This is a method used to estimate the bittering potential of hops. It is a simple equation that multiplies
the % Alpha Acids (by mass) and the total mass of the hop addition.
For a recipe with multiple hop additions, calculate the AAUs separately for each one, and then add the total AAUs together. The % Alpha Acids of a single hop variety depends on the harvest season, and will change from year to year. If you're trying to recreate a recipe, and the % Alpha Acids for the hops you used changed, the equation can calculate what mass to add to equal the same AAUs. If you want to make a particular recipe more or less bitter, add or subtract a few AAUs from the previous recipe, and calculate what mass to add.
This is a scale used to estimate the bitterness of a finished beer based on how the recipe was brewed. It ranges from 0-100, where 0 has no bitterness, and 100 has the most.
Calculating the IBUs has major factors, including the recipe's Alpha Acids Units (from above), how long hops are boiled, the specific gravity of the wort the hops are boiled in, and how many gallons the batch is. There are also minor factors in calculating the IBUs, including the form the hops are (whole, plug, pellet), the vigor of the boil, the vigor of the fermentation, how much attenuation and flocculation the yeast have, and how much the beer is filtered. But for starters, the base equation for calculating IBUs is below.
The AAUs and the volume are simple. The constant is just a result of converting units. But the utilization (U) is complicated, because it tries to calculate the remaining major and minor factors. There are a handful of people that have developed methods for estimating utilization. That list includes Ray Daniels, Mark Garetz, Randy Mosher, Jackie Rager, and Glenn Tinseth.
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