Obtaining the Desired Bitterness

Once you have determined how many pounds of fermentables are necessary for your recipe, you will need to determine the amount of hops you want to use. Different styles of beer call for different hop profiles. Bieres de Garde should have very little hop character, while an India Pale Ale should have loads. Likewise, Cascade hops would be right at home in an American pale ale, but would be completely out of character in a traditional Czech pilsner where Saaz hops should be prevalent.

Below is a chart of the common hop varieties, their common alpha acid percentage range, their primary uses, the styles of beer in which they are traditionally brewed and other hops that you can substitute for them. Keep in mind that some hops are better for bittering than flavoring or aroma and vice-versa. Furthermore, some hops are more traditionally used in one style of beer rather than another. However, you should feel free to experiment. For example, although Chinook hops are most often used for bittering due to their high alpha acid content, they are know to be very intense in aroma and are occasionally used accordingly.

Once you know what type of hops you want to add to your brew, just like with the fermenatables, you need to know how much to add. You can refer to the first chart on this page to review the IBUs appropriate for each styles of beer. After you figure out how bitter you beer should be, you need to determine how much hops to use to reach that target bitterness. Hop flavor and aroma are too subjective to create hard and fast rules about how much hops should be used for each. I suggest that you simply refer to another recipe you liked until you are experienced enough to know how much flavoring and bittering hops to use. Otherwise, experiment with it. Therefore, this section will be concerned only with helping you reach a target bitterness.

There are two primary methods used to determine the hop bitterness of beer - HBUs and IBUs. IBUs, although more complicated to calculate, are a more accurate measurement.

Homebrew Bittering Units (HBUs)

Because of the ease in calculating HBUs, this is the method of measuring hop bitterness most commonly used by homebrewers. The formula is below. All you need to know is the alpha acid percentage and the amount of the hops you intend to use.

HBUs are simply obtained by multiplying the alpha acid percentage of the bittering hop by the ounces of hops boiled for more than 15 minutes. For example, if 2 ounces of hops with 9% alpha acid percentage are boiled for more than 15 minutes, the beer would have 18 HBUs. However, this measurement only approximates actual bitterness as hops boiled for 20 minutes don't contribute as much bitterness as hops boiled for 60 minutes.

The formula can also work in reverse. Suppose you know that the beer you want to brew has 18 HBUs. The first step would be determining the type of hops you want to use. Say you want to use Centennial hops with an alpha acid percentage of 9.0%. Just do the formula in reverse - divide the 18 HBUs by the 9.0% alpha acid percentage. You'll learn that you'll need to boil 2 ounces of Centennial hops for more than 15 minutes.

The same holds true even if you're using more than one hop variety and staggered hop additions. Suppose you still want 18 HBUs, you bitter with 1 ounce of 9.0% Centennials and you add 6.0% Cascades for flavoring at 16 minutes remaining in the boil. Half of your HBUs are already accounted for by the Centennials, so you only need to use the formula for 9 HBUs. Using the formula, we can figure out that we will need to use 1-1/2 ounces of the Cascades to reach the target HBUs.

International Bittering Units (IBUs)

The accepted worldwide standard for measuring bitterness in beer, IBUs are based on the estimated alpha acid percentage of the hops used and the length of time they are boiled. One IBU equals 1 milligram of isomerized alpha acid in 1 liter of wort or beer. IBUs are calculated using a slightly more complex formula than HBUs:

The percent utilization of a hop is a function of its boil time. The longer the boil, the more bitterness the hop imparts. Sorry, but another chart will help explain this concept.

The percent utilizations in the above list are approximations. Factors that will increase the percent utilization include high wort pH, long boil times, low wort gravity, using fresher hops and the strain of yeast used. Factors that decrease percent utilization include low wort pH, short boil times, high wort gravity, using hop bags, using stale hops and the strain of yeast used. However, hop utilization rarely ever goes over 30%.

Using the above information, we can determine the IBUs of our prospective beer. For example, taking the same hypothetical beer as before, if we boiled 1 ounce of 9.0% Centennials for 60 minutes and 1-1/2 ounce of 6.0% Cascades for 16 minutes, we would have to run two calculations as follows:

Then,

Adding the two totals together, the total IBUs for this hypothetical batch of beer is approximately 50 - a pretty hoppy beer. Understanding the concept of percent utilization will help you realize why using HBUs are unreliable in terms of identifying the actual bitterness of your beer.