help me understand what's happening.

The recipe I have claims 42IBU. It has a target volume of 23L and a target OG of 1.070. The hop schedule is:

5g magnum, 12.5% @90min
10g columbus, 12.2% @45min
30g Amarillo, 8% @0min
20g Cascade, 5.5% @0min
10g Amarillo, 8% Dry hopped

Whenever I try to calculate this (usually according to the Tinseth formula) I get about 18IBU, clearly not a minor error. I have done this both on paper and using online calculators. Initially I thought it was a recipe error, just because the calculations were so consistently out. But then I had a friend measure the IBUs. It wasn't a perfect procedure that he used, but he read 40IBUs from a sample. Clearly closer to the recipe than the maths.

All I can think of is that the dry hops and flameout hops are contributing bitterness, but that the maths doesn't account for it.

I no-chilled this one, so there would have been higher hop utliisation than if I had chilled it, but surely not enough to add an extra 20IBU...

Any help or insight would be much aprpeciated!
Thanks,
Bowler.

 

[Dan Pratt]

The dry hop adds no bitterness, only perceived through flavour and aroma that it's hoppy......The 0mins addition will add bitterness, unlike the 90 and 45min additions that are noticeable of the palette as a bitterness it will be or perceived again as bitterness but more flavour than actual bitterness.

 

[Burt de Ernie]

Italian APA?

What is different to a regular APA?

 

[NewtownClown]

Brewed in New Jersey, perhaps.

 

[bowlerhatman]

Brewed in Italy, in fact. It's the Open, made by Open Baladin. I can't post a link at the moment, but it's easy to find on the web. It's a good recipe, weird maths issues aside.

 

[bowlerhatman]

@Pratty, that's what I thought, and it's what the maths reflects, but it still doesn't explain the missing 20IBUs.

 

[spog]

Italian micro breweries make fantastic beers....oh the memories,drooling...