Relative Bitterness Ratio (RBR)
I have a new calculation that I’ve been using when determining the expected balance of my beer recipes. It is a child of the commonly-used Bitterness Ratio (BU:GU), and the numbers output can be read in the same way as BU:GU. However, the one thing that is taken into account with the Relative Bitterness Ratio (RBR) that BU:GU does not account for is Apparent Attenuation (ADF).
The higher the degree of Apparent Attenuation (ADF), the more fermentable sugars are consumed and the less residual sweetness is left behind. That means that as ADF gets higher, beer balance tends more toward the bitter end of the scale. As ADF gets lower, beer balance tends more toward the sweet end of the scale.
For example: A beer that starts out at an OG of 1.050 at 25 IBU would be said to have a Bitterness Ratio of 0.5. If it were split into two batches and one had an apparent attenuation of 80% (Beer A), while another had an apparent attenuation of 60% (Beer B), Beer A would be perceived to be more bitter than Beer B, as the latter has considerably more residual sweetness.
In the pages linked below, you can find out a plethora of information explaining details about the Relative Bitterness Ratio (RBR). If you aren’t interested in the details, I’ve included the formula for figuring out RBR as well as a simple calculator if you just want to input some numbers and get results.
To quickly explain the formula:
RBR = Relative Bitterness Ratio. ADF = Apparent Attenuation. 0.7655 is the average ADF of all beer styles. Since the Relative Bitterness Ratio takes into account balance relative to all beer styles, it uses this as a constant. You are comparing your beer’s ADF against the average ADF (0.7655), then adjusting the standard Bitterness Ratio accordingly (it goes up if your ADF is higher than average, down if your ADF is lower than average). Just like BU:GU, higher numbers mean more bitter, lower numbers mean less bitter, and 0.5 is roughly average balance.
RBR = (BU:GU) x (1 + (ADF - 0.7655))
- Relative Bitterness Ratio (RBR): A fairly detailed explanation of Relative Bitterness Ratio.
- Beer Style Data: The underlying data used for these charts plus all other style data from the 2008 BJCP Style Guidelines.
- Bitterness Ratios (Chart): The average bitterness ratio for every beer style with relevant data.
- Relative Bitterness Ratios (Chart): The average Relative Bittneress Ratio for every beer style with relevant data, corrected for attenutation.
- Balance Rank: The balance of beers relative to each other, with BU:GU lined up next to RBR.
- Relative Bitterness Calculator: A simple web-based calculator to calculate RBR using BU:GU and Apparent Attenuation.
- Beer Style Data (Google Docs): This is a link to all of this data over at Google Docs
- Mad Alchemist: The author’s (Ryan Shwayder) homebrew website.
- External Resources:
- 2008 BJCP Style Guidelines: The official 2008 BJCP Style Guidelines can all be found here. This is where the numbers came from.
- Balancing Your Beer with the Bitterness Ratio: This is from Brad Smith at BeerSmith. It explains how to get the BU:GU ratio in the first place.
- BeerSmith: My favorite brewing software. Free trial, but you have to pay for the full version. It’s worth it.
- Brewtarget: The best free brewing software I’m aware of. Not as comprehensive as BeerSmith, but gets the job done for many.