What’s That Number? IBU and Measuring Bitterness


Like any craft beer drinker, you’re probably accustomed to seeing International Bitterness Units (IBU) posted on chalkboard menus and printed on cans and labels. American brewers love their hops, and American consumers love their amped-up IBUs, especially here on the West Coast. In fact, the craft beer market share of IPAs increased nearly tenfold since 2008, diversifying into subcategories like Session IPAs, Belgian IPAs, Imperial IPAs, and Black IPAs. Novice or cocksure drinkers often make the mistake of assuming that the higher the IBU, the better the beer or the more “intense” or bragworthy their choice will be considered. But there’s a lot more that goes into how bitterness and hoppy flavors are perceived, achieved, and explained.


Hops bring a lot of different elements into beer: a huge variety of flavors and aromas in addition to anti-bacterial properties and of course, bitterness. Everything depends greatly on how and when the hops are added during the brewing process. In order to gain bitterness, hops must be added early during the boiling process, where they undergo isomerization, a process that rearranges atoms within a molecule. In simple terms, the bitter alpha acid compounds are effectively dissolved into the wort, which they wouldn’t normally do in plain cool liquid. It takes a certain amount of time exposed to high heat to achieve this. Conversely, many of the other compounds responsible for flavor and aroma are heat-unstable, meaning that they are driven off with evaporation during the boil. Thus brewers typically add hops at different intervals to achieve a desirable balance of hop bitterness and hop flavor/aroma. Adding hops to an already fermented beer (dry-hopping) for instance, will not add any bitterness to a beer, but it will increase the hop flavor substantially. A dry-hopped, high IBU beer can seem more bitter overall.

So how do you measure real bitterness? One bitterness unit is equal to 1 milligram of isomerized alpha acid in 1 liter of beer. Brewers use calculators to know how and when to add hops for the right level of IBU in each recipe. But beer styles vary greatly–malt character and sweetness level depends on style. Stouts are roasty and dark, Pilsners are dry and light, ESBs are malty and somewhat sweet. Sweetness and other flavors serve to balance a hoppy, high IBU beer. Barley wine, for instance is usually 2-3 times as bitter as a Kolsch, but you may not notice due to the residual sweetness and rich malt flavors. Without a lot of IBUs, a barley wine would be cloying, syrupy, and unbalanced. Beer is truly a balancing act between flavors, just like many sauces and recipes.


Instead of adding more hops near the end of the boiling process (or as dry-hop additions), some breweries use hop oils or extracts designed to contribute only flavor and aroma in concentrate (although, depending on method, there are also products that offer isomerized hop acids, which will add to IBUs). This is attractive to brewers for a few reasons. A huge volume of hops is required by some recipes to achieve the ideal flavor and aroma, and that in itself can present some issues. Some wort is always lost: absorbed by hops or lost while removing excessive hop residue. Additionally, grassy or vegetal flavors can accompany a large hop addition. After all, hops are green plant material. Furthermore, many current hop extract products are extremely shelf-stable and won’t deteriorate into stale or skunky flavors down the road. Trappist-style beers (low IBU) and Imperial-style IPAs (high IBU) are common styles that might benefit from utilizing these “downstream” hop products. The oils and extracts can offer great control for making precise beers with better flavor.

IBU is merely one way to predict the overall flavor of a beer. Some breweries have adopted a more comprehensive way to determine the understanding of bitterness in beer called the BU:GU ratio. This compares bitterness units (IBU) to gravity units (in this case, a measure of sugars present in the original wort). Most styles end up with a range of 0.3-1, with larger numbers indicating a more bitter beer. Of course, this method doesn’t take into consideration the flavor of the malt itself nor the final gravity of the beer (which could be sweet or dry). So if you’re using the ratio, be sure to apply it in context with style in mind. And that’s just what I hope to underscore: context. No number used to measure beer will determine how delicious it is, how well-made it is, or how much you enjoy it.

Categories: What's That Number?

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