« on: September 29, 2011, 06:25:10 AM »
The saturation limit for alpha acids in wort or water is on the order of 85 ppm and the conversion to iso-alpha acid approachs 90 percent of the alpha acids with an extended boil. An IBU is equal to 1 ppm iso-alpha acid. So, the maximum IBUs achievable in beer will never approach the exaggerated claims from some brewers. IBU models such as Rager and Tinseth don't take into account the saturation limit and they will show increasing IBUs with increasing hop and alpha acid addition.
That premise that the IBUs can exceed about 90 ppm is not factual and has been entirely proven by brewers that take the time to measure the amount of iso-alpha in their beers via lab methods. I heard Vinny Cilurzo quote that Pliny has only about 80 ppm on the best of conditions and more typically is around 75 ppm. That is more than enough evidence that the saturation limits I mention above are true and factual in practice.
Now that saturation limit for alpha acids and iso alpha acids doesn't mean that a brewer and drinker cannot achieve and percieve greater bittering through higher hop additions. There are other bittering and flavor compounds beside iso-alpha acids (oxidized beta acids are one). But their bittering effect and perception are far less than iso-alphas. I think its safe to say that a brewer can't really bitter a beer too far given this limitation for iso-alpha.
The standard for measuring bitterness is Quinine. I'd say that it may be possible to add more bittering to beer via an addition of that compound, but I'm not sure if its useful in beer. I'm betting that its been tried by someone before, but I haven't heard of it.
As a testament to the limitation of bittering in beers, take the case of Double IPAs. They are typically more balanced than IPAs even though the bittering levels calculated for those brews are typically astronomic. The level of malt overwhelms the bittering and lends to a more balanced perception. A true testament to that is that my wife will drink most Double IPAs, but finds most IPAs too bittered for her tastes.
A new IBU formula is needed that includes the limitation of iso-alpha saturation.