Hop University - Day 2

OK homebrewers and the brave few who have made it to day 2.  Hop history is down, on to the fun stuff, how hops are used in beer making.  We’ve discussed that hops offer bitterness to beer which balances the sweet malt.  In order to get the bitterness out of the hops, they must first be boiled in the beer (wort).  The boiling causes the hop oils to isomerize and become soluble in the beer.  The hop oils contain two types of acids, Alpha acids and Beta acids.  Alpha acids provide the bittering component.  The Beta acids do not isomerize in the boil making them insoluble and provide only hop aroma to the beer.

Hops are typically rated based on their Alpha acid percentage by weight.  This rating gives the brewer a guideline for how much bitterness can be expected from a particular hop.  For example, a Cascade hop is around 4.5 Alpha acid % and a Galena hop is around 12.5 Alpha acid %.  So the brewer will need to use a lot less of the Galena hop at 12.5 AA% then they would Cascade at 4.5 AA% hop to get the same amount of bitterness.  Brewers measure the amount of expected bitterness for their beers with IBUs (International Bitterness Units).  The higher the IBUs, the higher the expected bitterness in the final beer.  Below are some typical values for certain styles of beer.

Light Lager (Bud Light, etc) – 5-10 IBU

Dry Stout (Guinness) – 30-45 IBU

American Pale Ale (Sierra Nevada) – 30-45 IBU

American IPA (Founder’s Centennial) – 40-60 IBU

Double IPA (Stone Ruination) - 60-120 IBU

Generally speaking the higher the IBU the more bitter the beer will be.  Although the Dry Stout and the American Pale Ale have the same IBUs, the stout has sweet malts which will balance the bitterness.  So even though they could have the same IBU, the stout will seem less bitter because of its sweeter malt components.

Now that we know how hops provide bitterness to beer, we need to figure out what is it going to taste like.  There are two types of Alpha acids, Humulone and Cohumulone.  Humulone is thought to provide the softer more desirable bitterness.  Cohumulone in contrast is thought to be harsher in its bitterness and therefore less desirable.  The next consideration is the four main essential oils in hops which contribute to flavor.  They are Myrcene, Humulene, Caryophyllene, and Farnesene .  The two oils that brewers are concerned with (at least I only worry about the two) are Myrcene and Humulene.  Myrcene lends a more citrusy and tropical note to the beer while Humulene has a more spicy and floral signature.   With information regarding the Cohumulone levels and the amounts of the essential oils in particular hops, brewers can get a good idea of what hop characteristics they can expect from their finished brew.  Below are some examples of hop flavor characteristics for certain styles.

IPA – Bell’s Two Hearted – uses Centennial hops which are high in Myrcene causing big citrus and grapefruit character.

Pilsner – Pilsner Urquell  - Uses Saaz hops which are high in Humulene lending a mellow spice and floral note.

American Lager – Sam Adams Boston Lager – uses Hallertau which is high in Humulene making it spicy.  It is also low in Cohumulone so the bitter is more pleasant and less aggressive.

IPA – Bridgeport The Czarr – is brewed with Chinook hops which are high in Cohumulone and give it a very aggressive, harsh bitter character.

 References:

http://en.wikipedia.org/wiki/Hops

http://www.homebrewtalk.com/wiki/index.php/Adlupulone#Adlupulone

http://beeradvocate.com/forum/read/3808775