Hop Bitterness and an American IPA

As my first post of the new year I’ve decided to write a bit about hops, why they are bitter, how to get hop bitterness in beer, and how your taste buds (and nerve endings) perceive the bitterness. I’ll end by writing a recipe that I recently brewed for a really hoppy American IPA.

As we all know, the female cones from the plant species, Humulus lupulus, provide essential oils that when used in brewing impart a bitterness to the beer. Not only does this bitterness give beer a fresh and snappy taste, but it also acts as a preservative to bacteria that might otherwise spoil the beer. The oils found in the cones contain a wide variety of compounds that contribute to the taste and smell of beer.

The first that I will mention are the alpha acids humulone (left) and cohumulone (right) molecules. Both molecules will lend bitterness to beers, however there is a difference. Humulone parts a “softer” bitterness, while cohumulone is more harsh. This seems to hold true as the more mellow noble hops contain more humulone while American type hops (think Chinook) contain higher levels of cohumulone. Another alpha acid, adhumulone is present at very low levels and its contribution to bitterness is not well understood.

However, these molecules by themselves are not bitter. They have to go through a remarkable change in their molecular structure that is triggered by boiling wort. Check out the structures shown below to see what happens.

The triangle after the humulone molecule stands for heat and the molecules in parenthesis are the intermediates (what happens to the molecular bonds and atoms) during the reaction. In the intermediates, if you follow the arrows, you are actually following the movements of electrons. In the first intermediate, heat causes an electron to move from the OH on the top to the oxygen atom on the bottom left. In the second intermediate, the electron movements break the carbon chain (each carbon is represented by a corner of two lines) and flips it in the other direction. This “flipping” of the carbon bonds is called isomerization and hence you get isohumulone.

But why do we taste the bitterness of this molecule? Because type 2 taste receptors on the taste buds recognize isohumulone and sends signals to your brain telling you the taste is bitter. Interestingly, smell also plays a role and some of the same neurons are activated as you smell the hoppy liquid.

Hop oils also have beta acids such as lupulone, colupulone, and adlupulone. These acids do not contribute much bitterness since they readily percipitate out of solution in boiling wort.

As the story couldn’t get more complicated, there are other compounds that affect the flavor of the beer, with late hop additions adding plenty of these molecules. Mycrene for example, is found in many citrus fruits and provides citrus/tropical fruit aroma to american c-type hops. Amarillo can have up to 60% myrcene. Humulene can be found in high amounts in noble hops and lends the beer a spicy and herbal quality.

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So after going through the molecular structures of these compounds, how can a homebrewer select which hops and what is the best way to use them? The easiest (and most well-known) character is the % alpha acid. The higher the percentage, the higher bitterness your brew will have. What you may not know is the amount of all the other compounds that i’ve mentioned. However, there are some good resources that can give you a good ball park figure of the contents of each molecule for each hop. So for example, if I wanted to make a pale ale with soft bitterness, but without the herbal characters of noble hops I would choose a hop with low cohumulone levels.

What about using your hops to the utmost? Here are a few points to adhere to:

• When brewing a hop-centric beer, hop utilization is important for maximizing IBUs and the best way to attain that is to do a full wort boil.
• Keep your hop bill simple – brews that contain something like 7 different hops become muddled.
• If you want bitterness, add hops at the beginning of the boil. If you want hop flavor, add late in the boil (by the last ten minutes)
• Hop aroma is best achieved by dry-hopping and flame out additions.
• Fast cooling preserves hop aroma and flavor (less volatiles are released).
• The higher the gravity beer, the more hops are needed to balance the sweetness.
• MOST IMPORTANT: while some beers traditionally use specific hops, YOU are the brewer and use whatever you desire. Experimenting with different hops is also fun.

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Now that I have ranted enough on hops, time for a hop forward recipe. I brewed this recipe in early December hoping to submit it for competition this month New York City’s Homebrew Alley 5. The principle behind this brew is to make it very hoppy and highly attenuated similar to a west coast IPA. For this purpose, I decided to not use any crystal malts to maximize fermentability.

5 gallon recipe:

• 9.00 lb       Pale Ale Malt 2-Row (Briess) (3.5 SRM)
• 3.00 lb       Munich II (Weyermann) (8.5 SRM)
• 1.00 lb       Wheat, Flaked (1.6 SRM)
• 0.50 lb       Victory Malt (biscuit) (Briess) (28.0 SRM)

Mashed in at 149°F for one hour and mashed out at 168°F for 10 minutes.

Collected close to 6.5 gallons and boiled for 60 minutes:

• 1 oz of Simcoe (12.2% AA) at 60 mintues
• 0.5 oz of Centennial (10% AA) at 60 minutes
• 1 oz of Simcoe (12.2% AA) at 10 mintues
• 1 oz of Centennial (10% AA) at 7 minutes
• 1 oz of Simcoe (12.2% AA) at 5 mintues
• 1 oz of Centennial (10% AA) at 2 minutes

• 0.5 tsp of yeast nutrient at 15 minutes
• 1 whirfloc tablet at 15 minutes

Dry hopping (last two days of fermentation):

• 1 oz Amarillo
• 1 oz Simcoe
• 1 oz Centennial

Cooled by whirlpooling and using a wort chiller 212°F to 70°F in 25 minutes.

Pitched a 3 liter starter of a blend of Rogue PACMAN (Wyeast) and American ale (Wyeast 1056)

Oxygenated for thirty seconds.

• OG: 1.065
• FG: 1.012
• IBUs: ~80 (Tinseth)
• ABV: ~ 7%