Bitterness is an attribute that can divide beer drinkers—some like theirs with bite, while others prefer a smoother drinking experience.
Often, when a consumer tries a beer for the first time, they might use the beer style to help them choose one that’s likely to have the level of bitterness they prefer. If they don’t like it, maybe they’ll order something else.
Brewers, however, need to be able to estimate and measure bitterness in a more accurate way. It’s not easy to quantify in a way that translates directly to flavor, but having that number helps in developing new recipes, ensuring consistency among batches, and—if brewing to style—ensuring that the beer fits guidelines. For example, most brewers wouldn’t want to release a helles that exhibits bitterness equivalent to that found in a West Coast double IPA.
Besides having a calculated estimate as a target, being able to measure bitterness can help you determine whether your beer is true to brand or whether something went wrong during the brewing process.
A Primer on IBUs
In the brewing industry, the standard scale for measuring bitterness is international bitterness units (IBUs)—sometimes known in Europe as European bitterness units (EBUs).
Put very simply, IBUs are a measure of the amount of isomerized alpha acids—the most important bittering compounds in beer—present in a beer sample. That allows brewers to quantify a sensory attribute that would otherwise be considered subjective.
Now, let’s take a more detailed look at how that bitterness gets into beer.
As brewers generally know, the bitterness contributed by different hop varieties is based on their alpha-acid content. Alpha acids are the main compounds that contain the bitter attributes of a hop cone or pellet. These are represented as a percentage, with higher percentages representing a greater quantity of bittering compounds present.
To extract the bitterness from the alpha-acid compounds, they need to be isomerized into iso-alpha acids. For hops, that happens under conditions of heat—especially boiling wort. Of course, brewers adjust their recipes to decide when to add which hops to the boil and in what quantities, keeping the expected bitterness in mind. Adding hops earlier allows for more boiling time and thus greater isomerization. Later additions get less isomerization time, so they contribute less bitterness (but more flavor and aroma). Dry hopping, because it occurs on the “cold side” during and after fermentation, doesn’t involve any isomerization.
(However, dry hopping can either increase or decrease our perception of bitterness in a beer—for example, by extracting polyphenols or raising the pH. That’s one reason bitterness is technically tricky to measure.)
Bitterness can vary greatly in a beer, but our palates can perceive only so much of it. Lighter lagers might go as low as 10 IBUs, while bigger West Coast or American-style IPAs might range from 60 to 120 IBUs. However, the human body can realistically perceive bitterness only up to about 100 IBUs. Anything more essentially tastes the same to us.
Testing for IBUs
Now that we’ve outlined some of the technical basics, let’s dive further into how brewers obtain this value.
The ability to analyze IBUs in-house is mostly limited to larger breweries—that’s because of the higher-level equipment and the chemicals needed to run the test. Smaller breweries without advanced labs can outsource this test, while those big enough to invest in the equipment still need to follow certain precautions. (For more on outfitting your lab, see Starting Up and Sizing Up Your Brewery’s Own Lab.)
The most common way to test for IBUs involves an iso-octane extraction. This method pulls the alpha acids out of the beer sample and into an isolated layer, which can then be measured as absorbance with a spectrophotometer (which is the piece of equipment that tends to have a hefty price tag). Most units measure in the visible spectrum, but IBU testing is done in the UV spectrum, so it’s important to make sure the correct bulbs are included in the unit.
The other main aspect of this test is the chemicals needed. Hydrochloric acid and iso-octane are not standard chemicals for brewing operations, but you can order these from a science-supply provider. It’s critical to ensure proper ventilation when preparing solutions, to protect the tester from hazardous fumes.
The final safety consideration is related to waste disposal. When combined, these chemicals are toxic to water systems, so dumping them down the drain is not an option. Contact a local chemical waste–disposal company before beginning testing.
To get started with IBU testing, there are a couple smaller pieces of equipment to round out the necessary items. After mixing the beer sample with the chemicals, you’ll need a benchtop shaker to properly combine the layers into an emulsion. After that, you’ll need a centrifuge to separate the layers out again.
After that step, the alpha acids are present in the top, clear layer of the sample, which can then be tested for absorbance at 275 nanometers (nm).
Then, there is a specific calculation to translate the absorbance into an IBU value:
IBUs = 50 × (absorbance value at 275 nm)
You can easily add that equation to a spreadsheet, entering the absorbance to get the IBU value. That’s also the best method for properly collecting and retaining your IBU data.
It’s best to measure IBUs once fermentation is complete. Measuring mid-fermentation can result in skewed values because of haze and particulates. However, the best results will come from the brite tank or packaged product. The homogeneity of the samples from those two points will offer the most representative number.
Are IBUs Unfashionable?
IBUs were once important enough to craft beer that many breweries proudly displayed those numbers on cans and bottles. To some degree, they fell out of favor with the rise of hazy IPAs, in which bitterness takes a back seat to aroma, flavor, and visuals.
In a technical sense, hop additions also have moved later and later into the boil and whirlpool, with less isomerization of large hop loads. Breweries still test for IBUs, but they’ve arguably become less predictive of how we perceive bitterness.
The most important reason to measure IBUs is to ensure consistency among batches. It’s worth noting that measured IBUs from testing are not the same as the calculated IBUs based on a recipe. For the sake of consistency, it’s better to have benchmarks based on finished product rather than to rely only on estimates.
It’s also common for the bitterness of certain brands to slowly change over time—IBU drift. If you aren’t measuring and tracking that data, you’ll have no way of knowing how far off your bitterness is from your original recipe.
There’s always the argument that as long as it tastes good, the beer is fine for release—despite minor changes in bitterness over time. However, those drifts could also be costing the brewery money in unnecessarily expensive hop additions. Being able to track IBUs and calculate an exact level of bitterness can help the brewery save money by not adding more hops than are needed to hit the target.
That applies especially to higher-IBU beers: If those levels are approaching 100 IBUs, adding more for bitterness won’t have an impact on human sensory. Anything above that is probably a waste.
Even if a brewery can’t measure the IBUs on every batch, it’s important to get baselines when scaling up a recipe or implementing new brewhouse equipment. Both cases can result in different efficiencies and thus different levels of bitterness as a result of the boiling process. Testing IBUs on early batches will ensure that a brand has the same level of bitterness at multiple facilities.
Measuring bitterness in beer might seem old-fashioned or redundant in a world of hazy IPAs, but being armed with the data will help you better understand your beers and your brewhouse. You can use this data to track and adjust for changes in hop varieties as well as make sure that IBUs are consistent among batches.
Overall, this is just one more factor that ensures the beer is consistent for the consumer to experience time and time again.