The balance between sweet malt and bitter hop flavours is a defining characteristic of most beer. It’s essential you think about this if you want to control the taste of your home brew.
But how can you measure this balance?
Beer recipes usually contain target original and final gravities alongside International Bittering Unit (IBU) values.
Gravity describes the quantity of sugar required, usually produced with malted barley, while IBUs are an indication of the bitterness provided by hops.
(If you’re already lost check out this page describing the basic ingredients used to make beer).
Although this information can help you determine quantities of malt and hops, it doesn’t tell you anything about balance.
That’s what is actually important: whether a beer tastes bitter or not.
To understand this difference think of two beers.
One is high gravity with lots of hop bitterness. The second has half the gravity with the same amount of hops.
To taste, the second is twice as bitter. The effect of the hops is stronger.
This is where the bitterness ratio comes in. It describes the relationship between bitterness and gravity, regardless of the actual numbers.
It tells you whether a beer is broadly bitter or broadly sweet.
Calculating Beer Bitterness Ratios
There are several ways to calculate bitterness ratios.
The simplest, and most frequently used, has been explained by Brad Smith.
He describes a method that compares original gravity with bittering units using this formula:
This is the BU:GU ratio.
I’ll use this porter recipe to show you how it works. The beer has:
- Original Gravity 1.056
- IBUS 30
First convert the gravity figure into gravity points. That’s a simple matter of removing the 1 and multiplying by a thousand.
Use this formula:
In my example beer this comes out as:
Now use the first formula to work out your bitterness ratio:
0.5 is considered average. Beers with a bitterness ratio above this are more bitter, and those below are sweeter.
This porter then, is slightly more bitter than usual.
So far, so good. This tells us about the bitterness ratio, but what you really need to know is how this can help you design beer recipes.
Bitterness Ratios For Different Beer Styles
The BJCP has published style guidelines for more or less every beer from across the world.
Although brewing within such rigid boundaries is mainly for those entering competitions, the document is a very handy port of call when planning your own beer recipes.
When looking at bitterness ratios, you’re interested in original gravity and bitterness. The guide gives these as a range so first you have to work out the average.
Let’s say you want to find out the bitterness ratio of the average brown porter.
Original gravity is between 1.040 and 1.052:
An average of 1.046, or 46 points.
And the IBUs are between 18 and 35:
An average of 26.5.
With this you can work out the bitterness ratio:
My porter recipe, with a ratio of 0.54, is slightly less bitter than average.
Knowing this you may decide to add a few more hops to compensate, if you’re shooting for dead on style.
Proof That Bitterness Ratios Are Worth Bothering With
Notice that if you had just compared the raw number of bittering units you would have guessed that my porter was more bitter than most. It has 30 IBUs against the 26.5 IBU average.
Bitterness is relative to the sweetness of malt, and IBUs alone don’t take that into account.
Beer Bitterness Ratio Chart
You can use this chart to compare each style:
If you prefer, there is a pdf here.
Relative Bitterness and the BU:RE Ratio
As I was putting this page together I began thinking that something’s not right.
Brad Smith points out that the bitterness ratio alone doesn’t convey the full picture. Roasted malts also have bitter flavours that alter the taste, for example.
But the thing that was bugging me was the lack of consideration of attenuation, which is another way of saying the amount of sugar that’s consumed during fermentation.
Using another two hypothetical beers as an example:
- O.G. of 1.100, FG of 1.030, IBUs 50
- O.G. of 1.100, FG of 1.010, IBUs 50
The only difference is the final gravity, the sugar left in the beer after fermentation.
Beer 2 would taste more bitter because it has less residual sweetness, yet the BU:GU ratio would be the same:
After digging around I discovered that I wasn’t the only one to have noticed this. In fact, the Mad Alchemist has proposed an interesting alternative system for measuring bitterness ratios.
His method compares IBUs with gravities using this formula:
The complicated looking bottom line uses the formula for calculating real extract, an accurate way of measuring attenuation.
This time gravity is in °Plato which can be determined like this:
The alternative ratios are on a scale of 1 to 10.
This is how that compares with the BU:GU ratio:
Bear in mind that I multiplied the BU:GU ratio 10 to make comparison easier.
The overall pattern is similar but the beers you’d expect to be more bitter, such as Imperial IPA or Special Bitter, now have a higher bitterness ratio.
Although it still doesn’t allow for other factors such as astringent roast malt, it’s a more robust method of calculation.
My Own Beer Bitterness Ratio
Before I found the Mad Alchemist’s (convincing) technique I had already developed my own bitterness ratio to deal with my doubts about BU:GU.
It’s a half-way point between the two.
Like BU:GU it works with simple gravity information from the style guide, but it takes into account final gravity as well.
Here’s how that comes out in chart form:
You can get a pdf here.
The numbers are higher, but the pattern between beers is similar and this ratio deals with differences in final gravity.
I’m still testing this when I brew.
What do you think of the method? Let me know in the comments.
Using The Bitterness Ratios
The main thing to remember with all of this is that you’re controlling the balance of beer flavours between sweet and bitter. It’s up to you where you want your beer to fall on the scale.
As long as you understand what the figures mean and can relate them to beer, that’s OK.