Maybe I'm looking into this too much, but I'm a "units go with numbers and numbers go with units" kind of guy. I read "Designing Great Beers" by Ray Daniels (excellent book btw), and I love the BU:GU ratio concept, but I have one problem with it. Since IBUs are there own units, it's implied that if IBU=70 the beers has 70 Bitterness Units (BUs). My question is, are GUs the same or do they actually have units?
This all came about because we get the GU from the OG of the beer, for example OG=1.050 --> GU=50. But OG has units of kg/L. Did someone one day just decide to create GUs by taking the last 2 digits of the OG? Or is there a conversion step that I'm missing? If it is the former, it seems pretty far-fetched considering that we use GUs to calculate mash efficiency, and predict OGs (which have units).
I guess what I'm really asking is, what is the history of Gravity Units?
Thanks to anyone who can clear this up.