International Bitterness Units

About IBU 

IBU stands for International Bitterness Units and it is a measure for the bitterness of beer. 1 IBU is equal to 1 mg of iso-alpha acid per litre of beer. The IBU is calculated based on the amount of alpha acids in the hops used during the brewing process, and the time the hops are boiled in the beer. The longer the hops are boiled, the more bitterness they impart to the beer.

Although the IBU value is objective and measurable, the perception of taste can vary from beer to beer. 50 IBU measured in a Barley Wine with an initial specific gravity of around 1100 will not be perceived as bitter by the taster. A pilsner of 30 IBU, on the other hand, may be perceived as bitter. Our taste is a combination of all components in the beer. In the case of Barley Wine, the malty sweetness of residual sugars will overshadow the bitterness present. The message remains: taste, taste, and taste again.

How do you calculate IBU?

The calculation of IBU is actually quite complex and is often done using special software or formulas. But in simple terms: if you add more hops and let them boil longer, the beer will generally become more bitter and the IBU value will be higher. Brewers typically boil hops for about an hour and a half, due to the difficulty of extracting alpha acids from hops in the watery, sugar-rich wort with an almost neutral pH. The efficiency of iso-alpha acid extraction from alpha acids is usually less than 30%.

Hop efficiency, the measure indicating how efficiently alpha acids and other desired substances in hops are extracted and dissolved in the liquid during boiling, is difficult to measure due to the complex interplay of factors and variables. Professional brewers usually rely on modern analytical equipment to measure IBU, while amateur brewers have to rely on calculation formulas. Thanks to Glenn Tinseth's method, it is possible to calculate your IBU based on different variables. Curious about how much IBU your beer has or how much IBU your beer will have after brewing? Then you can use the information below to get started.

Get started!

This table provides insight into how different boiling times and initial specific gravities (SG) of the wort affect the extraction of alpha acids from hop cones.

Decimal hop efficiency in relation to boiling time and starting SG:

Boiling time in min.Starting SG
 103010401050106010701080109011001110
0000000000
30,0340,0310,0290,0260,0240,0220,020,0180,017
60,0650,0590,0540,0490,0450,0410,0380,0350,032
90,0920,0840,0770,0700,0640,0590,0540,0490,045
120,1160,1060,0970,0880,0810,0740,0680,0620,056
150,1370,1250,1140,1050,0960,0870,0800,0730,067
180,1560,1420,1300,1190,1090,0990,0910,0830,076
210,1730,1580,1440,1320,1200,1100,1010,0920,084
240,1870,1710,1570,1430,1310,1200,1090,1000,091
270,2010,1830,1680,1530,1400,1280,1170,1070,098
300,2120,1940,1770,1620,1480,1350,1240,1130,103
330,2230,2030,1860,1700,1550,1420,1300,1190,108
360,2320,2120,1940,1770,1620,1480,1350,1240,113
390,2400,2190,2000,1830,1670,1530,1400,1280,117
420,2470,2260,2060,1890,1720,1580,1440,1320,120
450,2530,2320,2120,1940,1770,1620,1480,1350,123
480,2590,2370,2160,1980,1810,1650,1510,1380,126
510,2640,2410,2210,2020,1840,1690,1540,1410,129
540,2690,2460,2240,2050,1880,1710,1570,1430,131
570,2730,2490,2280,2080,1900,1740,1590,1450,133
600,2760,2520,2310,2110,1930,1760,1610,1470,135
700,2850,2610,2380,2180,1990,1820,1660,1520,139
800,2910,2660,2430,2220,2030,1860,1700,1550,142
900,2950,2700,2470,2260,2060,1880,1720,1570,144
1200,3010,2750,2520,2300,2100,1920,1760,1610,147

Using the table, you can use the following formula:

IBU = gr/10l * a% * DHE (DHE = decimal hop efficiency)

Example 1

You have 20 litres of wort with an SG of 1070 that you boiled for 60 minutes with 100 grams of hop cones with an alpha acid percentage of 5.0%. The IBU value of the final beer will then be: (100/2.0) * 5.0 * 0.193 = 48.25.

Many brewers add hops at different times. In that case, calculate the IBU value for each hop addition and add the results together.

Example 2

Let's say you have 20 liters of wort with an SG of 1070. The wort boils for a total of 90 minutes. The wort is hopped at 3 different times:

30 grams of hops with an alpha acid percentage of 6% at the beginning of the boil;
30 grams of hops with an alpha acid percentage of 7% after 30 minutes of boiling;
10 grams of hops with an alpha acid percentage of 10%, 10 minutes before the end of the boil.

The IBU value of the final beer will then be: 

(30/2.0) * 6 * 0.206 = 18.54 

(30/2.0) * 7 * 0.193 = 20.27 

(10/2.0) * 10 * 0.070 = 3.5 

total = 42.31 

Of course, after such a calculation, you'll get an approximation of reality. For instance, the table "Decimal hop efficiency in relation to boiling time and initial SG" is optimized for brewing with hop cones. If you're using hop pellets, you should consider a higher hop efficiency of 10% to 15%.

The information about IBU is based on an article that was previously published in the magazine for amateur wine, beer, and liqueur makers, Proost, issue no. 16 and no. 17 in 1996.

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