Sunday, April 3, 2011

BU:GU Ratios

If you're like me you didn't do all the research needed to understand all factors of brewing before you started brewing your first beers. I understood that the sweetness of malted barley in my beer needed to be offset by the bitterness of hops (for most beers) but I was relying on the recipe or the kit to take care of that little detail. Next, I started out looking at recipes that were 'clones' of beers I liked, and then sort of drifted into looking at the ingredients and thinking "Yeah, that would be tasty!" Eventually, I stared building my own recipes, stared looking at more of the math, started caring more about yeast pitch rates, water chemistry and all the other little details that go in to making a great beer. But the BU:GU ratio wasn't on my radar until recently. I'm now trying to figure out how the BU:GU Ratio can help me. Several of the brewing software programs calculate BU:GU values, but I haven't seen one that relates the number to anything meaningful.

The BU:GU Ratio is determined by dividing the number of IBUs in a beer by the number of points of original gravity to provide a rough estimate of the balance between hop bitterness compared to the malt sweetness. The idea originated in Ray Daniel’s book 'Designing Great Beers'. According to the book it is...
"The ratio of bitterness units to gravity units for a specific beer or group of beers. International bitterness units (IBU) are used for for bitterness and gravity units (GU) are used for the gravity component."[1]

To calculate, take the part of the OG after the decimal, and divide it into the IBUs. 0.5 is balanced, values under that are more malty, values above are hoppier. If you have a beer with 1.050 OG and 25 IBU, you're BU:GU balanced assuming that your IBU calculations are correct, which is a guess that Tinseth, Rager, Garetz and Daniels can't seem to agree on.

Chart of BU:GU Ratios The yellow section in the middle is balanced, gold and orange are progressively more malty, light and dark green are progressively more hoppy. It wouldn't be hard to create an IPA that is 'off the chart' but we're concentrating on the midpoint here.

The BU:GU Ratio is an attempt to quantify how balanced a beer is, but dark malts, estery yeasts, spices and sourness will throw off the perceived balance, and you can't factor all that into an equation. And what about different levels of attenuation? Maltodextrin will throw off the sweetness compared to measured gravity. Some styles will always be out of balance according to the basic BU:GU calculation. Does that make them bad? The BU:GU idea has some merit, but looking at the taste and bitterness of different beers, I'm thinking "Ray, what are you talking about, man?"

Not surprisingly, the average BU:GU ratios vary widely by style, so Daniels lists the average BU:GU ratio for some popular styles. Now things finally come together. Rather than looking at an 'absolute' measure of balance, we can look at the relative BU:GU ratio for the style.
"For most beers and beer styles, the resulting ratio has a value between 0.3 and 1.0."[2]
So now (drumroll) I can dial in the relative sweetness to style, whether I'm on the high side or the low side of the gravity for that style. Or I can do the same thing for a specific recipe. I could scale it up to an 'imperial' version and keep the relative BU:GU balance in line. For a given style, all I need now is a chart of those reference numbers. Designing Great Beers gives me a few numbers from NHC Second Round entries for starters, you're on your own for the rest of them.

StyleBU:GU Average
Dusseldorf Alt0.70
Barley Wine0.53-1.83
Ordinary Bitter1.28
Special Bitter0.58-1.07
Pale Ale0.58-1.12
English IPA0.61-1.64
English Brown0.50-0.70
American Brown0.95
Old Ale0.45-0.70
Bohemian Pilsner0.75-0.85
German Pilsner0.68-0.80
Munich Helles0.38-0.48
Brown Porter0.55-0.72
Robust Porter0.61-0.93
Scottish 60/Light0.30-0.55
Scottish 70/Heavy0.30-0.50
Scottish 80/Export0.30-0.50
Scottish 90/Strong0.35-0.40
Classic Stout0.80-1.20
Foreign Stout0.90
Sweet Stout0.30-0.50
Imperial Stout0.90
Berliner Weisse0.14-0.18
Dunkel Weizen0.21-0.29
Wiezen Bock0.20-0.23
American Wheat0.16-0.34

[1] Ray Daniels, Designing Great Beers
[2] Ray Daniels, Designing Great Beers

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