If the BU:GU ratio is intended to give a sense of the perceived bitterness of a beer then why does it use OG as an input variable?
Most of the sugar of that OG is going to (hopefully) turn in to alcohol. Also, how much OG you start with may not directly correlate predictively to how much residual sugar is in the beer.
So, it confuses my why OG is used instead of FG?
Use the relative bitterness ratio: RBR = (BU:GU) x (1 + (ADF - 0.7655))
Don’t confuse your perception of bitterness with this ratio. They are 2 entirely different things. The ratio gives you a reference point that you can compare to your perception of bitterness in a particular beer or style. Whether you use OG or FG, you’d still be getting a reference point. The ratios would be quite different, but could still be used for the intended purpose. Suppose you like a particular Pale Ale and find a clone recipe for it. You brew the recipe and perceive it to be much more bitter than the original beer. If you decided to rebrew the beer, you’d use the ratio as a reference for determining how much you want to reduce the IBUs.
OG lines up much better with IBUs than FG does, with average ratios of most styles coming in between .25 and 1.25. It also makes more sense mathematically. OG is much more predictable than FG because less factors are involved. Because OG is a larger number, an error of a few gravity points means much less than the same error would if using FG. This, in turn, affects the ratio much less.
Just a couple of reasons I like using OG.
Hard as we might try, humans don’t have a really good handle on what a specific FG tastes like. Some sugars in the finished beer might be perceived as somewhat sweet, while many other remaining sugars in the beer, dextrins, are not really sweet at all but can provide body. If we used FG:BU ratio, results would be inconsistent because FG doesn’t necessarily taste like anything specific. I have had low FG beers that still have good body and do not taste overly dry, as often as I have tasted high FG beers that still drank like normal beers, full of malt flavor, but just had lower alcohol.
Meanwhile, we can certainly taste malt flavors and alcohol, as well as bitterness. Generally, higher OG comes from more malt, and a lower concentration of malt will give generally lower OG.
So in effect, I suppose the BU:GU ratio is really measuring not the balance of residual sugars and dextrins vs. bitterness, but rather the balance of malt FLAVORS vs. bitterness. Maybe think about it this way and it might make more sense.
Given how hoppy beers are in the 21st century, I wonder out loud for a moment whether it ever might make any sense to try to develop a similar measure for hop flavor balance, instead of just using IBUs which are generally bitter but may or may not have much hop flavor. But how would we possibly come up with such a unit of measure for relative hop flavor? There are probably 100 ways to get hop flavor in the beer so this would probably be impossible.
Bottom line: I see no value in knowing the FG:BU ratio. I can’t consistently taste an FG unit. I can, however, compare how malty a beer tastes against another, and this is different and more important than how much sugar or dextrins are left in the beer, at least to me.
One reason is that you won’t know for sure where a beer will end up until you brew it several times and find the range where FG normally falls with a recipe. By that time you don’t really need the BU:GU ratio because you already have the recipe built. BU:GU gives you an idea of what to target when you’re creating the recipe in the first place. Sure you could use software to predict FG but that’s not always correct.
For another reason, what would BU:FG tell you that would be helpful data? BU:GU gives you insight how the alcohol content will affect bitterness (because alcohol is impressionably sweet) and how much the overall heft of the beer affects the impression of bitterness. A 1.030 beer with 30 IBUs will be moderately bitter as will a 1.070 beer with 70 IBUs. Those are linearly fairly equivalent in bitterness. What could you glean from two 1.008 FG beers with 30 IBUs and 70 IBUs not knowing the OG? You might assume the 70 IBU beer is far more bitter but in practice they really wouldn’t be that far off. The difference between two 1.070 OG beers with 70 IBUs and FGs of 1.008 and 1.012 is not that much that it would be a helpful number in crafting the recipe.
I do agree, however, that FG matters in dialing in a recipe and BU:GU is not an absolute metric.
^^^^^ This
i believe ethanol is sweet?
Depends who you ask. I don’t think so.
Makes sense!