A rather simplified Whirlpool Hop IBU computation method

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For Whirlpool Temperature in degrees C:

IBU Reduction Factor C. degrees = (2.39*10^11*2.71828182846^-(9773/(Temperature+273.15)))*1/1.009231744

For Whirlpool Temperature in degrees F:

IBU Reduction Factor F. degrees = (2.39*10^11*2.71828182846^-(9773/((Temperature-32)/1.8+273.15)))*1/1.009231744

Step 1) Simply copy either of these two formulas directly into your computers scientific calculator and replace "Temperature" with your Whirlpool temperature of choice.

Step 2) Next multiply the nominal "sea level" IBU's indicated via your IBU calculator of choice by the derived reduction factor to compute Whirlpool derived IBU's.

Example:

Let's presume that for 30 minutes of boiling a given weight and AA strength of hop, with a sea level boiling temperature of 212 degrees F. your IBU calculator of choice derives IBU's at 90.

Now let's ask how many IBU's we should nominally evolve from the very same weight of Hops at the very same AA strength, when Whirlpooled at 185 degrees F. for 30 minutes.

IBU Reduction Factor F. degrees = (2.39*10^11*2.71828182846^-(9773/((Temperature-32)/1.8+273.15)))*1/1.009231744
IBU Reduction Factor F. degrees = (2.39*10^11*2.71828182846^-(9773/((185-32)/1.8+273.15)))*1/1.009231744
IBU Reduction Factor F. degrees = 0.3339

90 IBU's computed for sea level x 0.3339 = 30.05 IBU's computed for Whirlpooling at 185 degrees F.

 

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This method can also be used whereby to compute boil IBU's for elevations differing from sea level. All you need to determine is the nominal elevation adjusted boiling temperature of water for your brewing locations elevation.

For degrees F.:
Adjusted Boil Temp = 49.161 * LN(29.921 * (1 - 0.0000068753 *Elevation_Feet)^ 5.2559) + 44.932

For degrees C.:
Adjusted Boil Temp = ((49.161 * LN(29.921 * (1 - 0.0000068753 *Elevation_Meters/0.3048)^ 5.2559) + 44.932)-32)/1.8

Once again, copy the equation into your computers scientific calculator and change "Elevation_xxxx" to your locations elevation in feet or meters.

 

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Approximate IBU's reduction from uncompensated computation for various brewing elevations above sea level:

Sea Level = 0% Reduction
100 Ft. ~= 0.7% Reduction
250 Ft. ~= 1.7% Reduction
500 Ft. ~= 4.4% Reduction
1,000 Ft. ~= 6.7% Reduction
1,500 Ft. ~= 9.1% Reduction
2,000 Ft.~= 13.1% Reduction
2,500 Ft. ~= 16.1% Reduction
3,000 Ft. ~= 19% Reduction
3,500 Ft. ~=21.9% Reduction
4,000 Ft. ~= 24.7% Reduction
4,500 Ft. ~= 27.4% Reduction
5,000 Ft. ~= 30% Reduction
5,500 Ft. ~= 32.6% Reduction
6,000 Ft. ~= 35% Reduction
7,500 Ft. ~= 42% Reduction
10,000 Ft. ~= 52.2% Reduction
12,500 Ft ~= 60.8% Reduction

 

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Whirlpooling is much like boiling ones wort at a given elevation above sea level, with the main difference being that Whirlpooling induces zero boiling loss.

For example:
One person brewing at about 14,350 feet of elevation (while wearing an oxygen mask, one would hope) and another person Whirlpooling at 185 degrees F. are right close to being the same as to their process generated IBU's, sans for the impact of boil-off upon IBU's.