Question about full boil vs. partial boil

[Yooper]

Well, there's where you get into a tricky area. I got interested in the subject because the hops corrections software was giving made everything too hoppy for my extract brews; personally I'd adjust a little bit (to account for the precipitation factor Palmer discusses in that podcast), but only maybe 10% more bittering hops and no adjustment on the 15 minute or less additions.

Unfortunately while the newer research shows that the old formulas are wrong, there isn't a well-accepted replacement yet; some people (including some really experienced brewers who know their stuff--e.g. YooperBrew) still think the old adjustments are fairly close, while others (including other experienced brewers who know their stuff, e.g. the measurements at BBR) would have you adjust very little or not at all.

Sumner and I have talked about this, and I'll further explain my own findings.

In a normally low IBU beer (15 IBUs), doing a full boil gave me an unexpectedly bitter beer. This was before I had Beersmith or heard that a full boil (or late extract addition) might change hops utilization. I remember saying, "This beer is twice as bitter as the last time I made it!" after my first full boil with it. Later, after I got Beersmith, I saw that the full boil changed the IBUs from 15 to 28. Which seemed about right to me, in the taste.

In a higher IBU beer, there was a much less noticeable effect. In an APA, I don't remember even noticing a difference! Possibly because there isn't an easy way to determine, say, 35 IBUs from 45 IBUs (as an example- I didn't calculate anything!).

So, when I discussed this with John Palmer (who originally said there was an impact of gravity on hops utilization), he blamed it on "break material" in the kettle. That is, the gravity doesn't affect hops utilization but instead the amount of break material does.

Also, when making hoppy beers, keep in mind that only so much of the hops oils can isomerize, and probably max out at 100 IBUs or so if you believe the current theories. That means if you're making a 75 IBU beer with a 2.5 gallon partial boil, well, you can't. Whatever IBUs you manage to get into the beer will be diluted by the top off water. So, if you do manage to get 3 gallons of 95 IBU wort, adding 3 gallons of top off water will definitely affect the bitterness. I'm not sure how accurate that is, but it makes sense that there IS a saturation point. If you do a full boil or a late addition of extract in this beer, you will have greater bitterness than a partial boil. And you'll be closer to the AG version of the same recipe, in that respect (boil volume, break material, gravity, etc).

All that to say this- for non-hoppy beers, where the bittering may be overpowering if you're making a beer like a cream ale, it won't hurt to reduce the bittering hops by 15% or so in a full boil or a late addition of the extract. But for a hoppy beer, particularly if it's a pretty high IBU beer, I wouldn't bother. Just be mindful of the ingredients and the desired effects.

 

[SquirrelMaster]

thanks for posting the basicbrewing podcast, makes me feel much better! i had actually listened to that before i started homebrewing but i guess it didn't really sink in until i listened to it again now.

the one slight concern i still have is, and they mention it for a second on the podcast, would the results be any different on a high IBU beer? They did their tests using an ipa of about 60 IBUs. when brewing a full boil, partial and partial late extract, the beers came out essentially the same. One of the guys mentioned the results could be slightly different if the intended beer was 100+ IBUs. While there might be some loss, i'm at least more certain now that it would not be the 50% loss that beersmith suggests when doing a partial boil

 

[SumnerH]

Also, when making hoppy beers, keep in mind that only so much of the hops oils can isomerize, and probably max out at 100 IBUs or so if you believe the current theories. That means if you're making a 75 IBU beer with a 2.5 gallon partial boil, well, you can't.

the one slight concern i still have is, and they mention it for a second on the podcast, would the results be any different on a high IBU beer? They did their tests using an ipa of about 60 IBUs. when brewing a full boil, partial and partial late extract, the beers came out essentially the same. One of the guys mentioned the results could be slightly different if the intended beer was 100+ IBUs. While there might be some loss, i'm at least more certain now that it would not be the 50% loss that beersmith suggests when doing a partial boil

The point they were making is exactly the one Yooper is talking about above. There's got to be some saturation point beyond which you simply can't get any more isomerized oils into solution.

The question is what that point is. Yooper's right that if it is, say, 100 IBUs then you couldn't do more than a 50 IBU beer in a 2.5 gallon partial boil. On the other hand in the BBR test they had no problem brewing a 60 IBU beer with a 2.5 gallon boil--that should mean the limit's at least 120 IBUs.

It could be exactly that, or it could be 150 or 500 or 10000 IBUs; AFAIK, there hasn't been any testing done on that front (BBR said they were planning a follow up, but if they've done it I missed it).

 

[SquirrelMaster]

i emailed basicbrewing, will let you know if hear back about any updates

 

[neomantra]

squirrelmaster, any news on this? it sounds like the methodology for calculating the various thresholds for partial and full boils should be straightforward for someone with the right equipment to measure real IBUs.