From the HBD Archive
From: darrylri@microsoft.com
Subject: re: IBU <-> HBU revisited...
Date: 1992-03-12 14:54:22 GMT

whg@sunfa.tellabs.com (Walter H. Gude) writes:
> Several sources give the %utilization number as 28% for leaf, 30% for pellet,
> given a 60 minute boil of "standard" gravity wort (1.040-1.045). Plugging
> it all in we get IBU=HBU(or AAU)*~4.5.

The numbers I've seen from Dr. Fix indicate more like 25% and 30%. Also,
George has indicated that pressure can have a dramatic effect on the
utilization.

> While persuing Micheal Jackson's New World Guild to Beer, he references
> 45 IBUs as extremely bitter. Now my beers with 10AAUs for 60 min. are
> not overly bitter. Why? Because like most partial mash brewers, I only
> boil about 2.5 gallons of wort. This means my boil has a gravity of about
> 1.090 for my "standard" beer. And my utilization is obviously far less
> than 30%.
>
> Does anyone have a formula for %utilization, incorperating gravity
> and boil time?

See the hops special issue of zymurgy, an article by Jackie Rager
on calculating hop bitterness. His formulae (which are sometimes
difficult to follow, sadly), includes a fudge factor for gravities
over 1.050. As I recall (and I am doing this from memory), for
each 10 points above 50 of gravity, Rager figures a 5% reduction
in utilization. I don't know what he bases this on.

> (I understand that this information may be buried in a Lotus 1-2-3
> spreadsheet authored by the infamous Mr. Richman.)

I'm not sure to what I can attribute my infamy (I hope it was
something really good, though), but my original spreadsheet
was written in Excel for the Mac. It had cells for pellet and whole
hop utilization right up at the top, out in the open. There was no
fudge factor for high gravities, and it is naturally inaccurate
because of that.

The Brewer's Worksheet, as I called it, has subsequently
been ported by others to 1-2-3 and Excel for the PC, and was available
on sumex-aim.stanford.edu and mthvax.cs.miami.edu for anonymous
ftp. (Has this changed? I haven't looked since I uploaded it.)

--Darryl Richman


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