Are you still seeing "negligible" differences in IBU between a 2.5 gallon boil and a 5 gallon boil? I do not have enough experience to speak to that topic yet. I see you mentioned that the software has not caught up with your observation yet. Do you feel that the IBUs listed for a full boil are the more accurate readings? If that is true, then would it be better to calculate recipes for a 5 gallon boil, and not increase the hops-load to compensate for smaller boil volumes?
There have been recent talks/studies about IBUs, but I can point you to two that readily come to mind. Basic Brewing Radio has two podcasts- one is with John Palmer saying "What is an IBU, really?" The second I cannot remember the name of, but it's from about 2 years ago and there is an experiment with three brews. One was a full boil, one was a partial boil, and one was a late extract addition I believe. The IBUs were actually tested, and they were the same. I'm sure you could find it with a search, and give it a listen.
And it does go along with my experience. Sort of. In my experience, very low IBUs are a bit more bitter when done with a full boil. But then, with some age, they taste the same. I did this with my Dead Guy clone about 5(?) years ago. It's like a 15 IBU beer (off of the top of my head). Doing it as a full boil showed something like 27 IBUs. And it did seem to be much bitter when first sampled. But within about 6 weeks the beer was indistinguishable from the original.
John Palmer told me that any difference in IBUs may be related to the amount of break material in a smaller boil (the theory being that more break material would fall out, and the hops oils "cling" to it and fall out with it), but he wasn't sure. But he did tell me that IBUs are NOT dependent on wort gravity like he previously thought and stated in How To Brew.
>.Without exception, a full boil will make a better beer assuming you can chill 5 gallons of boiling wort. If you can do it, do it!
Yooper, I've seen you mention this a few times. Is this based on personal experience, or are there some articles you could point me to?
I still don't see why a full boil will taste better than a topped off smaller boil.
A smaller amount of water will absorb less hops oils/IBU (since the smaller amount of water is more saturated).
There are lots of articles and Basic Brewing podcasts that address this. I guess the best way to describe it is this. Which is better, fresh squeezed orange juice, or the condensed stuff you add water to?
That's overly simplistic, of course, but there are many things that happen during the boil. One of the big ones is Maillard reactions. With a thicker, higher gravity wort, the wort will turn darker and experience more Maillard reactions. That's like caramelization, and makes more of a "cooked extract" taste. Adding water to it doesn't later can't change the Maillard reactions that already occurred.
For a beer like an IPA, it's important to boil more if you can because of the IBUs. I know I said utilization doesn't change, and it doesn't. EXCEPT for this- there is a maximum amount of hops oils that can isomerize in wort before the wort is saturated. Most brewing science gurus put that number at 100 IBUs, give or take. That means if you're going a partial boil of an IPA, the most you can get in a 2.5 gallons is 100 IBUs. That's alot, so for a full boil it's not a big deal. But, if you have 2.5 gallons of IBU wort, and top it up with 2.5 gallons of water (0 IBUs), you end up with a max of 50 IBUs in your IPA (and it's probably less- more like 85 or so in the 2.5 gallon boil). That's why some partial boil brewers complain of too-sweet beers when they try to make barleywines or IPAs.
Adding the extract later in the boil helps when a brewer has to do a partial boil, as it decreases the maillard reactions that occur and keep the wort from browning and "cooking" so much. It also maximizes the IBUs to the greatest extent possible as there is less break material to pull out the IBUs. (If John Palmer is right about this theory, and I think he's explained it to me well enough that I believe he is right).
