The science behind bitterness: How is Ibus level calculated?
In the world of beer manufacturing, one of the aspects that most fascinate fans and experts equally is the perception of bitterness. To quantify that feeling, the brewers resort to the figures of Ibus, but the way in which they are estimated and measured has much more to do with mathematics than with the direct sensory experience.
Behind the formulas: what is in the numbers?
There are several widely known methodologies to predict the amount of Ibus in a recipe, including the formulas of Tenseth, Garetz and Rager. These follow a similar logic: they consider the boiling time, the volume of must, the amount of hops and the percentage of alphaacids to estimate bitterness. The fundamental difference is how they calculate the hops use factor, a key element in the equation.
From these formulas, the brewers obtain a value for each must of hops, adding them to approximate the total level of IBUS of the final product. It is also possible to include the effect of whirlpool and other humification techniques.
What really do those Ibus figures really mean?
In spite of the variety of formulas and methods, a frequent doubt revolves around whether these numbers correspond to a measure of bitterness in beer already bottled or if, in reality, they represent an estimate prior to fermentation.
To clear these doubts, I consulted Glenn Tenseth, creator of the formula that bears his name, in an ancient episode of a specialized podcast. His response was simple but revealing: the values used in his equation correspond to Ibus measured before yeast does his magic during fermentation.
It is important to understand that during that stage, some of the substances responsible for bitterness, isomerized alphaacids, suffer losses, so the final amount in beer can be less than the initially estimated.
The Ibus in style guides and their reality
What about the Ibus that appear in the style guides, those used by judges and brewers to define categories? There is also an interesting fact: in general, the values that are published there are estimates, not direct measurements.
Conversing with Gordon Strong, president of the Association of Artisan Brewers, he explained that these figures are based on estimates, not on precise analysis. That is, they serve as a reference to maintain coherence in the design of recipes and for classification, but real beer can show much lower IBUS levels when measured in a laboratory.
What implies all this for brewers and fans?
At first, it may seem disconcerting to think that the figures we admire in the recipes or in the guides are only approaches. However, if they are taken as guide tools for the creation process, they have a very valuable function. The key is to understand that predictive Ibus are a concept more than an exact measurement of the final product.
While for the great professional breweries and laboratories, measure the IBUS with precision can be routine, for the homemade and artisanal scene, these estimated values remain useful to adjust the flavor profile. The difference can be remarkable, but does not invalidate the creative process or sensory appreciation.
Therefore, the next time you design a recipe or compare values, remember that the figures are a reference rather than an absolute. True magic is to know how to balance ingredients, techniques and your palate to create memorable beers, regardless of the number on the label.
