International Bitterness Units (IBU) and Maximum IBU (MIBU) Calculations
The International Bitterness Unit, or IBU for short, was introduced in the 1950s and 1960s to quantify a beer’s perceived bitterness. Today, IBUs are used by brewers to develop new recipes and to maintain consistent bitterness levels in their beers. However, the IBU range, typically between 5 and 120, does not fully reflect bitterness’s quality or overall perception.
One of the most commonly used IBU calculation formulas is the Tinseth formula, developed by Glen Tinseth in 1997. Other formulas include Rager, Garetz, Mosher, Noonan, and Daniels. These formulas differ in how they approach hop utilization. However, due to changes in brewing practices, hops used today are different from those used in the past, making the IBU range less accurate than it used to be.
A more accurate way to calculate IBU contribution is through the use of Maximum International Bitterness Units, or MIBUs. This calculation, developed by Paul-John Hosom in 2015, is an adaptation of the Tinseth formula that takes into account post-boil bitterness contributions from additional equipment and process parameters, such as pot size, cooling method, hop stand procedure, and hop temperature. This leads to a more precise prediction of IBU contribution over time.
How is MIBU Calculated?
MIBU takes into account various stages of the brewing process, such as the boil, hop stand, and cooling phases. The formula calculates the rapid IBU contribution for each time constant based on wort temperature and volume increments during each period and sums up all the results to find the total IBU contribution for each hop addition.
What Makes MIBU More Accurate?
MIBU considers carry-over bitterness contributions from boil additions in the hop stand, residual bitterness contributions from both boil and hop stand hops during the cooling phase, changes in volume due to evaporation during the boil, and the alpha-acid solubility limit when a large amount of hops is added. Additionally, MIBU has the option to use advanced pellet processing, which improves upon the traditional method of using an expanding factor. It also provides a chart to visualize bitterness contributions over time for all hop additions.