IBU's to AAU's
- Thread starter JoeBo
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How to Brew -By John Palmer:
The first step is to calculate the Alpha Acid Units (AAUs).
AAU = Weight (oz) x % Alpha Acids (whole number)
AAU (60) = 1.5 oz x 6.4 = 9.6 AAUs of Perle and AAU (15) = 1 oz x 4.6 = 4.6 AAUs of Liberty
Whenever a brewer is using AAUs in a recipe to describe the quantity of hops, it is important to specify how long each addition is boiled. The boiling time has the largest influence on how bitter a hop addition makes the beer. If no times are specified, then the rule of thumb is that bittering hops are boiled for an hour and finishing hops are boiled for the last 10-15 minutes. Many brewers add hops at 15 or 20 minute intervals and usually in multiples of a half ounce (for ease of measurement).
To calculate how much bitterness the final beer will have from these hop additions, we apply factors for the recipe volume (V), gravity of the boil and the boil time. The time and gravity of the boil are expressed as the utilization (U). The equation for IBUs is:
IBU = AAU x U x 75 / Vrecipe
75 is a constant for the conversion of English units to Metric. The proper units for IBUs are milligrams per liter, so to convert from ounces per gallon a conversion factor of 75 (74.89) is needed. For the metric world, using grams and liters, the factor is 10. (For those of you paying attention to the units, the missing factor of 100 was taken up by the % in the AAU calculation.)
The first step is to calculate the Alpha Acid Units (AAUs).
AAU = Weight (oz) x % Alpha Acids (whole number)
AAU (60) = 1.5 oz x 6.4 = 9.6 AAUs of Perle and AAU (15) = 1 oz x 4.6 = 4.6 AAUs of Liberty
Whenever a brewer is using AAUs in a recipe to describe the quantity of hops, it is important to specify how long each addition is boiled. The boiling time has the largest influence on how bitter a hop addition makes the beer. If no times are specified, then the rule of thumb is that bittering hops are boiled for an hour and finishing hops are boiled for the last 10-15 minutes. Many brewers add hops at 15 or 20 minute intervals and usually in multiples of a half ounce (for ease of measurement).
To calculate how much bitterness the final beer will have from these hop additions, we apply factors for the recipe volume (V), gravity of the boil and the boil time. The time and gravity of the boil are expressed as the utilization (U). The equation for IBUs is:
IBU = AAU x U x 75 / Vrecipe
75 is a constant for the conversion of English units to Metric. The proper units for IBUs are milligrams per liter, so to convert from ounces per gallon a conversion factor of 75 (74.89) is needed. For the metric world, using grams and liters, the factor is 10. (For those of you paying attention to the units, the missing factor of 100 was taken up by the % in the AAU calculation.)
