Is it necessary to adjust the IBU’s on my recipe if I undershoot the OG or fermenter volume?
As best I can tell the IBU calculation in independent of OG but not volume.
If my original recipe gave me the following…
Batch size: 5.5 gallons
Target OG: 1.063
IBU’s: 49.9
But I ended up at…
Batch size: 5 gallons
Target OG: 1.052
IBU’s: ?
How would you propose to adjust it? I think you don’t worry about it and enjoy the beer.
You could use iso extract to adjust it, but I’m with Joe…just drink it, figure out what happened, and adjust for it next time.
But if he has less volume at a lower OG is he not more bitter already?
I suppose you could boil some DME and add the right volume/amount to bring the OG and volume back up, but that seems like a PITA.
Sorry…I should have worded this better. I am not looking to adjust the IBU’s to get to a certain point. I just want to know what the actual IBU’s are now with the changed volume/OG.
I am happy with what it is but I am guessing with coming up short with my OG and volume they are not 49.9 like my program calculated. Just want to know what the new number would be.
Lower gravity will give you higher hop utilization, plus smaller volume will give you more IBUs per unit volume. So, your IBUs will probably be more like upper 50s. This is going to taste like a very bitter beer indeed. But you might enjoy it that way anyway. And if not, bottle it and let it age for 6 or 9 months. Bitterness does drop out over time.
you can adjust the efficiency to hit the gravity you have and it will adjust the IBU in your brewing software.
for what it’s worth, it wouldn’t have actually been 49.9 even if you have hit your numbers exactly. There are too many system assumptions for even complex calculations to be really accurate.
True, but having a calculated IBU reference point to go with your perception of the beers you make is really helpful when making adjustments to recipes or formulating them.
That was my thought as well.
Does anybody really know what time it is? Does anybody really care? 
+2 to it being a reference point, totally accurate or not.
Opinion: Calculated IBUs is only helpful to the brewer. If you use the same hops, same IBU formula, then you have a tool for adjusting future batches. But for describing how bitter a specific beer actually is… I think we’d be better off just assigning a number that it seems to taste like. Maybe for example the computer says its 45 IBU, but if it tastes like 30, describe it as 30.
Numbers may tell you that your bitterness will be higher, but in all reality will you be able to really taste the difference? Perhaps. Or perhaps not. You will never know unless you brew the original recipe as intended.
Nice “Chicago” reference.
http://www.bayspec.com/spectroscopy/portable-mass-spectrometer/
just putting this out there as an option :
Using this calculator
http://realbeer.com/hops/bcalc_js.html
I made a hop addition to match your numbers: 1.9 oz 10% AA added at 60 min.
For the original recipe (1063 OG 5.5G) the calculator predicts 50 IBU (you stated 49.9).
I then changed the OG to 1052 and batch size to 5G with the same hop addition. The new predicted bitterness is 61 IBU.
So, according to this Tinseth calculator your bitterness will have increase by 20%. 20% sounds like a lot but I think your beer should be fine.
Two things you can do if the beer is too bitter:
I think is more along the lines of what you’re looking for:
$5,310 for the spectrophotometer is fine, but they want almost $100 for shipping. That’s where I draw the line.
Prime and MoreBeer ruined me too. I’ll spend an extra $20 with MoreBeer before I’ll give them $6 for shipping.
