G
GottBeer
My question pertains to the on-going discussions of IBU calculations. I am fairly new to brewing and have been reading much about the various ways to estimate IBUs using the Rager, Tinseth, etc. equations. It seems that many believe that Tinseth is more "accurate," but I've also see opinions that Tinseth is better for full boils while Rager is better for partial boils. Using BeerSmith does it really matter whether you are doing a partial or full boil? I ask because for Tinseth it appears from playing around with the program that BeerSmith calculates the hops utilization (not final IBU) based on the boil volume, not the final beer volume, and then simply ratios the IBUs calculated from the boil by the final dilution. This would make sense to me since IBU is a measure of "bitterness concentration," but I want to confirm this is the case.
I can illustrate what I'm trying to ask with an example (making up the numbers). Say I want to boil 3 gallons with a final beer volume of 5 gallons. From what I can tell BeerSmith first calculates the IBUs assuming that the 3 gallon boil is a full boil and performs all of the utilization calculations assuming a 3 gallon boil. For my example the result would be 40 IBUs for this intermediate step. It then dilutes the beer, which is not related to extraction or utilization, to account for the final volume and concentration. In this case (ignoring losses to keep it simple) Final IBU = 40*3/5 = 24. I want to make sure that this is what BeerSmith is doing. If this is the case, then it shouldn't make any difference whether you are doing a full or partial boil. While it is true that the Tinseth equations assume a full boil, this can be compensated for by accounting for the dilution after the boil separately as it appear BeerSmith does. A bit of a ramble but I hope I'm being clear and that you can confirm my reasoning.
For my immediate problem I'm simply trying to scale an existing recipe to go from a full boil to a partial boil due to equipment limitations (my boil pot isn't big enough). I presume the goal here would be to keep the calculated IBUs constant between the full and partial boils regardless which method I use (i.e., if BeerSmith tells me the IBUs are 77.5 for the full boil, then I still want 77.5 IBUs with the partial boil, which would be expected to use more hops for the partial). I've done this assuming both Tinseth and Rager and am surprised that I am coming up with a quite different hop requirement depending on which method I pick (33 gm with the Tinseth vs. 38 gm with Rager). My inclination is to go with Tinseth, but . . .
Thanks for any opinions.
Dave
I can illustrate what I'm trying to ask with an example (making up the numbers). Say I want to boil 3 gallons with a final beer volume of 5 gallons. From what I can tell BeerSmith first calculates the IBUs assuming that the 3 gallon boil is a full boil and performs all of the utilization calculations assuming a 3 gallon boil. For my example the result would be 40 IBUs for this intermediate step. It then dilutes the beer, which is not related to extraction or utilization, to account for the final volume and concentration. In this case (ignoring losses to keep it simple) Final IBU = 40*3/5 = 24. I want to make sure that this is what BeerSmith is doing. If this is the case, then it shouldn't make any difference whether you are doing a full or partial boil. While it is true that the Tinseth equations assume a full boil, this can be compensated for by accounting for the dilution after the boil separately as it appear BeerSmith does. A bit of a ramble but I hope I'm being clear and that you can confirm my reasoning.
For my immediate problem I'm simply trying to scale an existing recipe to go from a full boil to a partial boil due to equipment limitations (my boil pot isn't big enough). I presume the goal here would be to keep the calculated IBUs constant between the full and partial boils regardless which method I use (i.e., if BeerSmith tells me the IBUs are 77.5 for the full boil, then I still want 77.5 IBUs with the partial boil, which would be expected to use more hops for the partial). I've done this assuming both Tinseth and Rager and am surprised that I am coming up with a quite different hop requirement depending on which method I pick (33 gm with the Tinseth vs. 38 gm with Rager). My inclination is to go with Tinseth, but . . .
Thanks for any opinions.
Dave