Post
by Graham » Thu Sep 01, 2011 3:36 am
I suppose that you should set the formula to Tinseth, because that is what many other people use. Hitting the Tinseth button will set base utilisation to 39.75%. The 39.75% base utilisation may seem high, but it is never achieved in practice. It is the hypothetical utilisation at zero original gravity and an infinite boil time. It is there to ensure that the formula matches the Tinseth numbers, and it is displayed in defaults so that it can be tweaked, should anybody want to. The other parts of the formula reduce that 39.75% considerably.
However, as crookedeyeboy's results illustrate (link in the above post), the Tinseth formula is pretty hopeless at predicting utilisation. For it have 53 EBUS error in a 48 EBU beer is not very impressive. The error is greater than the real bitterness. Indeed, in crookedeyeboy's recipe, if we take just the 90 minute bittering hops and ignore the later hops, the utilisation is just 16%. If the bitterness contribution from the later hops is factored in (which is not possible to calculate) the true utilisation would be even lower.
As a coincidence, there was a podcast on Basic Brewing Radio on August 11th that attempted to find an EBU ceiling, and strangely, after me doing a few sums, it turns out that they had similarly low utilisations, 16% @ 43.5 EBUs ; 12% @ 49.5 EBUs and just 9.3% @ 51.8 EBUs.
These utilisations are very much lower than we have been led to expect, and off the Tinseth scale. It makes the fixed utilisation of just 20% that I used in my early books seem more reasonable after all.
Although there were only 4 data points in the Basic Brewing experiment, it shows a definite alpha-acid saturation curve that seems to flatten out at about 50 EBU. This means that anything much greater than about 60 EBU is unachievable, and even then at ridiculously low utilisations, bearing in mind that BBR got just 9.3% util at 51.8 EBU. The acclaimed 100 EBU beers would be impossible if such a low saturation level was normal.
I am hoping that these poor results are something to do with wort boil pH being unacceptably low, but if that is not the case, home brewing has some serious rethinking to do. Even if this is associated with boil pH, there must still be loads of home brewers that are achieving nothing like the expected utilisation, because no-one has ever told anybody to measure and adjust boil pH.
Worrying stuff really.
