Craft enthusiasts enjoy exploring the depths of pints uncharted, but they don't sail without navigational equipment. One of the most ubiquitous and least comprehensible methods of navigating the heavy seas is the IBU scale.

The rate of bittering is an important influence on taste as the success in the marketplace of the Dogfish Head brand's 60 Minute IPA and 90 Minute IPA has demonstrated. But an IBU scale is more accurate for measuring bitterness than any method based on the rate of hops addition.

IBU is an abbreviation for the International Bitterness Units scale, a gauge of beer's bitterness. What IBUs measure are the parts per million of isohumulone found in a beer.

Isohumulone is the acid found in hops that gives beer its bitter bite. Though the IBU scale can be used as a general guideline for taste, with lower IBUs corresponding to less bitterness and vice versa, it's important to note that malt and other flavors can mask the taste of bitterness in beer.

Therefore, a beer with 20 IBUs and a minimal malt character may have significantly more bitter taste than a beer with 60 IBUs and a powerful malt profile.

This has led to some debate amongst the craft community about how useful the IBU scale really is. IBUs aren't always reliable indicators of how beer tastes, depending on the style and ingredients. And the scale itself doesn’t account for a variety of factors that affect the actual taste of bitterness in a brew.

As a Gravity/Hops Ratio chart shows, the more malt that is used in brewing, the higher the gravity will be, or the amount of fermentable sugar in the brew. The higher the gravity, the more hop bitterness will be masked. Also, no two brewing setups are the same, meaning the utilization, or rate at which flavor and bittering elements of hops dissolve into beer is never the same.

Other variables include hop varietals used, the age of the hops, and length of time boiled.

The IBU scale also fails to take into account any other bittering agents – some malts, especially black malt can impart acidity, as can a slew of herbs and spices. In fact, before hops were incorporated into the brewing process, a combination of spice and herb known as gruit was the only way achieve the desired acerbic quality.

Unabbreviated and unexplained, IBUs are little more than a number for the consumer to sink their teeth into. And in the hop-centric American market, bigger and bolder are often equivocated with being better, making high IBU counts juicy pieces of fruit-- a built-in talking point for all parties.

The pursuit of hoppiness has created a literally bitter rivalry between breweries.

Flying Monkeys Brewery of Ontario currently leads the pack with “Alpha Fornication,” which clocks in at 2500 IBUs, blowing runner-up Mikkeller’s “Hop Juice X 2007 IBU” out of the water.

What none of these breweries explicitly state is that the human palate can only distinguish up to around 110 IBUs before it tucks into its shell and retreats down the esophagus.

It could be argued that IBUs have become as much a marketing ploy as a tool for understanding beer. So if IBUs aren’t entirely useful to the common drinker, is there a better scale?

“I do think IBUs can be overstated, and therefore can be misleading to the consumer” said Kevin McNerney, head brewer at 5 Seasons Brewing in Atlanta.

McNerney suggests an accompanying scale to define hop aroma, but in the end, “What’s in the bottle is most important.”

John Isenhour, Associate Professor of Brewing Science at Kennesaw State University, agrees that the best way to measure a beer’s qualities are with the five senses.

“With taste preferences and abilities all over the map, I'm not sure that IBUs in the current state of craft brewing tells the consumer an awful lot. My advice: just try a sample at the right temperature.”

To the brewer, beer is art, and art cannot be quantified. Treat IBUs like an art critique: a resource for insight and appreciation. But take them with a grain of salt. After all, beauty is in the eye of the beer-holder.