Hop Steep IBU contribution

[The Baron]

You do get isomerisation at lower temperatures, down to about 40C I believe but the rate of isomerisation drops dramatically so for all practical purposes below 60C (4%) can be ignored.

Thats the reason I played devils advocate H. In a previous thread some of the boffins were saying its impossible to get isomerisation but I do know that alright it was not a true experiment but when I have done low temp Whirlpooling with no other additions you do get some bitterness and thats where the perceived bitterness argument started saying it was impossible for isomerisation.
Well I am not a full blown boffin and do listen to some of them as you can get some good info but who do you believe.
I will in summing up add that I am susceptible to tasting bitterness more than most and thats why I have gone down that route of doing a lot of whirlpooling but do standard additions in Bitters/Ales. As you have said for most brewers it is not worth even bothering about at the lower end but as you have pointed out at the higher end of whirlpooling you can get some serious IBU contribution when adding masses of High AA hops.
Personally I think the info on this thread as been good and stands well with what I believe just hope this helps some of the newer members

 

[Hazelwood Brewery]

It’s can sometimes be difficult to get a clear and correct answer to any question because there are so many variables - and so many opinions!

Here is a table showing isomerisation of hop alpha-acids with temperature taken from a research paper. This particular piece of research only looked at 100C, 90C, and 80C but it’s enough to give you an idea - just look at the relative “total iso-alpha-acids” at the three temperatures for a given time (maybe also note the alpha-acids do isomerise but take longer at lower temperatures). I’ve also posted a link to the paper.

https://www.researchgate.net/publication/5255423_A_Kinetic_Study_on_the_Isomerization_of_Hop_a-Acids

 

[dmtaylor]

Here is a decent rough approximation. Source is me. Call it the Taylor equation if you want... or don't, I don't really care. I'll even convert it into grams and liters for you. Please, play around with it, see what you think. I'll listen to feedback. Maybe I need to increase the 7.5 1.5 divisor, the result certainly being only good to about one significant digit, not really two digits. It's an estimation, which I think is reasonably accurate, and better than nothing.

https://www.thehomebrewforum.co.uk/threads/hop-utilisation.97728/#post-1111237
or:

IBU = grams * AA% * sqrt(2*HStime) / V / 7.5 1.5

where
V is post-boil volume in liters,
Boiltime is in minutes, and
HStime is post-boil hop stand time in minutes where it hangs around between about 65-90C.

By the way... Isomerization doesn't magically quit at 80C. It's just quite slow below that point. There's still isomerization happening down to like 60C or thereabouts.

Cheers.

****, I screwed up my conversion factor from USA units to SI units. The 7.5 should be a 1.5. Expand above to see the corrections. Really sorry about that -- and I used to think I was kind of good at math!

 

[hoppyscotty]

Think all IBu calcs are inaccurate and ‘for indication purposes only’ it seems. Seen several pro breweries saying the advertised bitterness of their beers in IBU’s based on recipe calcs turn out to be very different to reality when they send a sample to a lab to measure the actual IBU’s.

My assumption is you do pull IBU’s through the hopstand, and through cooling as it takes a good 40 mins to cool the wort. Which is why I limit my hopstands to no more than 15 mins and no more than 75 degrees as I’m after hop flavour over bitterness and don’t want to lose the hop flavour through evaporation during the steeping.

Ultimately does it really matter what the actual number is? Use the ibu calcs in recipe development to get a beer in the ball park of your desired bitterness and if the results get you there then great, if not then adjust the recipe. Many other factors come into play around consistency of your process, environment of your brewhouse etc. so not just all about the theoretical result based upon the mathematics. That is just one element in many that impact the end result.

 

[dmtaylor]

****, I screwed up my conversion factor from USA units to SI units. The 7.5 should be a 1.5. Expand above to see the corrections. Really sorry about that -- and I used to think I was kind of good at math!

****... I was right the first time. It really is 7.5. Ugh, I am disgusted with myself now. Ignore the idiot, I'll be on my way now.