Tinseth IBU Calculations

[ayoungrad]

I am relatively new to brewing (4 batches so far) and I've been attempting to learn more about the process by creating my own excel spreadsheet for creating recipes. I have done a lot of work on it and I just finished the exhausting chore of calculating estimated IBUs by the various, somewhat accepted, authors. I then checked my calculations against online calculators.

After having done this I have a question that I was hoping could be answered here:

It seems as though several online calculators use OG for the Wort Gravity in Tinseth's Bigness Factor. But, reading (what I think) was posted by Tinseth himself on http://www.realbeer.com/hops/research.html he states "use an average gravity value for the entire boil to account for changes in the wort volume". Is using an average value of the boil gravity someone's interpretation of his work or is this his recommendation? If it is his recommendation, then are the online calculators wrong by using OG?

Thanks in advance.

 

[Brewsmith]

That page you linked to looks like it is Glenn Tinseth himself.

Calculating IBU's is not an exact science because there are a number of factors that go into the actual calculation, and some of the factors are based on a "best guess" such as the AA% of the hops that you are using. I wouldn't say any calculations or online calculators are wrong. Each are slightly different and end up with different results. The general rule is to use one consistently and use your palate to track how the numbers are perceived.

A great podcast interview with Tinseth himself is the 12-14-09 episode of Brew Strong on the Brewing Network

http://thebrewingnetwork.com/shows/588

 

[Brewsmith]

I think what he means by using an average is that if your beer has a preboil gravity of 1.045 and a post boil gravity of 1.055, just use an average of 1.050 as the gravity in the equation. Hop utilization changes with respect to wort gravity, and the gravity changes according to your boil off rate. Using the average just simplifies everything, especially with some of the assumptions that are made with the calculation.

 

[rocketman768]

I have spoken with Tinseth, and he himself recommends using the average boil gravity.

 

[ayoungrad]

That definitely answers my question. Thanks Guys.