That hasn’t been my experience, Jim. Every beer I’ve sent to be tested was within 1-2 IBU of the estimate from Promash using Tinseth calcs.
None of the calculators take into account the iso-AA saturation, so anything they predict over 70 or so is too, high, let alone higher than that.
Totally agree. Its when you are told your experience is wrong because a study says so that the rub exists. On this one, study stuff for a jump off point, then run with what your experience dictates.
Hmm, well there ya go. Usually folks report them being off. I guess it can also be acurate sometimes
Yep. The beers I’ve had analyzed were in the 35-60 range.
My Double IPA came out to 65. Tinseth had it around 90-100 IIRC.
Mine measured 98. Tinseth had 475 and Rager had 440. So Rager was quite a bit closer. Maybe you were using the wrong equation ;D
No, Tinsethth was very close on the other two that were measured. 
I did not realize that the publication was not open to the public until I logged into the forum from home. I wonder if the ACS would mind if I posted the table data to the forum with a reference to the source publication?
I have access to all the ACS journals at work. If someone really wants the article, shoot me a message. I’ve done enough work for ACS and their journals over the years - a relatively old article sent to a few people isn’t hurting their bottom line.
I have seen some data that shows isomoization at 70C (158F), though it is not much.
One thing that a 60 minute boil will give you is more cis than trans (68%cis vs 32% trans, or a 47% ratio). Longer boils of the majority of the IBUs will give a more lasting bitterness. The trans has a 1 year half life, cis has a 5 year half life. A beer that you want to age, like a barleywine would benefit from a good bittering charge at 60 to 90 minutes. Eventually the bitterness decreases to a balanced beer, then after that you get a malty beer. If you have done a 10 year Bigfoot vertical you know how that progresses.
Another paper with some good facts.
I wonder what these numbers would be for FWH. Also, I wonder about the difference in trans/cis ratio with FWH vs 60 min boil.
I am discovering that I have access to a lot of journals at work that I take for granted.
Question for someone with access to the full text: Is the 100°C sample the only one that was boiling? I certainly get more than 17% utilization out of a 90 min boil at 91°C.
From the experimental section of the above referenced article:
An all-glass round-bottom flask (500 mL) with 3 necks was used in two separate laboratory scale boiling experiments (250 mL scale). The first neck was used for online measurement of the temperature, the second neck was fitted to a reflux condenser to prevent evaporation, and the third opening was closed with a rubber septum for sampling as a function of time using a syringe. Boiling experiments were performed in aqueous buffer solution (0.1 M), prepared with 3,3-dimethylglutaric acid and NaOH (sodium hydroxide) to maintain a wort representative pH of 5.20. The flask containing buffer solution (250 mL) was heated in a laboratory stirrer/hot basket and continuously homogenized during the experiment with a magnetic stir bar. When the buffer achieved the required temperature (80, 90, or 100 °C), 2 mL of an ethanolic solution of commercial nonisomerized hop extract (International Calibration Extract ICE 2 containing 49.39% R-acids (w/w) and 24.94% -acids (w/w); Labor Veritas, Zu ̈rich, Switzerland) was added.
Initial R-acids levels were 60 mg/L. At selected time intervals (5, 10, 15, 20, 30, 45, 60, and 90 min), heated samples (5 mL) were taken using a syringe and cooled immediately in liquid nitrogen (-196 °C). Frozen samples were kept at -24 °C until further extraction and HPLC analysis.
You must be brewing somewhere higher than 10,000 ft elevation??
Just over. About 10,150 ft at my house.