Using Hops: A Brief Guide


This section is a very short treatment of the subject of how to use hops.

Hops for Bittering

The bitterness in hops comes mainly from the alpha acids. As contained in the hops, the alpha acids are not very soluble. When boiled, the alpha acids begin to be converted into iso-alpha acids, which are much more soluble. The longer the boil, the more acids are converted. Also higher gravity worts use hops less effeciently. Because of these basic facts, most formulas for calculating the bitterness in your beer take these two factors into account. But there are lots of other factors that affect the final bitterness in your beer. Among them are: yeast strain/type, boil temperature, finings and filtration, to name a few.  Beer is rated for bitterness in IBUs, which stands for International Bittering Units. The IBU is roughly equivalent to milligrams of iso-alpha acids per liter of beer. Below is a fairly simple formula based on the one from the article by Jackie Rager in the Zymurgy 1990 Hops Special Issue. The formula has a "utilization factor" in it that you change for the length of your boil. We have adjusted the values from the original article to be more realistic, but if the resulting beer does not have the bitterness you want, make your own adjustment to the utilization factor accordingly.

Step 1. Gravity Adjustment

If the wort boil gravity is greater than 1.050, then you need to calculate the Gravity Adjustment (GA) factor for use in the bitterness calculations. If your gravity is below 1.050, then GA=0. To calculate the GA amount, use the following formula:

      Wort Gravity - 1.050   
GA =  ---------------------

So for example, if your wort gravity is 1.065, then GA= 1.065 minus 1.050 which is 0.015. 0.015 divided by 0.2 is .075 or .08 rounded up.

Step 2. Calculate Hop Amount for IBUs Desired

Using the utilization figure from the table, calculate the amount of hops (in ozs) to use to get the desired IBUs.

                Vol. in gal x (1+GA) x IBUs desired
Hop Wt in Ozs = ------------------------------------
                   %Util x % Alpha Acid x 0.749

Repeat this for each hop addition, if you add more than once, adding up the totals for the final IBU estimate for your beer. Lets say you want to make 5 gallons of pale ale at 30 IBUs with 1 bittering addition of Cascade hops at 6% alpha acid, with a 60 minute boil, with a gravity of 1.048. Since the gravity is less than 1.050, the gravity adjustment (GA) = 0. According to the formula, our first addition would be 5 * (1+0) * 30 divided by 21 * 6 * 0.749 which totals 1.58 ozs.

Boil Time % Util
< 6 min. 0%
6-10 min. 0%
11-15 min. 2%
16-20 min. 5%
21-25 min. 8%
26-30 min. 11%
31-35 min. 14%
36-40 min. 16%
41-45 min. 18%
46-50 min. 19%
51-60 min. 20%
61-70 min. 21%
71-80 min. 22%
81-90 min. 23%
Average Hop Utilization Based on Boil Time

Hops for Aroma

Hops also contain essential oils that are responsible for the hop aroma and hop character in beer. The aroma is lost because wort boiling process causes the oils to evaporate. The longer the hops are boiled, the less aroma components remain. To get some hop aroma in the beer, brewers add hops very late in the boil. Some add them even after the boil, steeping them as the wort cools. The heat of the hot wort in all these cases changes the aroma profile of the oil - partially because some compounds evaporate, but chemical changes also occur. So even if lots of the aroma compounds remain, the actual aroma will be quite different than the aroma of fresh hops. To get the aroma of fresh hops in beer, hops are added very late in the process, usually during conditioning. Since there is no heat, the aroma remains unchanged. This process is known as "dry hopping". The process of adding fresh hops to hot wort (for aroma) is variously known as late kettle hopping, late addition hopping or finish hopping. As you can tell from the table, you can largely ignore the alpha acid content of the hops used for boil times less than 10-15 minutes, steeped or dry hopped. What serves as a guide to hop aroma and character is the oil content. Our hops are all rated for oil content. How do you use the oil content as a guideline for getting consistent aroma effects? Unlike the IBU, no standard yet exists for a measurement of aroma. The best method for the homebrewer is to keep accurate records of your aroma hop additions. Important data points to record are: time of addition, quantity of hops, and the oil content percentage of the hops used. When you get an effect you like, you can now repeat it closely, assuming you use hops of the same variety and with the same oil content. If the oil content is different, you'll need to adjust the amount of hops used according to the following formula:

                Original Oil Content
New Hop Qty  = --------------------- x Original Hop Qty
                   New Oil Content

Note that you should treat the results of this formula as a guideline, not an absolute. Why? Because sometimes the "hoppiness" of a hop doesn't always track the oil content exactly. But oil content rated hops will certainly provide a step in the right direction.