I see on some beer specs that an IBU and a AA value is given. For example one beer is specced at 80 IBU and also 75 AA. I understand that they are both a bitterness measurements, but that's about it. Can someone explain further please,
IBU is usually a refference to the bitterness of the beer, AA is usually a reference to the % of Alpha acids in the hops (that make beer bitter). They are usually both listed as if you use a hop with less AA% (different growing conditions will effect this even for the same type) you will need to use more to get the same IBUs.
Just a guess, but are you confusing 'AA' (Apparent Attenuation - yeast property) for 'AAU' (Alpha Acid Units - hop property)?
Could be it, but it seems like an annoying way when they could have just listed ABV. How many people know how to calculated the ABV when given the starting gravity (in Plato) and the attenuation? Maybe they are just giving the beer geeks something to feel superior over
The AA% of a hop and the amount you use (and when you use it) give you your IBUs. A simply way to see the connection is to use Homebrewers Bitterness Units (HBU...I know, another abbreviation)
HBU is simply the AA% of a hop x the ounce amount you use. So when you use 1 ounce of a 10% hop, you get an HBU of 10. If you used 1/2 ounce of a 20% hop you would also get an HBU of 10...basically the same bitterness.
I would consider using a program to get your IBUs like beersmith.