In recent times there has been a lot of talk about the "quality" of bitterness. The oldest bit of brewing lore to this effect is the claim that hop varieties that contain higher cohumulone give a harsher bitterness to the finished beer. The flip side is that other hop varieties may give a "softer", "smoother" or "neutral" bitterness. More recently, the proponents of first-wort hopping (FWH) claim that it provides a smoother bitterness than a traditional 60-minute addition. (Count me in this group, by the way) The same claim has been made regarding whirlpool or hop-stand additions (well, I know that I claim this at least).
Just to be clear, the claim here isn't that there is a difference in utilization or IBU's using these methods. The claim is that for a given number of IBU's, certain hopping schemes will provide a harsher or smoother bitterness. For example, a 60-minute boil addition of Chinook is (supposedly) going to give a harsher bitterness than something like a FWH of Liberty, even if they measure the exact same IBU's.
So this begs the question - what the hell does this mean, and how do you quantify it? Is 20 IBU's of Chinook at 60 min the same as 40 IBU's of Liberty as FWH? 30 IBU's? 50 IBU's? Or is it something else completely? Do we need one measure of IBU's and a separate measure of harshness?
Some brewers calculate the IBU's from a FWH addition as the equivalent of a 20-minute addition. Others calculate it as 70-80 minutes. The first way tries to account for the "smoothness/harshness" effect on the quality of bitterness, but doesn't factor in the additional utilization from the longer time the hops are in contact with hot wort. The second approach probably approximates the actual measured IBU's better, but doesn't factor in that this bittering may seem smoother. Is one way better than the other? I used to be firmly in the 20-minute addition camp. Now I'm on the fence and leaning towards the 70-80 minute camp, but with a caveat.
I have recently started to gravitate to the idea that IBUs and "Bittering Quality" are not only two completely separate descriptors, but also that they need to be considered separately. I think that attempts to approximate the affect on the smoothness or harshness of a hopping regimen by adjusting IBU's are missing a big part of the picture. Dialing in a hoppy brew really requires understanding what each addition is doing.
Let me share an example before I open the floor for discussion. Last year I brewed an IPA using nothing but flameout hops with a 90-minute hop stand, and some dry hops. I used an insane amount of hops (11 oz in my hop stand and 6 oz of dry hops for a 3-gallon batch). I sent the beer out for lab analysis, and it measured at 98 IBU's. But, to my palate, it tasted like about 60 IBU's, with a pretty smooth bitterness (similar to what I'd get from FWH). It tasted like an amped-up APA more than an enamel-stripping IPA. But the first time I drank it with food, something bizarre happened. I could instantly taste all 98 of those IBU's and my palate was completely blown out for dinner (which was a shame - it was a real nice ribeye). This really cemented the whole "IBU's vs harshness" idea for me. The beer somehow managed to hide its bitterness until I forced its hand with food.
So, what do we do about this dichotomy of bitterness? Damned if I knew. But now that my eyes are opened to this, I'll be paying close attention.