Everything to know about IBUs and the IBU scale.

The International Bitterness Units or IBU is one way to measure how a beer tastes in terms of bitterness. While the bitterness of beer plays a significant role in a flavor profile, it is only one of many factors. Alcohol content, malt and water quality, yeast fermentation byproducts, bacteria, and aeration also affect a particular beer's taste profile.

Furthermore, an IBU rating alone does not indicate a good or bad tasting beer. For example, a super low IBU on an American Pale Ale could be just as great as a pale ale on the other end of the spectrum. It is really a matter of personal preference with some people enjoying crisper flavors and others enjoying milder flavors.

What are IBUs?

An IBU (International Bitterness Units) is a chemical measurement of isohumulone in a beer. This is the measurable byproduct of heating hops during the brewing process. Hops come in many varieties and play different roles in different types of beer. But they contain alpha acids, which are bittering compounds extracted during brewing.

Among the many qualities that affect a beer's taste, bitterness is one that human taste buds seem to be particularly sensitive to. Rather than focusing on a high IBU (strong bitterness) or a low IBU (mild bitterness), brewers focus on balancing the taste profile.

Unfortunately, there is plenty of room for debate when it comes to what makes a balanced flavor. Individual perception of mouthfeel, flavor, and aroma is a personal preference.

Decreasing International Bittering Units alone can make a beer taste smoother by merely lowering the bitterness. But beers with high IBU counts can also taste smooth by balancing them with high residual sugars or strong fruit flavors. Similarly, low IBU beers can have a perceivable bitter taste, especially if they are heavy in grains or coffee flavors.

History of IBUs

People have been brewing beer in one form or another since biblical times. Ancient brewing recipes often incorporated herbs and spices to flavor the beer, while more modern recipes rely largely on hops. Beer brewed with hops has a wonderful variety of flavor and a longer shelf life than other brewing methods.

Brewers have been using different varieties of hops to brew beers for around 200 years. Hops or the flowering part of the hop plant is used primarily for brewing beer and herbal medicines. When brewing beer, the different varieties impart different flavors like floral, fruity, or citrus notes onto the brew. Besides adding flavor, the hops contain a high amount of alpha acids that break down into bittering agents during the fermentation process.

It is not an exact science, and many variables can change the way a beer tastes, but generally speaking - more hops means a stronger bitter flavor. Different varieties of hops also contain different alpha acids levels, with some being used primarily for bittering and others primarily for flavor or aroma.

How Hops Help When Brewing Beer

Hops are most commonly associated with adding bitterness to a beer. But the hop flower actually contains two parts, the hop, which requires boiling to extract the acids. And, essential oil, which boils off easily. This means there are different hops for different purposes.

Hops have alpha acids, which are the most common bittering compound. They also contain beta acids, which contribute antimicrobial properties to the brew and essential oils that add aroma and flavor.

Hops are most often dried and boiled. However, dry hopping and fresh hopping have emerged as ways to alter the beer's flavor with floral, citrus, and fruity accents without affecting the bitterness. The hops plant's choice, stage of brewing, length of exposure, and quantity can change the impact that the hops will have on the final product.

In the United States, the most common hops are Brewer's Gold, Cascade, Chinook, and Citra. Many brewers actually use a blend of different hops in order to achieve a unique flavor profile. Brewers Gold has a fruity and spicy aroma similar to black currants. Cascade hops are known for their flowery and citrus notes like grapefruit. It is also the most widely used dual-purpose hop in the United States, used for both bitterness and aroma. Chinook is spicy and piney, whereas Citra has some apricot, peach, and other tropical aromas and flavors.

The vast majority of hops production goes to the beer brewing industry, but you will also find these plants in medicinal and cosmetic applications. Hops appear as ingredients in anti-inflammatories and sedatives and are used in herbal teas and sleep aids.

The benefits of adding hops to beer brews are long. The beta acids in hops impart antimicrobial and preservative properties onto the beer and help clarify the wort, giving the brew a good color. Hops also allow the finished beer to have a good head and allow breweries to store and ship their products while maintaining stable, consistent flavor.

What is the IBU Scale?

When referring to the strength of a beer, we commonly use two different terms with different meanings. You are likely more familiar with Alcohol by Volume or ABV, which is a measure of the beverage's alcohol content and an indication of its strength as it relates to impairment.

IBU is a lesser-known, but just as important measurement. A beer connoisseur is probably more concerned with International Bittering Units as it is a measure of the bitterness or strength of taste (read: enjoyability) of the beer.

IBUs are measured on a scale that starts at zero, representing no bitterness. While the scale technically has no limit for the most bitterness, there is a point where you can no longer keep a balanced flavor. The high end of the range that we tend to see from most commercial brewers is around 120.

How do you Measure IBUs?

Calculating IBU looks like a one part science experiment, fully staged with beakers and spectrophotometers and a one-part math equation, at least when the professionals do it. In short, beer mixes with hydrochloric acid to produce iso-octane. Isomerized alpha acids (Iso-alpha acids) are extracted, then measured by the spectrophotometer which judges the absorbance of light that passed through the beer/acid mixture at a specific wavelength, in this case, 275 nm.

Measuring bitterness is a big part of quality control in a commercial brewing process, so the calculations must be precise. Homebrewers can get away with a rough calculation using the pre-boil volume, hops, and boil time (which affects hop utilization). There are a number of plugs and play calculators available online that can help you figure out the IBU of homebrew.

How do IBUs Affect the Taste?

We have mentioned a few times that IBUs are only one component of the taste profile of a beer. If IBUs are a measure of the bitterness, it is important to note that there is a distinct difference between measured IBUs and perceived (tasted) bitterness.

Most American light lagers have low IBU levels with higher malt brews increasing in the IBU level. India Pale Ales sit firmly on the higher end of the range with some of the highest IBU levels.

Higher malt beverages need to have a strong flavor profile balanced out by adding more hops, which in turn increases the bitterness. Similarly, IPA's are naturally hoppy and flavorful, and with the strong presence of hops comes more bitterness.

Isn't Bitterness in Beer Bad?

There are two camps when it comes to bitter beer - those who love it and those who hate it. Bitterness is one of the easiest tastes to perceive, and we come with a natural aversion to it built into our DNA thanks to years of instinctual hunter and gatherer behavior. But modern times have removed our instinctual need to avoid bitter flavors and allowed us to expand our horizons.

Some of us have found that we can actually develop a taste for bitter flavors. Think about how many people indulge in a cup of strong coffee as a daily habit. As craft brewers have experimented with hundreds of beer styles and different varieties of hops - those of us who enjoy a good citra-hopped Double IPA or Imperial Stout have been re-conditioning our brains to enjoy the hoppiness. There is even a subculture of craft beer enthusiasts that call themselves hopheads. They are more than just a group that enjoys the bitter punch of a hoppy beer; they thrive on it.

We are in the low IBU blonde ale camp.

The Takeaway on IBUs

Craft beer brewing has enjoyed a resurgence in the last fifty years. Small breweries, along with individual brewers, have taken up the hobby, steering the direction of craft brewing. Modern styles of craft beers gravitate towards robust flavors and hoppiness or the bright, crisp, and bitter taste that a brew presents and finishes with.

The measure of a good beer is subjective, but certain qualities can help. IBUs refers to the taste of the bitterness of the beer. ABV refers to the alcohol content of the beer. And SRM refers to the coloring of the beer. All of these measurements are important in their own rights. As humans, we use input from all of our senses for a combined drink experience. This includes the color and aroma as much as the taste and alcohol content.

Trends between American and European brews vary widely; each culture likes and dislikes certain things. While beer drinkers and craft brewers around the world are seemingly preoccupied with measuring, calculating, and comparing IBUs as a measure of a good beer, but at the end of the day, it is all about perception, likes, and dislikes.

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