Bitterness

Bitterness – hop. This is the most common connection in most styles of beer.
This connection between bitterness and hop is becouse the bitterness is provided by alpha-acid content from hops during brewing.
The important thing here is the utilisation – the efficiency of isomerization of alpha acid as a function of time – how much alpha acid comes from the hops to the wort.
The utilisation depends on:
– format of hops
– the age of hops
– lenght of boil (utilisation increases with increasing boil lenght)
– gravity of boil (utilisation decreases with increasing wort gravity)
– intensity of oil (utilisation increases with increasing intensity of boil)
– quality of hops (utilisation increases with better quality)

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1. Units

AAU (Alpha acid units – the amount of alpha acid in given weight of hops; the bitterness potential of hops)
IBU (International Bitterness Units – the bitterness is measured with)
Utilisation – U (the efficiency of isomerization of alpha acid as a function of time – how much alpha acid comes from the hops to the wort; we use the table with utilisation values – point 3)
AA% (Alpha Acid percentage in hops – you get this data from hop supplier

2. Equations

Equations for US units:
AAU = (AA %) x (Weight of Hops in ounces)

IBU = ((Weight of Hops in ounces) x (AA %) x (Utilisation decimal) x 74,9) / (Volume (final) in gallons)

…for metric units:
AAU = (AA %) x (Weight of Hops in grams x 0,0353)
IBU = ((Weight of Hops in grams) x (AA %) x (Utilisation decimal) x 10) / Volume (final) in liters

3. Utilisation values

Decimal Alpha Acid Utilisation vs. Boil Time and Wort Original Gravity

Original Gravity →
Time (minutes) ↓
1,0301,0401,0501,0601,0701,0801,0901,1001,1101,1201,130
00,0000,0000,0000,0000,0000,0000,0000,0000,0000,0000,000
30,0340,0310,0290,0260,0240,0220,0200,0180,0170,0150,014
60,0650,0590,0540,0490,0450,0410,0380,0350,0320,0290,026
90,0920,0840,0770,0700,0640,0590,0540,0490,0450,0410,037
120,1160,1060,0970,0880,0810,0740,0680,0620,0560,0520,047
150,1370,1250,1140,1050,0960,0870,0800,0730,0670,0610,056
180,1560,1420,1300,1190,1090,0990,0910,0830,0760,0690,063
210,1730,1580,1440,1320,1200,1100,1010,0920,0840,0770,070
240,1870,1710,1570,1430,1310,1200,1090,1000,0910,0830,076
270,2010,1830,1680,1530,1400,1280,1170,1070,0980,0890,082
300,2120,1940,1770,1620,1480,1350,1240,1130,1030,0940,086
330,2230,2030,1860,1700,1550,1420,1300,1190,1080,0990,091
360,2320,2120,1940,1770,1620,1480,1350,1240,1130,1030,094
390,2400,2190,2000,1830,1670,1530,1400,1280,1170,1070,098
420,2470,2260,2060,1890,1720,1580,1440,1320,1200,1100,101
450,2530,2320,2120,1940,1770,1620,1480,1350,1230,1130,103
480,2590,2370,2160,1980,1810,1650,1510,1380,1260,1150,105
510,2640,2410,2210,2020,1840,1690,1540,1410,1290,1180,108
540,2690,2460,2240,2050,1880,1710,1570,1430,1310,1200,109
570,2730,2490,2280,2080,1900,1740,1590,1450,1330,1210,111
600,2760,2520,2310,2110,1930,1760,1610,1470,1350,1230,112
700,2850,2610,2380,2180,1990,1820,1660,1520,1390,1270,116
800,2910,2660,2430,2220,2030,1860,1700,1550,1420,1300,119
900,2950,2700,2470,2260,2060,1880,1720,1570,1440,1320,120
1200,3010,2750,2520,2300,2100,1920,1760,1610,1470,1340,123

4. Calculation

How to calculate bitterness?


Example:

Original gravity is 1,054, we will use 20 grams/0,705 oz Challenger 7% AA  (60 minutes), 15 grams/0,53 oz East Kent Golding 4% AA (15 minutes), 15 grams/0,53 oz East Kent Golding 4% AA (3minutes) for the final volume 20 liters/5,28 gal.

Step 1: becouse 1,054 is not in a table, we will calculate approximation
Between 1,050 and 1,060 there are 10 points, so we will devide the values from table (utilisation) between those values on 10 sections (for each hop and time), and calculate this approximation:

U(Challenger) = 0,231 – 0,211 / 10 = 0,002
For 1,054 (60 min) is value from the table for 1,050 (0,231) plus 4 points x 0,002 (0,008), so to sum up the U(1) value is 0,231 + 0,008 = 0,239

U(East Kent Golding) = 0,114 – 0,105 / 10 = 0,0009
For 1,054 (15 min) is value from the table for 1,050 (0,114) plus 4 points x 0,0009 (0,0036), so to sum up the U(2) value is 0,114 + 0,0036 = 0,1176

U(East Kent Golding_2) = 
0,029 – 0,026 / 10 = 0,0003
For 1,054 (3 min) is value from the table for 1,050 (0,029) plus 4 points x 0,0003 (0,0012), so to sum up the U(3) value is 0,029 + 0,0012 = 0,0302

Step 2: calculate bitterness for each hop addition

Metric units:
IBU(Challenger) = 20 g x 7 % x 0,239 x 10 / 20 l = 16,7
IBU(East Kent Golding) = 15 g x 4 % x 0,1176 x 10 / 20 l = 3,5
IBU(East Kent Golding_2) = 15 g x 4 % x 0,0302 x 10 / 20 l = 0,9

US units:
IBU(Challenger) = 0,705 oz x 7 % x 0,239 x 74,9 / 5,28 gal = 16,7

IBU(East Kent Golding) = 0,5295 oz x 4 % x 0,1176 x 74,9 / 5,28 gal = 3,5
IBU(East Kent Golding_2) = 0,5295 oz x 4 % x 0,0302 x 74,9 / 5,28 gal = 0,9

Step 3: sum up the hop bitterness shares and you have IBU

IBU = 16,7 + 3,5 + 0,9 = 21,1

Now we learned how to calculate bitterness level!

If you use pellets the recommended reduction for hop weight is by 25 % !