Mid Boil Hop Additions

[Sorcerers Apprentice]

Someone asked about the advantages or not of mid boil hop additions, at the conference day, and I felt it wasn't answered by the panel.
In the past in my old job, we added all of our hops at first worts as we filled the kettle and later the EBUs were fine tuned by the addition of post fermentation bittering hops. The hop utilisation of the post fermentation bittering is much higher but they are far more expensive and there are maximum addition limits above which a harsh taste can be detected in the beer.
A decree came from above to investigate hop utilisation in kettle, with trials adding different percentage of the hop bill at various stages of the boil, and the corresponding EBUs were evaluated post fermentation. A longer boil can have a negative effect on utilisation, contrary to popular belief.
I emailed the tech brewer involved in these trials, and here is the response :

"From my graphs it looks like hops needs 20-25 minutes for utilization. Means when you add it for Bitterness mid boil should be fine.
True, when you leave it boil for too long you loose bitterness again. That's because the bitter units ( in form of ISO alpha acids) bind to iron in the wort which binds to proteins and the whole complex comes out in the hot break. Also ISO alpha acids oxidize and you loose them that way.
From a wort clarification point of view it is always good to give a certain amount of hops at the start e.g. 50% and the rest in the middle of the boil. Utilization will be fine. If you want to do something for your flavor stability I would think about adding some hops at the end as well. You won't get more utilization but you have more un-isomerised alpha acids in solution and alpha acids form even stronger strong bonds with iron (compared to ISO alpha acids)- iron participates and flavor stability improves as less iron can catalyze the Fenton Haber Weiss reaction (oxidation reaction). Less iron also means less chill haze - you participate more proteins etc.
I wouldn't waste Aroma hops for bitterness. I'd always give it as late as possible. I prefer Whirlpool over end of boil. To keep as many aroma oils as possible"

[Frequent Sequence]

very interesting. can you describe the process involved with post fermentation bittering hops ? I guess you mean iomerised extract.
What is you take on other hopping techniques such as first wort hopping? every thing i have read has suggested that the bitterness is increased by about 10%.
This would seem to be contrairy to your info. although there may be some mechanism I am missing.

Cheers

[Qs]

FWH increases IBUs but can give a less harsh perceived bitterness.

[Frequent Sequence]

Yes that is what i have read also. However the info that Sorcerers Apprentice is giving seems to run contrary to that.

[Sorcerers Apprentice]

Hi lads sorry for the delay in getting back, I had problems with my phone.
The most significant advantage of first wort hopping for homebrewers I feel is from a safety prospective, the pre-boil hop additions reduce foaming and help minimise boil-overs. Some guys like to push their boil kettle volumes to the limit, and I prefer to add the hops earlier rather than resort to anti-foam additions.
Secondly the mid boil hop additions improved our hop utilisation, over the course of the trials it was discovered as per the email that 25 - 30 minutes were required to isomerise the hops, it was also found that after this time bittering units reduced again for the reasons outlined in the email. As I mentioned this is contrary to popular belief, but it is what our tests demonstrated and as a result we changed our hopping regime.
Getting back to the original question, some brewers were questioning whether to drop mid boil hop additions and just add hops at the beginning and end. Our findings were that mid boil additions had a function and actually improved bitterness levels.
There are so many variables regarding hop utilisation, ie age of hops, storage conditions, natural variations between batches, not to mention brewing equipment and boil vigour etc etc...
This is the reason we test each brew and blend as necessary.
I have also read on various internet sites that bitterness increases by 10% with FWH but I don't know have the people stating this actually tested this advice or is it an estimate/guess, which then gets quoted as gospel?
I am aware that professional brewing equipment will differ in performance to our smaller homebrew set ups, but the chemistry is the same.
If reducing the number of hop additions were being considered, I would question the number a late addition aroma hops ie the 15/10/5 minute additions and add these post boil with a lid on the kettle?
Anyway each to their own as the saying goes