Wednesday, June 13, 2007

IBUs + The Jamil Show

In the September 25, 2006 episode of The Jamil Show on Munich Helles, Mr. Malty himself makes a comment about hop utilization that really caught me off guard. If you listen to the show, you can find it at just around the 32:43 minute mark. For those of you who don't feel like downloading it, I'll transcribe it for you here:

"It boils down to the fact that really the difference in bittering from like a 30 minute addition to a 60 minute addition is almost neglible."

Really? I'm going to have to look into this. Here it goes!

I don't know what other people are using out there to get IBU estimates when putting together a recipe, but I'm a big fan of Tinseth's Utilization Formula. I will admit at the outset that I don't know whether or not Jamil's statement was supposed to be applicable to worts of drastically different original gravities or not. As they had been discussing the Munich Helles style, I'm going to use an original gravity that would be typical of that style to run some quick calculations. In this case, I'm going to use 1.050. Luckily for me, Tinseth's table on the page linked above includes the points where 1.050 and 30 minutes and 1.050 and 60 minutes intersect.

According to Tinseth, the utilization rate for a wort of 1.050 for 30 minute hop boil is 0.177. The utilization rate for a wort of 1.050 for 60 minute hop boil is 0.231. Let's say that I want to hop 5 gallons of a 1.050 OG wort with 1.5 ozs. of Hallertau at 5% alpha acid.

Tinseth proposes calculating IBUs in the following fashion:

IBUs = decimal alpha acid utilization * mg/L of added alpha acids

In order to determine mg/L of added alpha acids, we use the following:

mg/L of added alpha acids = (decimal AA rating * ozs hops * 7490) / (volume of finished beer in gallons )

.05 (decimal AA rating) * 1.5 (ozs hops) * 7490 = 561.75

Divide 561.75/5 = 112.3

.177 (decimal alpha acid utilization for 30 minutes) * 112.3 (mg/L of added alpha acids) = 19.87. We can round to 20 IBUs.

Now for 60 minutes:

.231 (decimal alpha acid utilization for 60 minutes) * 112.3 (mg/L of added alpha acids) = 24.94. We can round to 25 IBUs.

It tentatively appears as though he is correct. I believe Ray Daniels pointed out in Designing Great Beers that the human tongue typically cannot discern a difference of 10 IBUs. (I'll have to double-check on this one as I don't have the book in front of me, but I think this is close.) If that's the case, why do we boil our hops for 60 minutes for bittering rather than 30, or 45? Intuitively it seems that we would retain more of the volatile flavor compounds that would otherwise be lost in a longer boil.

I'm going to have to look around to see if I can either back up or refute this claim.


Anonymous said...

I know this is tremendously old, but I thought I'd ask if you'd done any follow-up on this? Maybe the difference between a 30-minute boil and a 60-minute boil isn't so much in the actual IBU contribution but in the "other" stuff that hops bring. A longer boil may not give too much more bitterness, but it may drive off flavors that would get in the way of the intended flavor.

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