Beer and hops - popular American dry hop varieties

Close up of lupulin gold at the petal base of hop cones, where oils and resins are
encapsulated.  Photos by Charlie Papazian

It 's a century old tradition whereby most of the world's brewers focus on hop's bitterness quality.  Some bitterness is harsh, some more mellow.  Bitterness is measured by "Bitterness Units." 

• 0-10 is not generally perceived as bitterness in international light lagers and not at all perceived in other stronger flavored beers. 
• 12- 20 is a mild and pleasant bitterness in 4 to 5% pale, amber lagers and ales. 
• 20-30 units of bitterness will be perceived as mild and pleasant in more robust ales, stouts, porters, red ales and stronger lagers. 
• 40 to 50 units of bitterness will be assertive in most any type of lager or ale; especially intense in lower alcohol beers below 5.5.% and balanced for maltier stronge pale and India pale ales. 
• Beyond 50 BUs are reserved for hop emphasized beers.

Now that bittering units have been generalized, it's impossible to assess bitterness definitively when it comes to intensity.  Everyone has different thresholds of bitterness perception.  Also, the quality of the water, whether hard or soft, impacts the perception of bitterness dramatically.  Very sweet malty beers tend to mask the perception of bitterness. So that is why scientist have standardized bitterness by measuring a very specific chemical compound.  It has nothing to do with perceived bitterness.  So it goes.

Bitterness units are an actual measure of a compound derived from hops.  Bitterness units are NOT a measure of bitterness perception.  Hop bitterness 101 has now concluded.

While bitterness and its perception by the beer drinker is of primary importance, hop flavor and aroma are immensely influential overall character and balance.  Flavor and aroma are derived from hop oil compounds.  Bitterness is derived from hop resin compounds.  These are two different elements of hop chemistry.

American professional and homebrewing craft brewers have made hop flavor and aroma their mark and signature in brewing history.  Most of this science has yet to be researched.  Meanwhile perception experience guides most of craft brewers when it comes to choosing, using and blending hops for their aromatic and flavor contributions. 

2+2 does not equal 4.  The combination of more than two different hops does not necessarily result in an additive effect.  My experience indicates when certain flavors and aromas are combined, sometimes there is a synergetic effect resulting in a perceived unique aroma or flavor character, related but not necessarily indicative of the pure single hop characters. 

All of this gets very complicated with different fermentation temperatures (production and contribution of esters), water chemistry, malt character, choice of yeast strain and other factors.  The possiblities are endless and will never be completely catalogued.

Here are a two informational charts, the first of which is excerpted from the US Hop Growers Association presentation, "American Hops and Craft Beer in the United States." 

 Also see: Top ten hop varieties used by American craft brewers

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