Craft Beer’s Bitter Pill – What’s The Value Of The IBU?

by Mark E. Lasbury for Indiana On Tap

Hops in beer are for flavoring and act as an antibacterial. And most craft beer fans also know that hops are an ingredient that can make beer bitter. Beers that are considered more bitter – pale ales and especially IPAs – tend to have higher levels of isomerized alpha acids from hops, but as with all things, there’s more to their bitterness than just boiling alot of hops.

Walter is a huge fan of beers with high levels of hop bitterness; Crooked Tree IPA from Dark Horse, Devil Dancer TIPA from Founders, and Grapefruit Jungle from Sun King are some of her favorites. She drinks IPAs more than any other type of beer, but a few years ago she started to ask questions about their descriptions. The hop bitterness she so craved, as supposedly reflected in the IBUs (International Bitterness Units), didn’t always agree with what she tasted.

Sure, some bitterness was there, but not every beer with a high IBU count was as bitter as she expected. Plus, there were other flavors coming out of the hops, not just bitterness. She was very happy when written descriptions started to include the hop varieties that were in the different beers; this allowed her to focus more on the holistic beer experience, including what flavors to expect beyond bitterness.

This is a great chart for describing what different hops contribute to beer. A poster sized version can be purchased at: Image credit: Hops: Bitterness, Flavours & Aromas

As she has learned, hoppy doesn’t just mean bitter. Different hop oils are also responsible for the aroma and flavors that individual hops display (see image at right). Myrcene tastes and smells citrusy, floral, or piney, while humulene is spicier and carophyllene has a different floral tone and tastes a bit earthier to me. Different varieties of hops, of which there more than 100 and growing – contain different profiles of these oils and therefore have different flavors and smells. Citra hops have the largest amount of myrcene, so they taste very fruity. Magnum hops have more humulene and less myrcene, so they are much spicier.

Hop oils are quite miscible in water and steam, so they are easily lost in the boil (see this post). Losing the oils from the hops means that the bitterness is the only major characteristic of the hops that will remain. This is why the timing of the hop addition is important- the longer the hops are boiled, the more flavor and aroma will be lost, while more of the alpha acids will be converted to the bitter iso-alpha acid form (more on this below).

To keep more of the oils, some beers are late hopped, with additions made just before the boil is completed; this increases flavor and aroma while adding little to bitterness. Other beers are dry hopped, with whole flower or pelleted hops added, usually after after fermentation. Dogfish Head introduced the world to continuous hopping with their 90 minute IPA, with dozens of hop additions throughout the boil. This process results in both massive  flavor and profound hop bitterness, about 90 IBUs worth.

So 90 IBUs is a lot, but what does that mean? In truth, the IBU was really an invention of the brewers themselves, designed to help them brew consistent beer from batch to batch. The IBU was never intended to imply anything to the person sitting at the rail tasting the beer. That might sound silly given how almost every brewery posts their IBUs for each beer right next to the ABV, but follow along and see if the explanation below makes sense.

In technical terms, an IBU is one milligram of iso-alpha acids (mostly iso-humolones) per liter of beer – basically it’s a parts/million measurement. To get to that number, formulas are involved. First of all, most home brewers don’t even use IBUs, they use descriptors like AAU (Alpha-Acid Units) or the equivalent HBU (Home Brewer Units). AAU/HBU is more a measurement of bitterness potential of beer, based on the alpha acid content of the particular hop variety. Similar to the situation with hop essential oils, each hop varietal has a particular amount of alpha acids in its flower. To calculate the AAU, the number of ounces of each hop variety in a batch is multiplied by the percentage of alpha acids in that hop (which are published) and then multiplied by 1.34 to convert the metric formula to the American standard, oz/gal.

OK, this looks like math, but it’s not so bad. The “AA%” is unique to each hop variety, and the “U” (utilization percentage) can be looked up in charts – but it will be affected on boil time and wort original gravity (how much sugar is in the wort). Image credit:

The AAU/HBU is a measure of hop bitterness potential since it doesn’t take into account things like the boil time, the rate at which the alpha acids are converted to iso-alpha acids, or the amount of malt in the beer. In general, if a home brewer likes a beer and wants to replicate its bitterness with a different hop profile, then this formula will tell them how much of that new hop or new group of hops will be needed.

On the other hand, commerical brewers usually uses the IBU. The IBUs in a beer can be determined mathematically by added a factor called hop utilization (often represented by a U) to the AAU formula. The hop utilization numbers are published for the various hops,  and describe what percentage of the alpha acid will be converted to iso-alpha acid during an average boil with a wort of average original gravity (amount of sugar available for fermentation). If original gravity is higher than normal, then utilization will be decreased by a couple of percentage points (no one I talked to knew why, but they all agreed it is true). And of the boil is longer than average, more of the acids will have time to be isomerized, so utilization will increase by a few percentage points. Because of this ambiguity in the formula, many large brewers use laboratory methods like iso-alpha acid extraction followed by spectrophotometry. Suffice it to say that they have more accurate IBU numbers.

Whew! That was a lot of science and math, but at least it has answered the question – more IBUs = more bitter, right? NO!…..there is such a thing as perceived bitterness. Walter describes hoppy beers as balanced (less bitter) or unbalanced (more bitter); other people refer to how hop forward a beer might be. This is because the IBU number alone tells the drinker very little.

A lot of the vagueness has to do with the sugar content of the beer. Take five IPAs for example – increasing the IBUs might increase the perceived bitterness in a general direction, but only maybe. I’m sure that at some time you have tried an IPA thinking that it will be very bitter only to find it is more balanced. What about a DIPA? It has twice the hops, but does it taste twice as bitter – not usually. Higher hops with higher malt levels will not be perceived as that bitter. So, many beers might be advertised as extremely high IBU, but that doesn’t mean they taste very hop bitter.

Heck, most beer judges agree that even if they can detect small changes in IBU at lower levels, most people can’t taste anything more than 100-120 IBU. Devil Dancer is said to have 200 IBU, and some beers go much higher, but it’s a distinction without a difference – the high malt levels reduce both actual and perceived bitterness, and people have an upper perception threshold far below the IBU levels of many commercial beers. Convinced yet about the futility of chasing IBUs?

Therefore, some people are moving toward a quantity called the bitterness unit:gravity unit ratio (BU:GU), including the BJCP (Beer Judge Certification Program) style guide. To obtain a BU:GU value, one takes the original gravity of the wort (for example 1.049), and multiplies the part to the right of the zeroes by 1000. This means that the example wort above would possess 49 gravity units. The IBU (for example 35) is then divided by the gravity units to give the BU:GU (0.714 for this example, typical of an APA). An APA with a BU:GU higher than this will probably taste more bitter than the average APA.

Click here to get a bigger view. This chart shows the BU:GU for most beer styles. For example, if you make a bitter barleywine, its will likely be an American version rather than an English, and should have a ratio of about 0.85 – more than that and you will be talking about a very “hoppy” barleywine. Image credit: Home Brew Manual

I say “probably” because other issues, like the amount of roast on the malt can also play a role. Strong flavors, like roast, or infused fruit purees in the fermenter or after can augment/hide much of the hop bitterness. Therefore, BU:GU is still just an estimate of perceived bitterness. Never mind that different people will taste the exact same beer differently.

Scott Ellis, head brewer at Big Lug Canteen, says that he uses the IBU calculation method to determine an IBU estimate for his beers but he is always aware that without using spectrophotometry or the even more expensive electrospray ionization mass spectroscopy, his IBU numbers are just that – an estimate. As far as he is concerned, IBUs tell you less about the beer than BU:GU might, but if it were up to him, Big Lug wouldn’t post any bitterness numbers. Skip DuVall and Dan Krzywicki at Chilly Water have gone just that direction. They agreed from the beginning of their venture together that they would not post IBUs for their beers. They both feel that that this measurement does little to inform the drinker and can actually harm a drinker’s experience by setting up false expectations.

So what conclusions can we draw about hop bitterness numbers? For Walter and I, they suggest that since IBU means more to a brewer making a beer than it does to a drinker consuming it, and since IBUs can be hidden in a high malt or flavored beer, then maybe breweries should stop posting the IBUs of their beers on Untappd and listing them as part of their beer lists and on their websites. The bitterness ratio (BU:GU) probably means more to us as drinkers, but I don’t know that many brewers have this information on hand since it means little to them as they make beer.

So this is our (Walter’s and my) new quest – get people to stop obsessing about IBU numbers and focus more on the flavors and characteristics of the beer. If you are the kind of person who needs a number, then start asking for the BU:GU as a slightly descriptive measurement of beer. However, since BU:GU is only meaningful if you know what the normal BU:GU is for every style – using this ratio will require more learning on your part.

Founders Devil Dancer is one of Walter’s favorite bitter beers, but not because the bottle says it has 200 IBUs. Image credit: Founders Brewing

So I’ve come up with an idea for all you drinkers who need a number to look at and compare – a brewery could calculate the BU:GU for each of its beers and then subtract the calculated ratio for their particular beer from the average BU:GU for that style as published by the Home Brew Manual. A negative number would indicate that this individual beer would tend to be less hop bitter than the average beer of that style, while a positive number would suggest a higher than average hop bitterness, ie. the more bitter it might taste to you. We could call it a Style-Specific Bitterness Ratio (SSBR). Hey, it might catch on – ZwanzigZ Craft Brewery (the 2016 GABF small brewery of the year) uses a “DOW” number for their barrel aged beers to let you know the “days on wood” for each beer – so why not an SSBR value too?

Of course, even this masterpiece of beer thinking doesn’t take into account things like roasted malts adding additional bitterness, fruit infusions masking bitterness, and higher attenuation (more sugar usage in fermentation) leading to less sweetness more hop bitterness in the final beer. So, SSBR will still be an estimate, just a more useful one.

On the other hand, perhaps the final solution to the bitterness conundrum is simple and math-free. We ask for a sample of a beer and decide for ourselves if it has an appropriate level of bitterness for our palate. Or even better, we could talk to our beer slinger or brewer about their beer and start a conversation. Some things are described better with words than with numbers.

  • EMonster Brewery

    “one takes the original gravity of the wort (for example 1.0049)” – 1.0049? Are they just brewing water?


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