Boil Volume and Hop Utilization

[d32h9]

Hey all,

So, I've been brewing for about 4 months now, and have made several fairly good beers. I've been using True Brew kits and adding extra ingredients to make them "my own."

I downloaded a brewing tool and decided to make my own beer not using a kit (still using extract.) When I added the hops that I wanted, I landed in the correct IBU range that I was looking for (about 20-25 IBU). I noticed, however, that I had a 6.5Gal boil size set. I brew on a stove top, and generally boil about 2-2.5Gal, then add it to 3Gal of cold water once I've cooled my boil. This being the case, I changed the "boil size" to 2.5Gal, and it cut my IBU in half!

I can understand that not boiling the whole batch would lead to fewer IBUs, however I'm wondering why the beers I have done taste so good/hoppy if they had an obviously low IBU value?

I've made an IPA that tasted very hoppy and bitter, as you would expect. When I entered it into my program, with a boil size of 6.5Gal, it hit about 48 IBU, which is what I would expect, because that is how it tasted. However, when I made it, I only boiled 2.5Gal, which my program tells me would drop my beer to like 23 IBU.

I'm having a hard time understanding why a "low IBU beer" based on a low boil volume would taste as hoppy as something I would expect from a 40+ IBU Beer? Any words of wisdom?

 

[Codemunki]

Boil volume (which affects boil gravity) does affect hop utilization to some degree, but not by over 50%. It's more like 10% at best. Some people swear it doesn't make any difference at all.

Without knowing what software you're using it is hard to know how it is doing the calculation. Your intuition is correct, though. The IBUs of your partial boils should be much closer to the IBUs of the full boil. My guess is that is user error of the software. Some more details would help to troubleshoot it.

 

[d32h9]

Thanks for the quick reply codemunki

The tool is iBrewMaster for the iPhone. It seems really legit, estimates OG and FG accurately bases on grain and extract inputs, so I assumed it calculates IBUs as well based on boil volume, boil time, and alpha acids based on specific hops, but maybe not.

 

[Codemunki]

Never used that tool, so I can't offer any specific help. Generally speaking, though, your IBUs for a full boil will be roughly 10-15% higher than a partial boil. Some partial boil extract recipes will have you add half of the extract with 15-20 minutes left in the boil to get better hop utilization.

If you have a PC, BeerSmith is a pretty comprehensive tool for calculating and scaling recipes based on lots of variables. It costs $21, but has a timed free trial, so you can see if it solves this particular problem. I don't know of any Mac software.

 

[TipsyDragon]

I've used that software. ignore the IBU calculations and report the problem to the person that made it. he is very good about fixing bugs like that. IBUs are based on boil gravity, final batch size, and the things you mentioned. what is probably happening is he is calculating the boil gravity based on ALL the fermentables listed being put into the boil size you listed. I've mentioned to him before that he should have a boil gravity listing on his recipes and use that in the IBU calculation. but so far he hasn't put it in.

 

[david_42]

Don't confuse hoppy and bitterness. A small boil volume changes IBUs, but has no impact on flavor/aroma.

 

[73Drvr]

Current CW is that hop utilization is NOT dependent on wort gravity. Rather IBUs are reduced with increased hot break in higher gravity beers. Since a large majority of hot break is already eliminated in the extract production process we extract brewers don't really have to take this in to account. I would hypothesize that this is why you are experiencing hoppier beers than your calculator would suggest. This, and it doesn't help that there are several different formulas for calculating IBUs and they come up with wildly different numbers. Along with the fact that the human palate can't detect small IBU variations.

John Palmer discussed this in a BBR episode a year or so ago. He said that his next edition of How to Brew will be updated to include this new info.