siobhan

Recipes 

In the beginners' area, responding to a post on Scottish Ale, Storunner13 mentioned that more water in the boil would result in more bitterness.

Just wondering - why? How does that work? I'd assumed that the amount of time in the boil would be most important (assuming identical ingredients between compared batches).

ajdelange

Recipes 

That's a new one on me. I suppose the reasoning is that more water implies more dilute wort and more dilute wort dissolves more isomerized bittering principal from the hops.

MachineShopBrewing

Recipes 

I think you are referring to the fact that a full wort boil will result in better hop utilization when compared to a thick partial boil. As AJ said, this will allow more isomerization of AA's.

winvarin

Recipes 

If you read Palmer's Learn to Brew, check out Chapter 5 on Hops. He discusses utilization. Basically, what he boils it down to is that the volume of wort and the gravity of the wort, along with the amount of time you boil the hops go into determining the utilization.

He uses a scale developed by Tinseth to give utilization of hops boiled in a wort of a certain gravity for a certain amount of time. The math he uses is fairly straightforward. You determine the AAU contribution of your hops by multiplying the weight of hops you use by the AA% for the particular variety.

Then you determine the gravity of the wort in your boil (he gives instructions for that as well).

Then you look up the utilization on the Tinseth chart by taking the gravity of your starting boil and comparing it on the chart to the amount of time you intend to boil the hops in that gravity.

Finally, you multiply the AAUs contributed, the utilization and a constant for metric/standard conversion (explanation in the chapter). Then divide it by your final volume (batch size) to get the number of IBUs contributed by each hop.

So the short answer is ajdelange's. You get more utilization (and therefore more IBUs) boiling your hops in a larger, more dilute volume of liquid because, as Palmer states it, "hop utilization decreases with increasing wort gravity".

winvarin

Recipes 

Pun not intended but I just caught it and had to laugh a little.

SpanishCastleAle

Recipes 

I've seen several people dispute that statement. Their reasoning was that utilization was decreased by break material in the wort and not by gravity. Since the amount of break material is sometimes (even often) correlated with gravity, it sometimes (even often) gives a good estimate.

__________________
Early brewers were primarily women, mostly because it was deemed a woman's job. Mesopotamian men, of some 3,800 years ago, were obviously complete assclowns and had yet to realize the pleasure of brewing beer.- Beer Advocate

winvarin

Recipes 

My experience has borne out, perhaps anecdotally, that the larger kettle volume does increase hop utilization ... or at least perceived bitterness. But I have no scientific evidence to back up what about the larger volume (gravity or amount of break) is contributing to the increased bitterness.

I can't argue it either way. I was merely quoting something from Palmer that seems to back the claim made by a lot of brewers that increasing the volume appears to increase the bitterness extracted from your hops.

Pilgarlic

Recipes 

Without a very credible case to the contrary, I think most brewers will continue to embrace the "settled" maxim that lower gravity boils increase isomerization.

Pilgarlic

Recipes 

Alright, alright. I found the credible cases.

MachineShopBrewing

Recipes 

That sounds right. Just look at some commercial brewery recipes scaled for their systems. Then linearly scale them to a 5 gallon batch and you will find it wouldn't be enough hops to provide the stated bitterness.