Making Sense of Hops, IBU, and Bitter Beer

Since the onset of the IPA craze that we currently find ourselves in, bitter beers have been finding their way into pint glasses around the world. The term IPA (India Pale Ale) was originally used for beers that were shipped from England to India in the 18th and 19th centuries. The long shipping time required better methods of preservation, which hops are able to provide through the bitter compounds they impart upon a beer.

IBU is a measurement of the bitter compounds in a beer—in general, adding more hops to a beer results in higher IBU levels. While there are an endless variety of bitter beers with high IBUs, they all have one thing in common: hops, and lots of them! But, what does it really mean for a beer to be ‘hoppy’?

What are Hops?

Hops are the flowers of Humulus lupulus, known simply as the hop plant. As a member of the Cannabaceae family, it is closely related to cannabis, another aromatic plant grown for its flower buds. The earliest documented case of hop cultivation was around 750 A.D. By the 15th century, hops had made their way into beers around the world, although not without some conflict. Until then, gruit (a combination of bitter herbs) was the main flavoring agent used in beer—hops were considered a “wicked and pernicious weed” that threatened to change the beer-brewing landscape.

These fears quickly dissipated when brewers realized that hops provided strong antibacterial properties. The more hops they used in a beer, the longer it would last in storage—this was a good enough reason to make the transition to hopped beers. By the 18th century, hops had almost completely replaced gruit—and the brewing world hasn’t looked back since.

Germany and the United States have the highest hop production in the world, with each country having grown over 45,000 tonnes in 2020. The rest of the world’s hop production doesn’t even match one of these countries’ outputs (China, the next highest producer, put out just over 7,000 tonnes in 2020). Hallertau is Germany’s primary hop-growing region. In the United States, the Willamette and Yakima valleys of the Pacific Northwest support most of the production.

Hops and IBU: How Are They Related?

The International Bittering Unit (IBU) is a measure of the bitter compounds found in a beer. Most modern beers will display the IBU (along with ABV) to help consumers decide which beer might work for their palate. The scale technically has no upper limit, but an IBU above 100 is rare in commercial beers.

For example, the 90-Minute IPA from Dogfish Head is a popular Imperial IPA known for its highly-hopped flavor profile. With an IBU of 90, it provides a bitter drinking experience and is an acquired taste for the uninitiated. On the opposite end of the spectrum, Bud Light has an IBU of 6, which translates to a watery, flavor-less experience with no bitter sensations.

The alpha acids found in hops are the primary source of bitterness. Some hop strains have been cultivated to contain higher amounts of alpha acids, leading to their use as bittering hops. Varieties with low amounts of these bitter compounds—aroma hops—are added for their flavor.

Hops can be added at different stages of the brewing process, providing different effects to the resulting beers. Any hop variety can be used for bittering or aroma, depending on when they are added to the wort. While the brew is at a rolling boil, bittering hops are added to balance out any sweetness, and for the preservative effect. Aroma hops are added at the end of the boiling process, as too much steam can remove the fragile flavors found in the hop oils.

Popular Hop Varieties

Hops come in endless varieties, also referred to as cultivars. By selectively breeding hop plants to promote desirable characteristics, new cultivars are continuously created. As new styles come into the limelight—such as the recent explosion of IPAs in the craft beer market—certain hop varieties enjoy expanded cultivation and appreciation.

Each hop variety has a unique flavor profile, as well as traditional uses (either as a bittering or an aroma hop), though brewers love to experiment with new hops and methods.

Cascade Hops: Cascade hops were originally grown in America, but they are now cultivated worldwide due to their immense popularity. The variety is defined by its citrus flavor (sometimes narrowed down to ‘grapefruit’). It is also described as having floral and spiced aromas. When used as a bittering hop, it provides a moderate amount of bitter compounds.

Citra Hops: This hop variety was first developed and released in 2008. It was bred in the Yakima valley of Washington and was derived from Hallertauer, East Kent Goldings, and other hops. It is now one of the most widely-used hops in America, usually added to flavorful IPAs due to its citrus and floral flavors. Citra is a dual-purpose hop and is used as both a bittering and aroma hop.

Mosaic Hops: Mosaic hops have only been in widespread cultivation for about a decade, but they have quickly earned the respect of brewers around the country. This variety features a ‘mosaic’ of flavors, including notes of citrus, pine, grass, floral, earth, and berry. With a high level of alpha acids, Mosaic hops can be used for bittering, but the cultivar really shines when used for its complex aromas.

Magnum Hops: This variety was originally produced in Germany in the 1980s. Magnum hops are loaded with alpha acids, but contain little in the way of flavor—they are used almost exclusively as a bittering hop. The cultivar is known for high production value and large, heavy flower cones.

Amarillo Hops: This cultivar was discovered in the late 1990s (likely due to a mutation of a related variety, Liberty) and started receiving widespread use in the early 2000s. Amarillo hops feature floral, fruity flavors, leading to their nearly-exclusive use as an aroma hop. This variety is often thought of as a stronger version of Cascade hops. The Founder’s All Day IPA is a popular beer that utilizes the potent flavors of Amarillo Hops.