From the HBD Archive
From: (Chris Shenton)
Subject: IBU, AAU's, HBU
Date: 1992-03-04 19:43:09 GMT

On Mar 3, Walter H. Gude < > writes:

> Ay, the confusion. As I understand it:
> HBUs are # of oz. of hops times alpha acid.
> AAUs are (#oz. * AA) per gallon of wort. (or is it per 5 gal.)
> And IBU are probalby a linear multiplication of AAUs. (i.e. AAUs*Constant).

Yeah, it's a pain. AAUs and HBUs are the same thing, as far as I've
ever been able to tell: ounces X alpha. The problem with it is
that it ignores the quantity of beer (eg: 10 AAUs in 5 gallons will
taste different than 10 AAUs in 10 gallons). That's my biggest
complaint -- it doesn't describe bitterness in a batch-size
independent way. (In it's defense, it *is* like saying 10# grain -- in
5 gallons, or 10 gallons?)

I've switched to IBUs because I can compare with known beers
bitterness like those listed in Fred Eckerds wonderfully useful
(hype!) book, The Essentials of Beer Styles.

I still use AAUs or -- gasp -- ounces when I'm using the hops after
the boil, when their bitterness will *not* be extracted. IBUs are
meaningless there, because IBUs also depend on the hop utilization
based on boiling time.

Hope this helps more than it confuses.

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