IBU calculator
Bitterness comes from alpha acids isomerised in the boil, and how much isomerises depends on time and gravity.
%
minutes
%
minutes
%
minutes
Total bitterness
51.77IBU
- From the first addition
- 34.60 IBU
- From the second
- 17.17 IBU
- From the third
- 0.00 IBU
- Total hops
- 100.0
- Hopping rate
- 5.000 g/L
- Bitterness to gravity ratio
- 1.035
Show the working
- Batch volume = 20
- Boil gravity = 1.05
- First addition weight = 25
- First addition alpha = 12
- First addition boil time = 60
- Second addition weight = 25
- Second addition alpha = 12
- Second addition boil time = 15
- Third addition weight = 50
- Third addition alpha = 12
- Third addition boil time = 0
- bigness = 1.65 * 0.000125^(1.05 - 1) = 1.052 76
- u1 = 1.052 76 * (1 - exp(-0.04 * 60)) / 4.15 = 0.230 664
- u2 = 1.052 76 * (1 - exp(-0.04 * 15)) / 4.15 = 0.114 456
- u3 = 1.052 76 * (1 - exp(-0.04 * 0)) / 4.15 = 0
- From the first addition = 25 * 12/100 * 0.230 664 * 1000 / 20 = 34.5996
- From the second = 25 * 12/100 * 0.114 456 * 1000 / 20 = 17.1684
- From the third = 50 * 12/100 * 0 * 1000 / 20 = 0
- Total bitterness = 34.5996 + 17.1684 + 0 = 51.768
- Total hops = 25 + 25 + 50 = 100
- Hopping rate = 20 > 0 ? 100 / 20 : 0 = 5
- Bitterness to gravity ratio = 1.05 > 1 ? 51.768 / ((1.05 - 1) * 1000) : 0 = 1.035 36
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- IBU = sum over additions of weight x alpha x utilisation / volume
A zero-minute addition still contributes a little bitterness during the cool-down, which the model does not capture.