aekdbbop

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Why do you need to lower the amount of hops you use it you do a full boil? Seems like to me it would be the other way around...

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the_bird

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Lower gravity allows higher hops utilization - basically, the less "stuff" in the boiling wort, the easier it is for the hops oils to be extracted. I'm sure there's a more technical explanation, I'll leave that for someone who knows what they are talking about, but that works for me.

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zoebisch01

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Yeah, that's what Palmer talks about. Less 'room' for stuff the acids to become utilized. Although it is most likely way more complicated than that because if that were all of the story then adding additional hops wouldn't necessarily do any good. In other words if you have two feet of space to stand in and someone is already standing there and there is no more room where can they stand? The same thing, if there is only one space for a hop acid, and it is occupied then adding more hops wouldn't seem to make sense, and yet it does work but you the aa utilization just doesn't reach its potential. I am sure there is much more to the story, but I haven't found out yet.

I guess though it is probably a diminishing returns type of thing. I really wonder what the curves look like for utilization in say a 7 gal boil using 1, 2, 3, 4, 5 oz of hops. I haven't read anything good yet on how the acids actually seperate from the hops. Is it Kinetics? Temperature? It would be interesting to know.

RoaringBrewer

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These guys hit the basics (and as far as I understand) on the head...

There is some scientific reason (I think the 'less stuff in wort boil' analogy works fine for answering your question though) that the utilization of the hops alpha acids decreases in higher gravity wort boils; hence the need for more hops. I believe Papazian discusses this in both of his books (Complete Joy and Homebrewers Companion) in some depth (2+ pages) and also has charts showing the % utilization you can expect and IBU calcs you can make with this info.

Basically, I use Beersmith to assist me in hop utilization/IBU sort of things. You can change the boil-size within the program and it will automatically recalculate the IBUs, etc. from hops in your recipe. It is definitely true though that you need more hops to achieve the same bittering quality for more concentrated boils.

For example, I just plugged this into BeerSmith today (simplified a bit)
7lb. extract
About 1lb. Steeping grains
.5 oz. Chinook 12.4%AA for 60 mins
.75 oz. Chinook 12.4%AA for 30 mins
1 oz. Williamette 5.6%AA for 10 mins
Perle Dry Hop (no effect on IBU)

If I do a 5 gallon boil of this exact recipe, Beersmith outputs an estimated IBU of 51.4IBU. However, if I do a partial 2.5 gallon boil Beersmith estimates IBUs at only 32IBU. Quite a difference!! The utilization of the hops AAs is much less when the gravity of the wort boiled is doubled (5 gallon water with that extract/grain would be 1.052OG, but 2.5 gallon with the same ingredients would carry an OG of 1.105)...

Note that you can combat this problem somewhat by doing late extract additions. I.e. Boil hops for 30 mins with NO/little extract in the water, then add the extract for the last 30 mins. However, the problem with this is that none of the brewing software I've seen or books I've read have calculations to compensate for late additions. They always assume some sort of gravity to the wort being boiled with the hops (water would have "no" gravity at 1.0000).

RoaringBrewer

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Some of these may help? I didn't read them just did a yahoo search and linked:

http://realbeer.com/hops/research.html
this one at least has a good detailed chart of the utilizations for hops between 0-20AA, boil times of 3 min - 2 hours, and OGs of 1.010 - 1.150 or something like that...

http://www.beer-brewing.com/apex/hops/hop_utilization.htm
this looks like an entire brewers handbook with a whole chapter on the topic?

david_42

Recipes 

Take a glass of iced tea. Add a teaspoon of sugar, stir until dissolved while timing it. Repeat until no more sugar dissolves. Each addition takes longer to dissolve.

Do it again using carb drops.

With hops there are two main factors: the size of the resin grains, which controls the speed of isomerization, and the 'competition' from other dissolved solids. Hop utilization is one of the main sciences of brewing.

Isomerization kinetics Just an abstract, but it states 90 ppm (AKA IBU) is the limit. It's cool living & brewing in Oregon!

If you want to calculate bittering with late extract additions, just re-run your software with reduced or no extract. I know BYO's software gives valid results at 0 extract.

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