A technical discussion of bitterness units, formulas for estimating bitterness, and bitterness adjustments associated with various hop uses supported in BeerSmith.
The International Bitterness Unit (IBU) [Also called EBU] is the standard for measuring the bitterness contribution of various hop additions to beer. An IBU is defined as 1 mg of iso-alpha-acid per liter of solution. Several methods (listed below) based on the boil time, amount added, alpha acid of the hops, volume of the beer and gravity of the wort attempt to estimate the total bitterness contributed to the beer.
While IBUs provide the most reliable measurement of total bitterness, they are obviously only part of the hops flavor profile. Different hop varieties impart slightly different flavor and aroma profiles to the beer.
Two other commonly used measures are Alpha Acid Units (AAU) and Home Bitterness Units (HBU). These measures take into account only the alpha acid and amount of hops added and are considered inferior to IBUs because they do not account for boil time. The formula for each is:
In both instances, only hops boiled for 15 minutes or more is included in the calculation. BeerSmith calculates total AAUs for a recipe for compatibility, but we recommend using IBUs in recipe formulation wherever possible.
There are three popular formulas for calculating IBU bitterness. These are Rager, Tinseth and Garetz, with each named after the last name of the formula's author. Each formula calculates detailed hop utilization based on boil time, volumes, wort gravity, alpha acid, etc.
The formulas and tables used to calculate utilization are quite long, but a full discussion can be found at the following web locations/references:
Rager's method is the oldest, and generally results in the highest utilization numbers. Garetz's formula takes into account more factors and results in slightly lower overall utilization, but no utilization for very small boil times.
Glenn Tinseth's method is considered by many to be the most accurate, and is in fact the default method used in BrewSmith.
BeerSmith allows any of the three methods to be used when calculating bitterness. You can set the method to be used for calculating the bitterness of recipeson the Bitterness tab of the Options command under the Tools menu.
Additional adjustments are available depending on the type of hops (plug, whole, pellet) and the use of the hops. All can be adjusted from the Bitterness tab of the Options command on the Tools menu.
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