When I first started exploring craft beers, I played it pretty safe. I stuck with malty, low to medium alcohol beers, such as hefs and brown ales. I started to journey into pale ale territory when I discovered Sierra Nevada’s Pale Ale. The hop bouquet andbitterness smacked me in the face and opened my eyes to beers that were *meant* to be bitter. The listed 38IBU of SN Pale Ale seemed pretty large to the 20IBU and lower beers I had been drinking. I thought that was pretty cool. It was something to brag to your macrolager buddies about. I was a man. Then, I discovered IPAs… and Double IPAs… and Imperial IPAs.

As the IBUs climbed, I noticed that the beers didn’t seem to be getting that much more bitter as I had expected. This culminated with the biggest beer I’ve ever had, Dogfish Head’s 120 Minute IPA. Weighing in at 120IBUs and packing an 18% ABV punch, I was expecting to be floored on my first drink. Surprisingly, it was more sweet than bitter to me. I wondered if my bitternessperceptions had changed that much or if something else was going on.

My perceptions had changed, but that was not what made the 120 seem sweet to me. After some deep thinking, I found the answer was obvious – balance. I noticed that beers with higher IBUs also had a higher ABV% (usually). ABV%, in a roundabout manner, measures the amount of sugar in a beer. You can find the ABV% of a beer if you know the OG and FG, and as we brewers know, OG and FG are measurements of the starting and finishing amounts of sugar, respectively. And sugar, in whatever form, balances out bitterness in a beer. Flying Dog even prints a neat little gauge on their beers with one end of the spectrum being bitter and the other end being sweet, so as to give prospective buyers a heads-up on what to expect.

So it makes sense that higher a IBU will coincide with a higher ABV%. I imagine a 150IBU, 5% ABV beer would taste very good. It certainly wouldn’t taste very balanced. Conversely, neither would a 5IBU, 15% ABV beer.

This brings us to the heart of the matter: bitterness ratio. The bitterness ratio can be thought of as a measure of perceivedbitterness. In its simplest form, the equation is: bitterness ratio = IBU / ((OG-1)*1000). For example, a beer with 30IBU and an OG of 1.060 would be: 30 / 60 = 0.5. (note: the equation above is a little messy, so an easier way of doing this is just to ignore everything to the left of the decimal and treat everything else as a whole number).

That’s the equation I see most often. I don’t think that’s the most accurate, however. Two beers with IBUs of 30 and OGs of 1.060, but finishing gravities of 1.020 and 1.001 will taste very different in terms of bitterness. The 1.020 FG will seem pretty sweet because of all that residual sugar, balancing out some of that bitterness, while the 1.001 will be very dry and enhance the perception of bitterness. Which is why I like to add the FG to the OG in the equation above. This becomes: bitterness ratio = IBU / ((OG+FG-2)*1000). In our previous example then, the first beer has a  BR=0.37 while the second beer is BR=0.49.

The BR number is meaningless if not put into context. Here are the BRs of some commercial beers (calculated from clone recipes in most cases):

Red Hook ESB =  0.53

Sam Adams Boston Lager = 0.56

Dos Equis = 0.35

Theakston’s Old Peculiar = 0.39

Bud Light = 0.24

Running Dogfish Head 120 Minute IPA through the equation yields a BR of 0.48. Sierra Nevada Pale Ale on the other hand has a BR of 0.57, making it the more bitter beer.

I like to think that a BR of 0.5 is right in the middle of the spectrum of bitter and sweet. This isn’t always appropriate for the style or situation, but it is certainly something to be aware of.

So there you have it – and explanation as to why some high IBU beers don’t seem as bitter as their low IBU bretheren.