Authoritative content for precise results
Data Source and Methodology
Primary method: Tinseth IBU based on: Glen Tinseth, “The Relative Utilization of Alpha Acids from Hops,” 1997. Reference: RealBeer Hop Research (Archived). All calculations implement Tinseth’s utilization function with adjustments for pellet form and whirlpool temperature.
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Utilization U (Tinseth):
$$ U = 1.65 \\times 0.000125^{(SG - 1)} \\times \\frac{1 - e^{-0.04\\,t}}{4.15} $$
IBU per addition:
$$ \\mathrm{IBU} = \\frac{\\mathrm{AA} \\times W_{g} \\times 1000 \\times U \\times F_{form} \\times F_{wp}}{V_{L}} $$
Where:
- SG = specific gravity of the boil/wort (e.g., 1.050).
- t = boil time in minutes for the addition.
- AA = alpha-acid fraction (e.g., 0.10 for 10%).
- W_g = hop weight in grams.
- V_L = batch volume in liters.
- F_form = pellet factor (1.10 for pellet, 1.00 for whole leaf).
- F_wp = whirlpool temperature factor (0.02–1.0; see glossary).
Glossary of Variables
- Batch volume (V_L): Final post-boil volume into fermenter (L or US gal).
- Original gravity (SG/OG): Wort density before fermentation (e.g., 1.050).
- Alpha acid (AA%): Hop alpha acid percentage; enter as a percent (e.g., 10).
- Weight (W): Hop weight (g or oz). The calculator converts internally to grams.
- Boil time (t): Minutes the hops are boiled (0–120).
- Hop form factor (F_form): 1.10 for pellet, 1.00 for leaf/whole cone.
- Whirlpool factor (F_wp): Temperature-based reduction for non-boil isomerization. For example: 99–100°C ≈ 1.0, 90°C ≈ 0.6, 85°C ≈ 0.5, 80°C ≈ 0.3, 70°C ≈ 0.15, 60°C ≈ 0.05.
- BU:GU ratio: IBU divided by gravity units (GU = (OG − 1) × 1000).
Worked Example
How It Works: A Step-by-Step Example
Goal: 20 L batch, OG 1.050.
- Addition A: 25 g, 10% AA, pellet, 60 min boil.
- Addition B: 15 g, 10% AA, pellet, 10 min boil.
Bigness factor: $1.65 \\times 0.000125^{(1.050 - 1)} \\approx 1.65 \\times 0.000125^{0.050}$
Time factor at 60 min: $\\frac{1 - e^{-0.04 \\cdot 60}}{4.15}$; at 10 min: $\\frac{1 - e^{-0.04 \\cdot 10}}{4.15}$
Compute U for each, multiply by AA, weight, pellet factor (1.10), divide by 20 L, then sum IBUs.
Frequently Asked Questions (FAQ)
Which IBU method does this calculator use?
It implements the Tinseth method with optional pellet and whirlpool adjustments—an industry-standard approach for accurate homebrew planning.
How do whirlpool temperatures affect IBUs?
Isomerization slows as temperature drops below boiling. This tool applies a temperature factor so 80°C contributes less bitterness than 95–100°C for the same time.
Does leaf vs. pellet matter?
Yes. Pellet hops typically yield slightly higher utilization. We apply a 10% uplift when you choose pellet form.
Why is my measured IBU different from the estimate?
Kettle geometry, boil vigor, trub losses, and hop age can impact real IBUs. The model gives a close estimate; consider sensory evaluation and lab tests for exactness.
Can I enter additions at 0 minutes (flameout)?
Yes. Use 0 minutes as a boil addition (minimal bitterness) or choose Whirlpool and set your steep time and temperature for a more realistic estimate.
What BU:GU should I aim for?
It depends on style. For example, ~0.5–0.8 is typical for pale ales/IPAs, while malty styles may be lower. Always cross-check the target style guidelines.