Geek Speak Decoded: IBUs, Hops, and Bitterness

This is the first in a series of articles on technical topics that might be of interest to the average craft beer consumer. They will cover topics that are on the minds of brewers when they design brews, but will be fairly non-technical and give only the essentials to help our readers better understand and appreciate the beer they drink, and decode any craft beer marketing material that they might come across.

By now, anyone who’s been to a respectable beer bar and tried to order an IPA has surely heard of IBUs, and might even be aware of a link between this number (a measurement of bitterness) and how much hops the brewer used. But there’s much more to consider here that gets lost on most drinkers.

Indulge me for a second with a geeky analogy from another realm. The situation with IBUs reminds me of a similar one a few years ago in the chip wars between Intel and AMD. Chips used to be marketed by their clockspeed in GHz. This gave the consumer a nice, simple way to compare the performance of two chips or the PCs running them without having to be a computer engineer or understand the underlying architectures. It was a very convenient tool for consumers and was widely exploited by manufacturers.

The problem was that the number by itself was useless; Intel figured out how to increase their chip’s clock speed by doing less work per clock tick (and thereby generating less heat and allowing them to run “quicker”). The result was that an AMD chip had better technology and would outperform an Intel chip with the same GHz number on it. But they were also more expensive and because the numbers were the same, consumers would pick the cheaper Intel chip, never fully understanding the real issues affecting performance. This led to a really ugly situation where AMD started using their own proprietary (and subjective) numbering schemes that didn’t really allow the consumer to casually compare performance at all. Thus the irresponsible use of this number as a marketing tool rendered it utterly useless to consumers. I fear the same thing might be starting to taking place as we speak in the crowded world of IPAs and other highly hopped beers.

IBU stands for International Bittering Unit, and is a measure of how much hop bitterness is present in a beer. The craft beer market in the US caters to a rebellious lot of consumers that are shunning the characteristics of mass-produced fizzy yellow lagers, particularly by actively seeking intensely flavored and highly hopped beers. The IBU has become the latest tool in the craft beer marketer’s kit, letting drinkers see at a glance which IPA is most intense and hoppy, and therefore better… but this number alone can’t tell you that, and it’s important for consumers to understand why.

First, one pivotal key to brewing a good beer is balance. An intensely hopped, bitter IPA is not going to taste right if this bitterness is not balanced by malty sweetness. There’s a simple rule of thumb for calculating how balanced a beer is, using a value known as the BU/GU ratio, which I will cover more completely in a later article. Essentially it is Bittering Units (IBUs) divided by Gravity Units, which is a measure of how much residual sugar is left dissolved in the beer after fermentation, the rest having been converted to alcohol. (Brewers typically use the original gravity, i.e. before fermentation takes place, in the BU/GU calculation, but it is still a decent proxy for the residual sweetness since attenuation-the portion of available sugar fermented-of most yeast strains typcially doesn’t vary enough to throw off the results.)

Even understanding this simple ratio does little to help the consumer, however, as the gravity figures are not touted as frequently as the IBUs. Even if you used alcohol content as a proxy for original gravity (which is feasible but troublesome for the same reason OG doesn’t correspond perfectly to residual sweetness), there are many other factors that can affect the percieved balance of a beer.

The second issue with the IBU rating has to do with the chemical reactions that take place during the boil. Hops contain many chemical compounds that affect the character of beer, but for our purposes we’ll focus on two groups: alpha acids and hop oil compounds. As the hops stew in the boiling wort, two things happen: alpha acids undergo a chemical reaction known as isomerization, which produces the bitterness that hops are known for. The other is that the volatile compounds in hop oils, which provide a rich tapestry of flavor and aroma to the finished beer, are slowly boiled away and lost forever. Therefore, hops that are added near the end of the boil (or even after the boil in a hopback or during conditioning in a process called dry hopping) will impart more flavor and aroma to the brew since the compounds don’t boil off, but will add much less in the way of bitterness (i.e. lower IBUs).

So what does it all mean? Higher IBUs do not indicate a better beer, by any stretch of the imagination. They measure bitterness, but say nothing about balance. Furthermore, bitterness comes from hops, but unscrupulous brewers can goose their IBU numbers and attract more attention by boiling all of the delicate hop oil flavor out of their hops to extract the maximum bitterness. Just be aware of this the next time you belly up to the bar for an IPA and are greeted by the “convenience” of having IBU numbers in front of you. Judge beers by taste, not by numbers.


What Harpoon Brewery Can Teach Us About Yeast

One thing about Harpoon has confused me ever since I started brewing for myself: their insistence on using a single strain of yeast for all of their main lineup of beers. It is a rather broad lineup, representing major American, British, and German styles, and now with the addition of UFO White, even a token Belgian. Despite their use of Ale Yeast, they field a respectable lineup of Lager styles, including Octoberfest (fall seasonal), Kolsch (summer seasonal), and Munich Dark (my personal favorite from their main lineup, available year round at the brewery but unfortunately rare elsewhere). How is this possible? Why don’t they seem to succumb to the limitations presented by a single strain of yeast?

Asked about it during the tour I attended, the guide simply explained that flavor differences among the styles were a result of ingredients, that is the barley and hops were different, but that the common string running through the beers in their main lineup-marking them like a signature for anyone with a palate refined enough to read it-was the fruity profile of their proprietary yeast strain. This didn’t quite do it for me, so I decided to dig a little deeper.

First, a tiny primer on yeast for the uninformed. Yeast are single-celled organisms that turn sweet wort into beer. They breed, then they feed, then they sleep until someone provides them more food (not a bad life if you ask me). During the feeding process, they turn simple sugars in wort into alcohol and carbon dioxide (which if trapped, as in bottle conditioned or cask beer, will naturally carbonate the beer). They also produce various other compounds that impact the flavor and aromatic character of the finished beer, among them esters (a class of compounds with fruity or citrusy flavor and aroma) and phenolics (a class of compounds with a spicy flavor and aroma).

What the tour guide was saying then, is that Harpoon selected and then patented their particular strain of yeast based primarily on the fact that the founders were particularly pleased with the estery profile it produced. The strain is also an ale yeast, which works quicker and is, by most accounts, less temperamental than lager strains (we’ll get into the difference in a later article). They must have worked very hard to find just the right strain, and I imagine that using a single strain is very convenient, in that it limits the chance of cross contamination within the brewery and makes the work of managing the yeast farm that much simpler. But how do they get away with it?

Lets break this down by style. I’ll be referencing the BJCP style guidelines alot for this; for those unfamiliar, this is the body responsible for certifying people to judge beer competitions (also not a bad life), and they are also the clearing house for style definitions in a way, so that all us beer geeks around the world can use a consistent vocabulary when discussing matters of style.

First the ales in the British and American tradition, as there is some overlap here. Harpoon brews an IPA, a combination Pale Ale/Amber Ale, a Brown Ale, and an Irish Red Ale in the Spring. American and British strains of ale yeast do tend to have somewhat similar, estery profiles, so it’s not surprising that the descriptions for nearly all of these styles make a mention of fruitiness or esters in both aroma and flavor.

The only exception is Irish Red, which is expected to contain no esters according to BJCP. However, there is nothing that says you can’t use an estery yeast to make a beer with a clean, ester-free profile. You can think of yeast profiles somewhat like a stereo with a broken tuning knob. You can turn the volume up and down (by playing with fermentation temperatures or pitching rates…more on this in another article), but there’s not much you can do if it’s tuned to the wrong station. Besides this, it’s possible that you can even make a fine Irish Red with a fruity, estery profile as well, it just wouldn’t fit into the defined style category very well.

When I started to consider the German styles in the lineup things got a little hairier, though. The Summer Beer (Kolsch) is no problem; BJCP describes it as a “Hybrid” beer made with a clean ale yeast. This is geek-speak for a beer made from ale yeast, working at very low temperatures to create a relatively clean profile (having less esters than the yeast would otherwise make) and then lagered to further round out the edges in the profile (lagering roughly corresponds to those conditioning tanks in the brewery, near which the air temperature drops a few dozen degrees!). The description also refers to some fruitiness in flavor and aroma, originating from fermentation; this is our good friend the ester at work, just with less potency than the British and American ales, brought about by a low fermentation temperature.

The German lager styles were a bit more troubling for me; that would include Munich Dark (or “Dunkels”) and the Octoberfest fall seasonal. Lagers ferment at temperatures much too low for ale yeast, resulting in a remarkably clean profile. This is why all the fizzy yellow American stuff is lager beer (though not particularly good examples of it…ask a German). It is possible to produce a lager beer with ale yeast, if you have a particularly clean, versatile yeast that can keep working at low temperatures and produce a fairly clean fermentation. When we taste the Harpoon lineup with this in mind this is pretty much what we find, fairly clean tasting beers that are probably just a tad more estery than some other examples brewed with lager yeasts; but honestly the extra complexity is not unwelcome for folks who live outside style boundaries.

This is good enough for Munich Dark; Dunkels are generally a clean but roasty lager (my intuition being borne out by BJCP, which says there should be no fruity esters or diacetal in Dunkels). But I’ve always known the Octoberfest/Marzen style to have a sort of unique spiciness to it, which I always attributed to the yeast (that is, from our old friends, the phenols). I checked the Wyeast and White Labs sites for their respective Octoberfest strain descriptions, and was surprised to find that neither made any mention of spiciness or phenols, focusing instead on the complex maltiness of the finished beer. A little further digging turned up that in fact, the spicy flavor I’ve found in other ‘fest beers probably came from the German “noble hops” so often used in these styles, rather than from the yeast profile. This example illustrates an important point that we’ll keep coming back to in later articles, that the brewer has many levers at their disposal to effect the flavor and aroma characteristics of the finished beer.

So far so good. All of the beers in the Harpoon lineup either have a fruity profile according to BJCP, or are fairly clean, both of which are achievable with an estery yeast. Winter Warmer (the winter seasonal) is a spiced beer, which can be of any style, so it’s not really covered by BJCP in any detail and we can ignore that one. The bulk of the flavor profile is most likely from the spices used, rather than the yeast. This just leaves the elephant in the room.

The Punks have a well known prejudice against the UFO beers. We are fans of Harpoon, and it has always caused us some inner conflict that some of their most commercially successful offerings are so unpalatable to us. It’s not that they’re bad beers, but something is amiss here as far as we are concerned, and the answer lies in the yeast.

The UFO series is Harpoon’s line of unfiltered wheat beers. It all started with the UFO Hefeweizen, which is a style with German roots. Then they added raspberry to it (we feel too much raspberry…ever crammed raspberries up your nose?) to make Raspberry UFO. Then recently they added UFO White, which is based on the Belgian White Ale (or Witbier) style of unfiltered wheat beer; this is our favorite from the series but still doesn’t quite make the cut for us. We’ll also lump in the new Crystal Wheat (or “Kristallweizen”) that has started showing up in summer mix packs as a limited edition brew, because as far as we can tell this is the filtered version of the original UFO, with some lemon peel for spicing.

The problem here, for us Punks, is that the base styles of these beers (which we love with a passion) use very specialized (and often temperamental) yeast strains. The German Hefeweizens use weizen yeast strains which produce a very complex profile rich in banana-like esters and clove-like phenols. The Belgian yeast used to produce traditional Witbiers, too, is known for a profile dominated by spicy phenols, at least according to the strain descriptions on Wyeast and White Labs sites. But the Harpoon yeast doesn’t have a significant phenol profile to speak of; it was selected specifically for its estery profile. So why would you use it in beer styles known for phenolic character?

What we have here isn’t an example of bad beer, or even beer brewed out of style, but an example of the Americanization of old world styles. One can now speak of an American Hefeweizen style that uses simple American ale yeast but lacks the complex clove and banana flavor of traditional German Hefeweizens like Punk favorites Ayinger, Erdinger, or Schneider; they tend more toward citrusy flavors (we’ve been known to describe UFO as tasting like you are sucking on a lemon…this is an exaggeration, but only slightly when compared to more traditional Hefeweizens). Likewise many American breweries are making what they refer to as White Ale by using typical American Ale yeast and getting the “phenolic” character by simply adding spices like coriander to the beer. The result is somewhat less than satisfying once you’ve had the real thing.

This doesn’t necessarily make UFO, or other Americanized beers for that matter, a bad beer. I wouldn’t dare be so unpatriotic so soon after our most hallowed national holiday. Sometimes we get it very right. I can’t think of a single English IPA that I’ve ever tried, even though the style originated there. It was originally brewed heavy and hoppy to survive the long journey to the military outposts in India, but I feel that it finally got its sea legs right here in the US during the craft beer revolution of the eighties and nineties (by the way, Harpoon makes one of our favorite examples of this style). But occasionally, when the base style is so defined by the yeast that makes it, why accept substitutes? This is why the UFO series will never really receive a passing grade from the Punks. It is a fine beer if you like these Americanized styles, and I encourage you to try it and form your own opinion. Just make sure to reach a bit deeper into the cooler and try it alongside one of the more traditional examples of the style I’ve listed above, otherwise you are doing yourself a great disservice. Harpoon brews a fine American Hefe – citrusy, crisp, and refreshing, it makes a decent alternative to your typical lawnmower beer – but intercontinental it is not.

One feels that even Harpoon brewers themselves are fully aware of the limitations presented by their one-yeast rule. This is no doubt why their specialty beer lineups, including the Leviathin series and Punk fave 100 Barrel series, have ditched the limitations and produced some very fine, unique beers in the process. But I must say, supported by the BJCP guidelines as well as my own palate, that they’ve done an excellent job of selecting styles that are appropriate for their chosen strain, even when those styles don’t match my particular palate.