[Haawa_Swede]

I read a comment on a forum about higher gravity mash reducing alfa acid utilisation (also stated in John Palmers book). That lead me to think about the opposite scenario; "What if the gravity is very low? What if I boil the bitter hops separately from the mash?"
I entered some values in the Beersmith software which gave the following result:
Standard boil: 20 l mash (6 kg pale ale malt and 40 g Zeus (16.6%)) gives OG 1,066 and IBU=68,4
Separate boil: 15 l mash with 6 kg malt gives OG=1,087.  5 litre water and 40 g hops gives IBU=334.
Mixed together we have 20 l mash with OG 1,066 and IBU=83.5. 
Ergo: 22% higher alfa acid utilisation.

I have tried to find any disadvantages but so far I have not found any.

I see some benefits though:
Reduced cost for bittering hops
Reduced wort volume
- quicker process - faster heating and cooling - which also improves the quality
- lower requirements for heating equipment
- smaller kettle can be used 
The "Hops water" can be cooled separately and used to chill the wort.

I don't see any reason for vigorous boil of the hops, maybe it can even be boiled with a lid on the kettle?
Can the aroma hops also be added to the Hops kettle? I don't see any reason why not. With a lid on the kettle and slow boiling the aroma possibly is maintained better.
I will try this next week, unless someone with more experience than me advices me not to.

So, has anyone tried? Do the hops need the malt (or the opposite) during the boil?
I use the BIAB method brewing American IPAs but I use a second water rinse to extract the last of the sugar. Could this part of the mash be used for hop boil since it has very low gravity?

[morticaixavier]

isomerization reaches a point of diminishing returns and drops off quickly around 100 IBU so the theoretical 334 IBU are not really possible to acheive.

There are interactions between the sugars, proteins, and other materials in the wort that affect the flavor of the final product. a hop tea mixed with a malt sweet liquid does not taste the same as hops boiled in the malt sweet liquid.

but give it a try and see what happens. if you do a one gallon batch you won't lose much if it's gross.

[Haawa_Swede]

Thanks morticaixavier! I did not know about the diminishing returns, too bad. It makes me wonder about a Beer that I saw that had a label stating 1000 IBU!
Yes, maybe it was too good to be true, but I will try a small batch (as you say) and report back. 

[morticaixavier]

Thanks morticaixavier! I did not know about the diminishing returns, too bad. It makes me wonder about a Beer that I saw that had a label stating 1000 IBU!
Yes, maybe it was too good to be true, but I will try a small batch (as you say) and report back.

I had that beer. Good is not a word I would use to describe it. That is a calculated value like your 334 IBU. they put enough hops in the beer to reach 1000IBU if that were possible. what they got was a nasty bitter liquid that tasted more like lawn clippings than beer and spoiled your palate for the rest of the evening.