Challenger hop IBU calculator
Challenger averages about 7.5% alpha acid, though every harvest is different and the actual figure is printed on the packet — use that one.
- Hops needed for the target IBU
- 46.24
- Alpha acid utilisation
- 23.066 %
- IBU per gram in this batch
- 0.8650
- Alpha acid units
- 7.937
- Bitterness to gravity ratio Around 0.5 is balanced; above 0.8 is a bitter beer.
- 0.519
- Gravity factor
- 1.052 76
- Time factor
- 0.219 10
Show the working
- Hop weight = 30
- Alpha acid = 7.5
- Boil time = 60
- Batch volume = 20
- Boil gravity = 1.05
- Target bitterness = 40
- Gravity factor = 1.65 * 0.000125^(1.05 - 1) = 1.052 76
- Time factor = (1 - exp(-0.04 * 60)) / 4.15 = 0.219 104
- utilisation = 1.052 76 * 0.219 104 = 0.230 664
- Bitterness = 20 > 0 ? 30 * 7.5/100 * 0.230 664 * 1000 / 20 : 0 = 25.9497
- Hops needed for the target IBU = 0.230 664 > 0 && 7.5 > 0 ? 40 * 20 / (7.5/100 * 0.230 664 * 1000) : 0 = 46.2433
- Alpha acid utilisation = 0.230 664 * 100 = 23.0664
- Alpha acid units = 30 / 28.349523125 * 7.5 = 7.936 64
- IBU per gram in this batch = 20 > 0 ? 7.5/100 * 0.230 664 * 1000 / 20 : 0 = 0.864 99
- Bitterness to gravity ratio = 1.05 > 1 ? 25.9497 / ((1.05 - 1) * 1000) : 0 = 0.518 994
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
- Tinseth utilisation = bigness factor x boil time factor
- bigness = 1.65 x 0.000125^(gravity - 1)
- time factor = (1 - e^(-0.04 t)) / 4.15
- IBU = weight x alpha x utilisation / volume
Tinseth is an empirical fit to measured beers, not a physical model. Real IBU can differ by 20% from any prediction, and measured IBU does not perfectly track perceived bitterness either.
Alpha acid degrades in storage. Hops kept warm and exposed to air can lose half their alpha in a year.
Whirlpool and dry hop additions contribute very little measured IBU but a great deal of aroma.
Challenger utilisation by boil time
| Boil time | Utilisation at 1.050 | IBU from 30 g in 20 L |
|---|---|---|
| 0 min | 0.00% | 0.0 |
| 5 min | 4.60% | 5.2 |
| 10 min | 8.36% | 9.4 |
| 15 min | 11.45% | 12.9 |
| 20 min | 13.97% | 15.7 |
| 30 min | 17.73% | 19.9 |
| 45 min | 21.17% | 23.8 |
| 60 min | 23.07% | 25.9 |
| 90 min | 24.67% | 27.8 |
Frequently asked
What is the alpha acid of Challenger?
Typically around 7.5%, but check the packet — it varies by harvest and by several percentage points.
How much Challenger do I need for a bitter beer?
Set your target IBU above and the calculator gives the weight for a 60-minute addition at your batch size and gravity.
Where the numbers come from
- Utilisation model from Glenn Tinseth; alpha acid figures are typical published ranges for the variety.