Tinseth’s IBU Formula
IBUs = decimal alpha acid utilization * mg/l of added alpha acids
Tenseth’s base formula is simple enough, We just need to solve for our mg/l of alpha acids and decimal alpha acid utilization% to find our brews estimated IBU.
mg/l of added alpha acids = (decimal AA rating * ozs hops * 7490) / gallons of wort
Decimal Alpha Acid Utilization = Bigness Factor * Boil Time Factor
Bigness factor = 1.65 * 0.000125^(wort gravity – 1)
Boil Time factor = (1 – e^(-0.04 * time in mins) )/4.15
**Note: e = 2.71828
Tenseth’s Formula Example
Batch Information
Pre-Boil Volume: 6.5 gallons
Target Batch Size: 5 gallons
Original Gravity: 1.050
Hop Additions
1.5oz Hops – 6.4% AA @ 45 mins
1 oz Hops – 5% AA @ 15 mins
The nice thing about Tenseth’s formula is that it can easily be broken down into smaller components. We just have to solve the foundation equations, then we can plug in our variables to find our IBU for the example beer recipe above.
mg/l of added alpha acids:
(.064 * 1.5oz * 7490) / 5 = 143.808
(.050 * 1oz * 7490) / 5 = 74.9
Next we need to solve for our Decimal Alpha Acid Utilization by solving for our Bigness Factor and Boil Time Factor:
Bigness factor:
1.65 * 0.000125^(1.05- 1) = 1.052
Boil Time factor:
Hop Addition #1: (1 – 2.71828^(-0.04 * 45))/4.15 = .201
Hop Addition #2: (1 – 2.71828^(-0.04 * 15))/4.15 = .108
Now we can go ahead and solve for Utilization % for our hop additions.
Hop Addition #1:1.052 * .201 = .211
Hop Addition #2:1.052 * .108 = .113
IBUs = decimal alpha acid utilization * mg/l of added alpha acids
Hop Addition #1: .211 * 143.808 = 30.34 IBU’s
Hop Addition #2: .108 * 74.9 = 8.08 IBUs
30.34+8.08=38.42 Total IBUs
Calculation
A simplified equation from Ray Daniel’s Book Designing Great Beers for IBUs is:
- IBUs = U% * (ALPHA% * W_OZ * 0.7489) / (V_Gal)
Where:
- U% is the hop utilization in percent
- ALPHA% is the percent alpha for the hop variety
- W_OZ is the hop weight in ounces
- V_GAL is the volume of hops in gallons.
...
Example:
Boil Size | 13.82 Gal |
---|---|
Pre Boil OG | 1.058 |
OG | 1.062 |
Amount | 2 oz |
Alpha | 8.2% |
Time | 60 min |
IBUs = U% * (ALPHA% * W_OZ * 0.7489) / (V_Gal)
= U% (0.082 x 2 x0.7489 ) / 13.8 gal
=
References
Reference | URL |
---|---|
Calculating Hop Bitterness: How much Hops to Use? | https://beersmith.com/blog/2008/04/20/calculating-hop-bitterness-how-much-hops-to-use/#:~:text=A%20simplified%20equation%20from%20Ray,*%200.7489)%20%2F%20(V_Gal) |
BITTERNESS (IBU) CALCULATOR | https://www.hopsteiner.com/ibu-calculator/ |
Bitterness Calculator | http://www.realbeer.com/hops/bcalc_js.html |